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diff --git a/Documentation/power/tuxonice-internals.txt b/Documentation/power/tuxonice-internals.txt deleted file mode 100644 index 0c6a2163a..000000000 --- a/Documentation/power/tuxonice-internals.txt +++ /dev/null @@ -1,532 +0,0 @@ - TuxOnIce 4.0 Internal Documentation. - Updated to 23 March 2015 - -(Please note that incremental image support mentioned in this document is work -in progress. This document may need updating prior to the actual release of -4.0!) - -1. Introduction. - - TuxOnIce 4.0 is an addition to the Linux Kernel, designed to - allow the user to quickly shutdown and quickly boot a computer, without - needing to close documents or programs. It is equivalent to the - hibernate facility in some laptops. This implementation, however, - requires no special BIOS or hardware support. - - The code in these files is based upon the original implementation - prepared by Gabor Kuti and additional work by Pavel Machek and a - host of others. This code has been substantially reworked by Nigel - Cunningham, again with the help and testing of many others, not the - least of whom are Bernard Blackham and Michael Frank. At its heart, - however, the operation is essentially the same as Gabor's version. - -2. Overview of operation. - - The basic sequence of operations is as follows: - - a. Quiesce all other activity. - b. Ensure enough memory and storage space are available, and attempt - to free memory/storage if necessary. - c. Allocate the required memory and storage space. - d. Write the image. - e. Power down. - - There are a number of complicating factors which mean that things are - not as simple as the above would imply, however... - - o The activity of each process must be stopped at a point where it will - not be holding locks necessary for saving the image, or unexpectedly - restart operations due to something like a timeout and thereby make - our image inconsistent. - - o It is desirous that we sync outstanding I/O to disk before calculating - image statistics. This reduces corruption if one should suspend but - then not resume, and also makes later parts of the operation safer (see - below). - - o We need to get as close as we can to an atomic copy of the data. - Inconsistencies in the image will result in inconsistent memory contents at - resume time, and thus in instability of the system and/or file system - corruption. This would appear to imply a maximum image size of one half of - the amount of RAM, but we have a solution... (again, below). - - o In 2.6 and later, we choose to play nicely with the other suspend-to-disk - implementations. - -3. Detailed description of internals. - - a. Quiescing activity. - - Safely quiescing the system is achieved using three separate but related - aspects. - - First, we use the vanilla kerne's support for freezing processes. This code - is based on the observation that the vast majority of processes don't need - to run during suspend. They can be 'frozen'. The kernel therefore - implements a refrigerator routine, which processes enter and in which they - remain until the cycle is complete. Processes enter the refrigerator via - try_to_freeze() invocations at appropriate places. A process cannot be - frozen in any old place. It must not be holding locks that will be needed - for writing the image or freezing other processes. For this reason, - userspace processes generally enter the refrigerator via the signal - handling code, and kernel threads at the place in their event loops where - they drop locks and yield to other processes or sleep. The task of freezing - processes is complicated by the fact that there can be interdependencies - between processes. Freezing process A before process B may mean that - process B cannot be frozen, because it stops at waiting for process A - rather than in the refrigerator. This issue is seen where userspace waits - on freezeable kernel threads or fuse filesystem threads. To address this - issue, we implement the following algorithm for quiescing activity: - - - Freeze filesystems (including fuse - userspace programs starting - new requests are immediately frozen; programs already running - requests complete their work before being frozen in the next - step) - - Freeze userspace - - Thaw filesystems (this is safe now that userspace is frozen and no - fuse requests are outstanding). - - Invoke sys_sync (noop on fuse). - - Freeze filesystems - - Freeze kernel threads - - If we need to free memory, we thaw kernel threads and filesystems, but not - userspace. We can then free caches without worrying about deadlocks due to - swap files being on frozen filesystems or such like. - - b. Ensure enough memory & storage are available. - - We have a number of constraints to meet in order to be able to successfully - suspend and resume. - - First, the image will be written in two parts, described below. One of - these parts needs to have an atomic copy made, which of course implies a - maximum size of one half of the amount of system memory. The other part - ('pageset') is not atomically copied, and can therefore be as large or - small as desired. - - Second, we have constraints on the amount of storage available. In these - calculations, we may also consider any compression that will be done. The - cryptoapi module allows the user to configure an expected compression ratio. - - Third, the user can specify an arbitrary limit on the image size, in - megabytes. This limit is treated as a soft limit, so that we don't fail the - attempt to suspend if we cannot meet this constraint. - - c. Allocate the required memory and storage space. - - Having done the initial freeze, we determine whether the above constraints - are met, and seek to allocate the metadata for the image. If the constraints - are not met, or we fail to allocate the required space for the metadata, we - seek to free the amount of memory that we calculate is needed and try again. - We allow up to four iterations of this loop before aborting the cycle. If - we do fail, it should only be because of a bug in TuxOnIce's calculations - or the vanilla kernel code for freeing memory. - - These steps are merged together in the prepare_image function, found in - prepare_image.c. The functions are merged because of the cyclical nature - of the problem of calculating how much memory and storage is needed. Since - the data structures containing the information about the image must - themselves take memory and use storage, the amount of memory and storage - required changes as we prepare the image. Since the changes are not large, - only one or two iterations will be required to achieve a solution. - - The recursive nature of the algorithm is miminised by keeping user space - frozen while preparing the image, and by the fact that our records of which - pages are to be saved and which pageset they are saved in use bitmaps (so - that changes in number or fragmentation of the pages to be saved don't - feedback via changes in the amount of memory needed for metadata). The - recursiveness is thus limited to any extra slab pages allocated to store the - extents that record storage used, and the effects of seeking to free memory. - - d. Write the image. - - We previously mentioned the need to create an atomic copy of the data, and - the half-of-memory limitation that is implied in this. This limitation is - circumvented by dividing the memory to be saved into two parts, called - pagesets. - - Pageset2 contains most of the page cache - the pages on the active and - inactive LRU lists that aren't needed or modified while TuxOnIce is - running, so they can be safely written without an atomic copy. They are - therefore saved first and reloaded last. While saving these pages, - TuxOnIce carefully ensures that the work of writing the pages doesn't make - the image inconsistent. With the support for Kernel (Video) Mode Setting - going into the kernel at the time of writing, we need to check for pages - on the LRU that are used by KMS, and exclude them from pageset2. They are - atomically copied as part of pageset 1. - - Once pageset2 has been saved, we prepare to do the atomic copy of remaining - memory. As part of the preparation, we power down drivers, thereby providing - them with the opportunity to have their state recorded in the image. The - amount of memory allocated by drivers for this is usually negligible, but if - DRI is in use, video drivers may require significants amounts. Ideally we - would be able to query drivers while preparing the image as to the amount of - memory they will need. Unfortunately no such mechanism exists at the time of - writing. For this reason, TuxOnIce allows the user to set an - 'extra_pages_allowance', which is used to seek to ensure sufficient memory - is available for drivers at this point. TuxOnIce also lets the user set this - value to 0. In this case, a test driver suspend is done while preparing the - image, and the difference (plus a margin) used instead. TuxOnIce will also - automatically restart the hibernation process (twice at most) if it finds - that the extra pages allowance is not sufficient. It will then use what was - actually needed (plus a margin, again). Failure to hibernate should thus - be an extremely rare occurence. - - Having suspended the drivers, we save the CPU context before making an - atomic copy of pageset1, resuming the drivers and saving the atomic copy. - After saving the two pagesets, we just need to save our metadata before - powering down. - - As we mentioned earlier, the contents of pageset2 pages aren't needed once - they've been saved. We therefore use them as the destination of our atomic - copy. In the unlikely event that pageset1 is larger, extra pages are - allocated while the image is being prepared. This is normally only a real - possibility when the system has just been booted and the page cache is - small. - - This is where we need to be careful about syncing, however. Pageset2 will - probably contain filesystem meta data. If this is overwritten with pageset1 - and then a sync occurs, the filesystem will be corrupted - at least until - resume time and another sync of the restored data. Since there is a - possibility that the user might not resume or (may it never be!) that - TuxOnIce might oops, we do our utmost to avoid syncing filesystems after - copying pageset1. - - e. Incremental images - - TuxOnIce 4.0 introduces a new incremental image mode which changes things a - little. When incremental images are enabled, we save a 'normal' image the - first time we hibernate. One resume however, we do not free the image or - the associated storage. Instead, it is retained until the next attempt at - hibernating and a mechanism is enabled which is used to track which pages - of memory are modified between the two cycles. The modified pages can then - be added to the existing image, rather than unmodified pages being saved - again unnecessarily. - - Incremental image support is available in 64 bit Linux only, due to the - requirement for extra page flags. - - This support is accomplished in the following way: - - 1) Tracking of pages. - - The tracking of changed pages is accomplished using the page fault - mechanism. When we reach a point at which we want to start tracking - changes, most pages are marked read-only and also flagged as being - read-only because of this support. Since this cannot happen for every page - of RAM, some are marked as untracked and always treated as modified whn - preparing an incremental iamge. When a process attempts to modify a page - that is marked read-only in this way, a page fault occurs, with TuxOnIce - code marking the page writable and dirty before allowing the write to - continue. In this way, the effect of incremental images on performance is - minimised - a page only causes a fault once. Small modifications to the - page allocator further reduce the number of faults that occur - free pages - are not tracked; they are made writable and marked as dirty as part of - being allocated. - - 2) Saving the incremental image / atomicity. - - The page fault mechanism is also used to improve the means by which - atomicity of the image is acheived. When it is time to do an atomic copy, - the flags for pages are reset, with the result being that it is no longer - necessary for us to do an atomic of pageset1. Instead, we normally write - the uncopied pages to disk. When an attempt is made to modify a page that - has not yet been saved, the page-fault mechanism makes a copy of the page - prior to allowing the write. This copy is then written to disk. Likewise, - on resume, if a process attempts to write to a page that has been read - while the rest of the image is still being loaded, a copy of that page is - made prior to the write being allowed. At the end of loading the image, - modified pages can thus be restored to their 'atomic copy' contents prior - to restarting normal operation. We also mark pages that are yet to be read - as invalid PFNs, so that we can capture as a bug any attempt by a - half-restored kernel to access a page that hasn't yet been reloaded. - - f. Power down. - - Powering down uses standard kernel routines. TuxOnIce supports powering down - using the ACPI S3, S4 and S5 methods or the kernel's non-ACPI power-off. - Supporting suspend to ram (S3) as a power off option might sound strange, - but it allows the user to quickly get their system up and running again if - the battery doesn't run out (we just need to re-read the overwritten pages) - and if the battery does run out (or the user removes power), they can still - resume. - -4. Data Structures. - - TuxOnIce uses three main structures to store its metadata and configuration - information: - - a) Pageflags bitmaps. - - TuxOnIce records which pages will be in pageset1, pageset2, the destination - of the atomic copy and the source of the atomically restored image using - bitmaps. The code used is that written for swsusp, with small improvements - to match TuxOnIce's requirements. - - The pageset1 bitmap is thus easily stored in the image header for use at - resume time. - - As mentioned above, using bitmaps also means that the amount of memory and - storage required for recording the above information is constant. This - greatly simplifies the work of preparing the image. In earlier versions of - TuxOnIce, extents were used to record which pages would be stored. In that - case, however, eating memory could result in greater fragmentation of the - lists of pages, which in turn required more memory to store the extents and - more storage in the image header. These could in turn require further - freeing of memory, and another iteration. All of this complexity is removed - by having bitmaps. - - Bitmaps also make a lot of sense because TuxOnIce only ever iterates - through the lists. There is therefore no cost to not being able to find the - nth page in order 0 time. We only need to worry about the cost of finding - the n+1th page, given the location of the nth page. Bitwise optimisations - help here. - - b) Extents for block data. - - TuxOnIce supports writing the image to multiple block devices. In the case - of swap, multiple partitions and/or files may be in use, and we happily use - them all (with the exception of compcache pages, which we allocate but do - not use). This use of multiple block devices is accomplished as follows: - - Whatever the actual source of the allocated storage, the destination of the - image can be viewed in terms of one or more block devices, and on each - device, a list of sectors. To simplify matters, we only use contiguous, - PAGE_SIZE aligned sectors, like the swap code does. - - Since sector numbers on each bdev may well not start at 0, it makes much - more sense to use extents here. Contiguous ranges of pages can thus be - represented in the extents by contiguous values. - - Variations in block size are taken account of in transforming this data - into the parameters for bio submission. - - We can thus implement a layer of abstraction wherein the core of TuxOnIce - doesn't have to worry about which device we're currently writing to or - where in the device we are. It simply requests that the next page in the - pageset or header be written, leaving the details to this lower layer. - The lower layer remembers where in the sequence of devices and blocks each - pageset starts. The header always starts at the beginning of the allocated - storage. - - So extents are: - - struct extent { - unsigned long minimum, maximum; - struct extent *next; - } - - These are combined into chains of extents for a device: - - struct extent_chain { - int size; /* size of the extent ie sum (max-min+1) */ - int allocs, frees; - char *name; - struct extent *first, *last_touched; - }; - - For each bdev, we need to store a little more info (simplified definition): - - struct toi_bdev_info { - struct block_device *bdev; - - char uuid[17]; - dev_t dev_t; - int bmap_shift; - int blocks_per_page; - }; - - The uuid is the main means used to identify the device in the storage - image. This means we can cope with the dev_t representation of a device - changing between saving the image and restoring it, as may happen on some - bioses or in the LVM case. - - bmap_shift and blocks_per_page apply the effects of variations in blocks - per page settings for the filesystem and underlying bdev. For most - filesystems, these are the same, but for xfs, they can have independant - values. - - Combining these two structures together, we have everything we need to - record what devices and what blocks on each device are being used to - store the image, and to submit i/o using bio_submit. - - The last elements in the picture are a means of recording how the storage - is being used. - - We do this first and foremost by implementing a layer of abstraction on - top of the devices and extent chains which allows us to view however many - devices there might be as one long storage tape, with a single 'head' that - tracks a 'current position' on the tape: - - struct extent_iterate_state { - struct extent_chain *chains; - int num_chains; - int current_chain; - struct extent *current_extent; - unsigned long current_offset; - }; - - That is, *chains points to an array of size num_chains of extent chains. - For the filewriter, this is always a single chain. For the swapwriter, the - array is of size MAX_SWAPFILES. - - current_chain, current_extent and current_offset thus point to the current - index in the chains array (and into a matching array of struct - suspend_bdev_info), the current extent in that chain (to optimise access), - and the current value in the offset. - - The image is divided into three parts: - - The header - - Pageset 1 - - Pageset 2 - - The header always starts at the first device and first block. We know its - size before we begin to save the image because we carefully account for - everything that will be stored in it. - - The second pageset (LRU) is stored first. It begins on the next page after - the end of the header. - - The first pageset is stored second. It's start location is only known once - pageset2 has been saved, since pageset2 may be compressed as it is written. - This location is thus recorded at the end of saving pageset2. It is page - aligned also. - - Since this information is needed at resume time, and the location of extents - in memory will differ at resume time, this needs to be stored in a portable - way: - - struct extent_iterate_saved_state { - int chain_num; - int extent_num; - unsigned long offset; - }; - - We can thus implement a layer of abstraction wherein the core of TuxOnIce - doesn't have to worry about which device we're currently writing to or - where in the device we are. It simply requests that the next page in the - pageset or header be written, leaving the details to this layer, and - invokes the routines to remember and restore the position, without having - to worry about the details of how the data is arranged on disk or such like. - - c) Modules - - One aim in designing TuxOnIce was to make it flexible. We wanted to allow - for the implementation of different methods of transforming a page to be - written to disk and different methods of getting the pages stored. - - In early versions (the betas and perhaps Suspend1), compression support was - inlined in the image writing code, and the data structures and code for - managing swap were intertwined with the rest of the code. A number of people - had expressed interest in implementing image encryption, and alternative - methods of storing the image. - - In order to achieve this, TuxOnIce was given a modular design. - - A module is a single file which encapsulates the functionality needed - to transform a pageset of data (encryption or compression, for example), - or to write the pageset to a device. The former type of module is called - a 'page-transformer', the later a 'writer'. - - Modules are linked together in pipeline fashion. There may be zero or more - page transformers in a pipeline, and there is always exactly one writer. - The pipeline follows this pattern: - - --------------------------------- - | TuxOnIce Core | - --------------------------------- - | - | - --------------------------------- - | Page transformer 1 | - --------------------------------- - | - | - --------------------------------- - | Page transformer 2 | - --------------------------------- - | - | - --------------------------------- - | Writer | - --------------------------------- - - During the writing of an image, the core code feeds pages one at a time - to the first module. This module performs whatever transformations it - implements on the incoming data, completely consuming the incoming data and - feeding output in a similar manner to the next module. - - All routines are SMP safe, and the final result of the transformations is - written with an index (provided by the core) and size of the output by the - writer. As a result, we can have multithreaded I/O without needing to - worry about the sequence in which pages are written (or read). - - During reading, the pipeline works in the reverse direction. The core code - calls the first module with the address of a buffer which should be filled. - (Note that the buffer size is always PAGE_SIZE at this time). This module - will in turn request data from the next module and so on down until the - writer is made to read from the stored image. - - Part of definition of the structure of a module thus looks like this: - - int (*rw_init) (int rw, int stream_number); - int (*rw_cleanup) (int rw); - int (*write_chunk) (struct page *buffer_page); - int (*read_chunk) (struct page *buffer_page, int sync); - - It should be noted that the _cleanup routine may be called before the - full stream of data has been read or written. While writing the image, - the user may (depending upon settings) choose to abort suspending, and - if we are in the midst of writing the last portion of the image, a portion - of the second pageset may be reread. This may also happen if an error - occurs and we seek to abort the process of writing the image. - - The modular design is also useful in a number of other ways. It provides - a means where by we can add support for: - - - providing overall initialisation and cleanup routines; - - serialising configuration information in the image header; - - providing debugging information to the user; - - determining memory and image storage requirements; - - dis/enabling components at run-time; - - configuring the module (see below); - - ...and routines for writers specific to their work: - - Parsing a resume= location; - - Determining whether an image exists; - - Marking a resume as having been attempted; - - Invalidating an image; - - Since some parts of the core - the user interface and storage manager - support - have use for some of these functions, they are registered as - 'miscellaneous' modules as well. - - d) Sysfs data structures. - - This brings us naturally to support for configuring TuxOnIce. We desired to - provide a way to make TuxOnIce as flexible and configurable as possible. - The user shouldn't have to reboot just because they want to now hibernate to - a file instead of a partition, for example. - - To accomplish this, TuxOnIce implements a very generic means whereby the - core and modules can register new sysfs entries. All TuxOnIce entries use - a single _store and _show routine, both of which are found in - tuxonice_sysfs.c in the kernel/power directory. These routines handle the - most common operations - getting and setting the values of bits, integers, - longs, unsigned longs and strings in one place, and allow overrides for - customised get and set options as well as side-effect routines for all - reads and writes. - - When combined with some simple macros, a new sysfs entry can then be defined - in just a couple of lines: - - SYSFS_INT("progress_granularity", SYSFS_RW, &progress_granularity, 1, - 2048, 0, NULL), - - This defines a sysfs entry named "progress_granularity" which is rw and - allows the user to access an integer stored at &progress_granularity, giving - it a value between 1 and 2048 inclusive. - - Sysfs entries are registered under /sys/power/tuxonice, and entries for - modules are located in a subdirectory named after the module. - diff --git a/Documentation/power/tuxonice.txt b/Documentation/power/tuxonice.txt deleted file mode 100644 index 3bf0575ef..000000000 --- a/Documentation/power/tuxonice.txt +++ /dev/null @@ -1,948 +0,0 @@ - --- TuxOnIce, version 3.0 --- - -1. What is it? -2. Why would you want it? -3. What do you need to use it? -4. Why not just use the version already in the kernel? -5. How do you use it? -6. What do all those entries in /sys/power/tuxonice do? -7. How do you get support? -8. I think I've found a bug. What should I do? -9. When will XXX be supported? -10 How does it work? -11. Who wrote TuxOnIce? - -1. What is it? - - Imagine you're sitting at your computer, working away. For some reason, you - need to turn off your computer for a while - perhaps it's time to go home - for the day. When you come back to your computer next, you're going to want - to carry on where you left off. Now imagine that you could push a button and - have your computer store the contents of its memory to disk and power down. - Then, when you next start up your computer, it loads that image back into - memory and you can carry on from where you were, just as if you'd never - turned the computer off. You have far less time to start up, no reopening of - applications or finding what directory you put that file in yesterday. - That's what TuxOnIce does. - - TuxOnIce has a long heritage. It began life as work by Gabor Kuti, who, - with some help from Pavel Machek, got an early version going in 1999. The - project was then taken over by Florent Chabaud while still in alpha version - numbers. Nigel Cunningham came on the scene when Florent was unable to - continue, moving the project into betas, then 1.0, 2.0 and so on up to - the present series. During the 2.0 series, the name was contracted to - Suspend2 and the website suspend2.net created. Beginning around July 2007, - a transition to calling the software TuxOnIce was made, to seek to help - make it clear that TuxOnIce is more concerned with hibernation than suspend - to ram. - - Pavel Machek's swsusp code, which was merged around 2.5.17 retains the - original name, and was essentially a fork of the beta code until Rafael - Wysocki came on the scene in 2005 and began to improve it further. - -2. Why would you want it? - - Why wouldn't you want it? - - Being able to save the state of your system and quickly restore it improves - your productivity - you get a useful system in far less time than through - the normal boot process. You also get to be completely 'green', using zero - power, or as close to that as possible (the computer may still provide - minimal power to some devices, so they can initiate a power on, but that - will be the same amount of power as would be used if you told the computer - to shutdown. - -3. What do you need to use it? - - a. Kernel Support. - - i) The TuxOnIce patch. - - TuxOnIce is part of the Linux Kernel. This version is not part of Linus's - 2.6 tree at the moment, so you will need to download the kernel source and - apply the latest patch. Having done that, enable the appropriate options in - make [menu|x]config (under Power Management Options - look for "Enhanced - Hibernation"), compile and install your kernel. TuxOnIce works with SMP, - Highmem, preemption, fuse filesystems, x86-32, PPC and x86_64. - - TuxOnIce patches are available from http://tuxonice.net. - - ii) Compression support. - - Compression support is implemented via the cryptoapi. You will therefore want - to select any Cryptoapi transforms that you want to use on your image from - the Cryptoapi menu while configuring your kernel. We recommend the use of the - LZO compression method - it is very fast and still achieves good compression. - - You can also tell TuxOnIce to write its image to an encrypted and/or - compressed filesystem/swap partition. In that case, you don't need to do - anything special for TuxOnIce when it comes to kernel configuration. - - iii) Configuring other options. - - While you're configuring your kernel, try to configure as much as possible - to build as modules. We recommend this because there are a number of drivers - that are still in the process of implementing proper power management - support. In those cases, the best way to work around their current lack is - to build them as modules and remove the modules while hibernating. You might - also bug the driver authors to get their support up to speed, or even help! - - b. Storage. - - i) Swap. - - TuxOnIce can store the hibernation image in your swap partition, a swap file or - a combination thereof. Whichever combination you choose, you will probably - want to create enough swap space to store the largest image you could have, - plus the space you'd normally use for swap. A good rule of thumb would be - to calculate the amount of swap you'd want without using TuxOnIce, and then - add the amount of memory you have. This swapspace can be arranged in any way - you'd like. It can be in one partition or file, or spread over a number. The - only requirement is that they be active when you start a hibernation cycle. - - There is one exception to this requirement. TuxOnIce has the ability to turn - on one swap file or partition at the start of hibernating and turn it back off - at the end. If you want to ensure you have enough memory to store a image - when your memory is fully used, you might want to make one swap partition or - file for 'normal' use, and another for TuxOnIce to activate & deactivate - automatically. (Further details below). - - ii) Normal files. - - TuxOnIce includes a 'file allocator'. The file allocator can store your - image in a simple file. Since Linux has the concept of everything being a - file, this is more powerful than it initially sounds. If, for example, you - were to set up a network block device file, you could hibernate to a network - server. This has been tested and works to a point, but nbd itself isn't - stateless enough for our purposes. - - Take extra care when setting up the file allocator. If you just type - commands without thinking and then try to hibernate, you could cause - irreversible corruption on your filesystems! Make sure you have backups. - - Most people will only want to hibernate to a local file. To achieve that, do - something along the lines of: - - echo "TuxOnIce" > /hibernation-file - dd if=/dev/zero bs=1M count=512 >> /hibernation-file - - This will create a 512MB file called /hibernation-file. To get TuxOnIce to use - it: - - echo /hibernation-file > /sys/power/tuxonice/file/target - - Then - - cat /sys/power/tuxonice/resume - - Put the results of this into your bootloader's configuration (see also step - C, below): - - ---EXAMPLE-ONLY-DON'T-COPY-AND-PASTE--- - # cat /sys/power/tuxonice/resume - file:/dev/hda2:0x1e001 - - In this example, we would edit the append= line of our lilo.conf|menu.lst - so that it included: - - resume=file:/dev/hda2:0x1e001 - ---EXAMPLE-ONLY-DON'T-COPY-AND-PASTE--- - - For those who are thinking 'Could I make the file sparse?', the answer is - 'No!'. At the moment, there is no way for TuxOnIce to fill in the holes in - a sparse file while hibernating. In the longer term (post merge!), I'd like - to change things so that the file could be dynamically resized and have - holes filled as needed. Right now, however, that's not possible and not a - priority. - - c. Bootloader configuration. - - Using TuxOnIce also requires that you add an extra parameter to - your lilo.conf or equivalent. Here's an example for a swap partition: - - append="resume=swap:/dev/hda1" - - This would tell TuxOnIce that /dev/hda1 is a swap partition you - have. TuxOnIce will use the swap signature of this partition as a - pointer to your data when you hibernate. This means that (in this example) - /dev/hda1 doesn't need to be _the_ swap partition where all of your data - is actually stored. It just needs to be a swap partition that has a - valid signature. - - You don't need to have a swap partition for this purpose. TuxOnIce - can also use a swap file, but usage is a little more complex. Having made - your swap file, turn it on and do - - cat /sys/power/tuxonice/swap/headerlocations - - (this assumes you've already compiled your kernel with TuxOnIce - support and booted it). The results of the cat command will tell you - what you need to put in lilo.conf: - - For swap partitions like /dev/hda1, simply use resume=/dev/hda1. - For swapfile `swapfile`, use resume=swap:/dev/hda2:0x242d. - - If the swapfile changes for any reason (it is moved to a different - location, it is deleted and recreated, or the filesystem is - defragmented) then you will have to check - /sys/power/tuxonice/swap/headerlocations for a new resume_block value. - - Once you've compiled and installed the kernel and adjusted your bootloader - configuration, you should only need to reboot for the most basic part - of TuxOnIce to be ready. - - If you only compile in the swap allocator, or only compile in the file - allocator, you don't need to add the "swap:" part of the resume= - parameters above. resume=/dev/hda2:0x242d will work just as well. If you - have compiled both and your storage is on swap, you can also use this - format (the swap allocator is the default allocator). - - When compiling your kernel, one of the options in the 'Power Management - Support' menu, just above the 'Enhanced Hibernation (TuxOnIce)' entry is - called 'Default resume partition'. This can be used to set a default value - for the resume= parameter. - - d. The hibernate script. - - Since the driver model in 2.6 kernels is still being developed, you may need - to do more than just configure TuxOnIce. Users of TuxOnIce usually start the - process via a script which prepares for the hibernation cycle, tells the - kernel to do its stuff and then restore things afterwards. This script might - involve: - - - Switching to a text console and back if X doesn't like the video card - status on resume. - - Un/reloading drivers that don't play well with hibernation. - - Note that you might not be able to unload some drivers if there are - processes using them. You might have to kill off processes that hold - devices open. Hint: if your X server accesses an USB mouse, doing a - 'chvt' to a text console releases the device and you can unload the - module. - - Check out the latest script (available on tuxonice.net). - - e. The userspace user interface. - - TuxOnIce has very limited support for displaying status if you only apply - the kernel patch - it can printk messages, but that is all. In addition, - some of the functions mentioned in this document (such as cancelling a cycle - or performing interactive debugging) are unavailable. To utilise these - functions, or simply get a nice display, you need the 'userui' component. - Userui comes in three flavours, usplash, fbsplash and text. Text should - work on any console. Usplash and fbsplash require the appropriate - (distro specific?) support. - - To utilise a userui, TuxOnIce just needs to be told where to find the - userspace binary: - - echo "/usr/local/sbin/tuxoniceui_fbsplash" > /sys/power/tuxonice/user_interface/program - - The hibernate script can do this for you, and a default value for this - setting can be configured when compiling the kernel. This path is also - stored in the image header, so if you have an initrd or initramfs, you can - use the userui during the first part of resuming (prior to the atomic - restore) by putting the binary in the same path in your initrd/ramfs. - Alternatively, you can put it in a different location and do an echo - similar to the above prior to the echo > do_resume. The value saved in the - image header will then be ignored. - -4. Why not just use the version already in the kernel? - - The version in the vanilla kernel has a number of drawbacks. The most - serious of these are: - - it has a maximum image size of 1/2 total memory; - - it doesn't allocate storage until after it has snapshotted memory. - This means that you can't be sure hibernating will work until you - see it start to write the image; - - it does not allow you to press escape to cancel a cycle; - - it does not allow you to press escape to cancel resuming; - - it does not allow you to automatically swapon a file when - starting a cycle; - - it does not allow you to use multiple swap partitions or files; - - it does not allow you to use ordinary files; - - it just invalidates an image and continues to boot if you - accidentally boot the wrong kernel after hibernating; - - it doesn't support any sort of nice display while hibernating; - - it is moving toward requiring that you have an initrd/initramfs - to ever have a hope of resuming (uswsusp). While uswsusp will - address some of the concerns above, it won't address all of them, - and will be more complicated to get set up; - - it doesn't have support for suspend-to-both (write a hibernation - image, then suspend to ram; I think this is known as ReadySafe - under M$). - -5. How do you use it? - - A hibernation cycle can be started directly by doing: - - echo > /sys/power/tuxonice/do_hibernate - - In practice, though, you'll probably want to use the hibernate script - to unload modules, configure the kernel the way you like it and so on. - In that case, you'd do (as root): - - hibernate - - See the hibernate script's man page for more details on the options it - takes. - - If you're using the text or splash user interface modules, one feature of - TuxOnIce that you might find useful is that you can press Escape at any time - during hibernating, and the process will be aborted. - - Due to the way hibernation works, this means you'll have your system back and - perfectly usable almost instantly. The only exception is when it's at the - very end of writing the image. Then it will need to reload a small (usually - 4-50MBs, depending upon the image characteristics) portion first. - - Likewise, when resuming, you can press escape and resuming will be aborted. - The computer will then powerdown again according to settings at that time for - the powerdown method or rebooting. - - You can change the settings for powering down while the image is being - written by pressing 'R' to toggle rebooting and 'O' to toggle between - suspending to ram and powering down completely). - - If you run into problems with resuming, adding the "noresume" option to - the kernel command line will let you skip the resume step and recover your - system. This option shouldn't normally be needed, because TuxOnIce modifies - the image header prior to the atomic restore, and will thus prompt you - if it detects that you've tried to resume an image before (this flag is - removed if you press Escape to cancel a resume, so you won't be prompted - then). - - Recent kernels (2.6.24 onwards) add support for resuming from a different - kernel to the one that was hibernated (thanks to Rafael for his work on - this - I've just embraced and enhanced the support for TuxOnIce). This - should further reduce the need for you to use the noresume option. - -6. What do all those entries in /sys/power/tuxonice do? - - /sys/power/tuxonice is the directory which contains files you can use to - tune and configure TuxOnIce to your liking. The exact contents of - the directory will depend upon the version of TuxOnIce you're - running and the options you selected at compile time. In the following - descriptions, names in brackets refer to compile time options. - (Note that they're all dependant upon you having selected CONFIG_TUXONICE - in the first place!). - - Since the values of these settings can open potential security risks, the - writeable ones are accessible only to the root user. You may want to - configure sudo to allow you to invoke your hibernate script as an ordinary - user. - - - alloc/failure_test - - This debugging option provides a way of testing TuxOnIce's handling of - memory allocation failures. Each allocation type that TuxOnIce makes has - been given a unique number (see the source code). Echo the appropriate - number into this entry, and when TuxOnIce attempts to do that allocation, - it will pretend there was a failure and act accordingly. - - - alloc/find_max_mem_allocated - - This debugging option will cause TuxOnIce to find the maximum amount of - memory it used during a cycle, and report that information in debugging - information at the end of the cycle. - - - alt_resume_param - - Instead of powering down after writing a hibernation image, TuxOnIce - supports resuming from a different image. This entry lets you set the - location of the signature for that image (the resume= value you'd use - for it). Using an alternate image and keep_image mode, you can do things - like using an alternate image to power down an uninterruptible power - supply. - - - block_io/target_outstanding_io - - This value controls the amount of memory that the block I/O code says it - needs when the core code is calculating how much memory is needed for - hibernating and for resuming. It doesn't directly control the amount of - I/O that is submitted at any one time - that depends on the amount of - available memory (we may have more available than we asked for), the - throughput that is being achieved and the ability of the CPU to keep up - with disk throughput (particularly where we're compressing pages). - - - checksum/enabled - - Use cryptoapi hashing routines to verify that Pageset2 pages don't change - while we're saving the first part of the image, and to get any pages that - do change resaved in the atomic copy. This should normally not be needed, - but if you're seeing issues, please enable this. If your issues stop you - being able to resume, enable this option, hibernate and cancel the cycle - after the atomic copy is done. If the debugging info shows a non-zero - number of pages resaved, please report this to Nigel. - - - compression/algorithm - - Set the cryptoapi algorithm used for compressing the image. - - - compression/expected_compression - - These values allow you to set an expected compression ratio, which TuxOnice - will use in calculating whether it meets constraints on the image size. If - this expected compression ratio is not attained, the hibernation cycle will - abort, so it is wise to allow some spare. You can see what compression - ratio is achieved in the logs after hibernating. - - - debug_info: - - This file returns information about your configuration that may be helpful - in diagnosing problems with hibernating. - - - did_suspend_to_both: - - This file can be used when you hibernate with powerdown method 3 (ie suspend - to ram after writing the image). There can be two outcomes in this case. We - can resume from the suspend-to-ram before the battery runs out, or we can run - out of juice and and up resuming like normal. This entry lets you find out, - post resume, which way we went. If the value is 1, we resumed from suspend - to ram. This can be useful when actions need to be run post suspend-to-ram - that don't need to be run if we did the normal resume from power off. - - - do_hibernate: - - When anything is written to this file, the kernel side of TuxOnIce will - begin to attempt to write an image to disk and power down. You'll normally - want to run the hibernate script instead, to get modules unloaded first. - - - do_resume: - - When anything is written to this file TuxOnIce will attempt to read and - restore an image. If there is no image, it will return almost immediately. - If an image exists, the echo > will never return. Instead, the original - kernel context will be restored and the original echo > do_hibernate will - return. - - - */enabled - - These option can be used to temporarily disable various parts of TuxOnIce. - - - extra_pages_allowance - - When TuxOnIce does its atomic copy, it calls the driver model suspend - and resume methods. If you have DRI enabled with a driver such as fglrx, - this can result in the driver allocating a substantial amount of memory - for storing its state. Extra_pages_allowance tells TuxOnIce how much - extra memory it should ensure is available for those allocations. If - your attempts at hibernating end with a message in dmesg indicating that - insufficient extra pages were allowed, you need to increase this value. - - - file/target: - - Read this value to get the current setting. Write to it to point TuxOnice - at a new storage location for the file allocator. See section 3.b.ii above - for details of how to set up the file allocator. - - - freezer_test - - This entry can be used to get TuxOnIce to just test the freezer and prepare - an image without actually doing a hibernation cycle. It is useful for - diagnosing freezing and image preparation issues. - - - full_pageset2 - - TuxOnIce divides the pages that are stored in an image into two sets. The - difference between the two sets is that pages in pageset 1 are atomically - copied, and pages in pageset 2 are written to disk without being copied - first. A page CAN be written to disk without being copied first if and only - if its contents will not be modified or used at any time after userspace - processes are frozen. A page MUST be in pageset 1 if its contents are - modified or used at any time after userspace processes have been frozen. - - Normally (ie if this option is enabled), TuxOnIce will put all pages on the - per-zone LRUs in pageset2, then remove those pages used by any userspace - user interface helper and TuxOnIce storage manager that are running, - together with pages used by the GEM memory manager introduced around 2.6.28 - kernels. - - If this option is disabled, a much more conservative approach will be taken. - The only pages in pageset2 will be those belonging to userspace processes, - with the exclusion of those belonging to the TuxOnIce userspace helpers - mentioned above. This will result in a much smaller pageset2, and will - therefore result in smaller images than are possible with this option - enabled. - - - ignore_rootfs - - TuxOnIce records which device is mounted as the root filesystem when - writing the hibernation image. It will normally check at resume time that - this device isn't already mounted - that would be a cause of filesystem - corruption. In some particular cases (RAM based root filesystems), you - might want to disable this check. This option allows you to do that. - - - image_exists: - - Can be used in a script to determine whether a valid image exists at the - location currently pointed to by resume=. Returns up to three lines. - The first is whether an image exists (-1 for unsure, otherwise 0 or 1). - If an image eixsts, additional lines will return the machine and version. - Echoing anything to this entry removes any current image. - - - image_size_limit: - - The maximum size of hibernation image written to disk, measured in megabytes - (1024*1024). - - - last_result: - - The result of the last hibernation cycle, as defined in - include/linux/suspend-debug.h with the values SUSPEND_ABORTED to - SUSPEND_KEPT_IMAGE. This is a bitmask. - - - late_cpu_hotplug: - - This sysfs entry controls whether cpu hotplugging is done - as normal - just - before (unplug) and after (replug) the atomic copy/restore (so that all - CPUs/cores are available for multithreaded I/O). The alternative is to - unplug all secondary CPUs/cores at the start of hibernating/resuming, and - replug them at the end of resuming. No multithreaded I/O will be possible in - this configuration, but the odd machine has been reported to require it. - - - lid_file: - - This determines which ACPI button file we look in to determine whether the - lid is open or closed after resuming from suspend to disk or power off. - If the entry is set to "lid/LID", we'll open /proc/acpi/button/lid/LID/state - and check its contents at the appropriate moment. See post_wake_state below - for more details on how this entry is used. - - - log_everything (CONFIG_PM_DEBUG): - - Setting this option results in all messages printed being logged. Normally, - only a subset are logged, so as to not slow the process and not clutter the - logs. Useful for debugging. It can be toggled during a cycle by pressing - 'L'. - - - no_load_direct: - - This is a debugging option. If, when loading the atomically copied pages of - an image, TuxOnIce finds that the destination address for a page is free, - it will normally allocate the image, load the data directly into that - address and skip it in the atomic restore. If this option is disabled, the - page will be loaded somewhere else and atomically restored like other pages. - - - no_flusher_thread: - - When doing multithreaded I/O (see below), the first online CPU can be used - to _just_ submit compressed pages when writing the image, rather than - compressing and submitting data. This option is normally disabled, but has - been included because Nigel would like to see whether it will be more useful - as the number of cores/cpus in computers increases. - - - no_multithreaded_io: - - TuxOnIce will normally create one thread per cpu/core on your computer, - each of which will then perform I/O. This will generally result in - throughput that's the maximum the storage medium can handle. There - shouldn't be any reason to disable multithreaded I/O now, but this option - has been retained for debugging purposes. - - - no_pageset2 - - See the entry for full_pageset2 above for an explanation of pagesets. - Enabling this option causes TuxOnIce to do an atomic copy of all pages, - thereby limiting the maximum image size to 1/2 of memory, as swsusp does. - - - no_pageset2_if_unneeded - - See the entry for full_pageset2 above for an explanation of pagesets. - Enabling this option causes TuxOnIce to act like no_pageset2 was enabled - if and only it isn't needed anyway. This option may still make TuxOnIce - less reliable because pageset2 pages are normally used to store the - atomic copy - drivers that want to do allocations of larger amounts of - memory in one shot will be more likely to find that those amounts aren't - available if this option is enabled. - - - pause_between_steps (CONFIG_PM_DEBUG): - - This option is used during debugging, to make TuxOnIce pause between - each step of the process. It is ignored when the nice display is on. - - - post_wake_state: - - TuxOnIce provides support for automatically waking after a user-selected - delay, and using a different powerdown method if the lid is still closed. - (Yes, we're assuming a laptop). This entry lets you choose what state - should be entered next. The values are those described under - powerdown_method, below. It can be used to suspend to RAM after hibernating, - then powerdown properly (say) 20 minutes. It can also be used to power down - properly, then wake at (say) 6.30am and suspend to RAM until you're ready - to use the machine. - - - powerdown_method: - - Used to select a method by which TuxOnIce should powerdown after writing the - image. Currently: - - 0: Don't use ACPI to power off. - 3: Attempt to enter Suspend-to-ram. - 4: Attempt to enter ACPI S4 mode. - 5: Attempt to power down via ACPI S5 mode. - - Note that these options are highly dependant upon your hardware & software: - - 3: When succesful, your machine suspends to ram instead of powering off. - The advantage of using this mode is that it doesn't matter whether your - battery has enough charge to make it through to your next resume. If it - lasts, you will simply resume from suspend to ram (and the image on disk - will be discarded). If the battery runs out, you will resume from disk - instead. The disadvantage is that it takes longer than a normal - suspend-to-ram to enter the state, since the suspend-to-disk image needs - to be written first. - 4/5: When successful, your machine will be off and comsume (almost) no power. - But it might still react to some external events like opening the lid or - trafic on a network or usb device. For the bios, resume is then the same - as warm boot, similar to a situation where you used the command `reboot' - to reboot your machine. If your machine has problems on warm boot or if - you want to protect your machine with the bios password, this is probably - not the right choice. Mode 4 may be necessary on some machines where ACPI - wake up methods need to be run to properly reinitialise hardware after a - hibernation cycle. - 0: Switch the machine completely off. The only possible wakeup is the power - button. For the bios, resume is then the same as a cold boot, in - particular you would have to provide your bios boot password if your - machine uses that feature for booting. - - - progressbar_granularity_limit: - - This option can be used to limit the granularity of the progress bar - displayed with a bootsplash screen. The value is the maximum number of - steps. That is, 10 will make the progress bar jump in 10% increments. - - - reboot: - - This option causes TuxOnIce to reboot rather than powering down - at the end of saving an image. It can be toggled during a cycle by pressing - 'R'. - - - resume: - - This sysfs entry can be used to read and set the location in which TuxOnIce - will look for the signature of an image - the value set using resume= at - boot time or CONFIG_PM_STD_PARTITION ("Default resume partition"). By - writing to this file as well as modifying your bootloader's configuration - file (eg menu.lst), you can set or reset the location of your image or the - method of storing the image without rebooting. - - - replace_swsusp (CONFIG_TOI_REPLACE_SWSUSP): - - This option makes - - echo disk > /sys/power/state - - activate TuxOnIce instead of swsusp. Regardless of whether this option is - enabled, any invocation of swsusp's resume time trigger will cause TuxOnIce - to check for an image too. This is due to the fact that at resume time, we - can't know whether this option was enabled until we see if an image is there - for us to resume from. (And when an image exists, we don't care whether we - did replace swsusp anyway - we just want to resume). - - - resume_commandline: - - This entry can be read after resuming to see the commandline that was used - when resuming began. You might use this to set up two bootloader entries - that are the same apart from the fact that one includes a extra append= - argument "at_work=1". You could then grep resume_commandline in your - post-resume scripts and configure networking (for example) differently - depending upon whether you're at home or work. resume_commandline can be - set to arbitrary text if you wish to remove sensitive contents. - - - swap/swapfilename: - - This entry is used to specify the swapfile or partition that - TuxOnIce will attempt to swapon/swapoff automatically. Thus, if - I normally use /dev/hda1 for swap, and want to use /dev/hda2 for specifically - for my hibernation image, I would - - echo /dev/hda2 > /sys/power/tuxonice/swap/swapfile - - /dev/hda2 would then be automatically swapon'd and swapoff'd. Note that the - swapon and swapoff occur while other processes are frozen (including kswapd) - so this swap file will not be used up when attempting to free memory. The - parition/file is also given the highest priority, so other swapfiles/partitions - will only be used to save the image when this one is filled. - - The value of this file is used by headerlocations along with any currently - activated swapfiles/partitions. - - - swap/headerlocations: - - This option tells you the resume= options to use for swap devices you - currently have activated. It is particularly useful when you only want to - use a swap file to store your image. See above for further details. - - - test_bio - - This is a debugging option. When enabled, TuxOnIce will not hibernate. - Instead, when asked to write an image, it will skip the atomic copy, - just doing the writing of the image and then returning control to the - user at the point where it would have powered off. This is useful for - testing throughput in different configurations. - - - test_filter_speed - - This is a debugging option. When enabled, TuxOnIce will not hibernate. - Instead, when asked to write an image, it will not write anything or do - an atomic copy, but will only run any enabled compression algorithm on the - data that would have been written (the source pages of the atomic copy in - the case of pageset 1). This is useful for comparing the performance of - compression algorithms and for determining the extent to which an upgrade - to your storage method would improve hibernation speed. - - - user_interface/debug_sections (CONFIG_PM_DEBUG): - - This value, together with the console log level, controls what debugging - information is displayed. The console log level determines the level of - detail, and this value determines what detail is displayed. This value is - a bit vector, and the meaning of the bits can be found in the kernel tree - in include/linux/tuxonice.h. It can be overridden using the kernel's - command line option suspend_dbg. - - - user_interface/default_console_level (CONFIG_PM_DEBUG): - - This determines the value of the console log level at the start of a - hibernation cycle. If debugging is compiled in, the console log level can be - changed during a cycle by pressing the digit keys. Meanings are: - - 0: Nice display. - 1: Nice display plus numerical progress. - 2: Errors only. - 3: Low level debugging info. - 4: Medium level debugging info. - 5: High level debugging info. - 6: Verbose debugging info. - - - user_interface/enable_escape: - - Setting this to "1" will enable you abort a hibernation cycle or resuming by - pressing escape, "0" (default) disables this feature. Note that enabling - this option means that you cannot initiate a hibernation cycle and then walk - away from your computer, expecting it to be secure. With feature disabled, - you can validly have this expectation once TuxOnice begins to write the - image to disk. (Prior to this point, it is possible that TuxOnice might - about because of failure to freeze all processes or because constraints - on its ability to save the image are not met). - - - user_interface/program - - This entry is used to tell TuxOnice what userspace program to use for - providing a user interface while hibernating. The program uses a netlink - socket to pass messages back and forward to the kernel, allowing all of the - functions formerly implemented in the kernel user interface components. - - - version: - - The version of TuxOnIce you have compiled into the currently running kernel. - - - wake_alarm_dir: - - As mentioned above (post_wake_state), TuxOnIce supports automatically waking - after some delay. This entry allows you to select which wake alarm to use. - It should contain the value "rtc0" if you're wanting to use - /sys/class/rtc/rtc0. - - - wake_delay: - - This value determines the delay from the end of writing the image until the - wake alarm is triggered. You can set an absolute time by writing the desired - time into /sys/class/rtc/<wake_alarm_dir>/wakealarm and leaving these values - empty. - - Note that for the wakeup to actually occur, you may need to modify entries - in /proc/acpi/wakeup. This is done by echoing the name of the button in the - first column (eg PBTN) into the file. - -7. How do you get support? - - Glad you asked. TuxOnIce is being actively maintained and supported - by Nigel (the guy doing most of the kernel coding at the moment), Bernard - (who maintains the hibernate script and userspace user interface components) - and its users. - - Resources availble include HowTos, FAQs and a Wiki, all available via - tuxonice.net. You can find the mailing lists there. - -8. I think I've found a bug. What should I do? - - By far and a way, the most common problems people have with TuxOnIce - related to drivers not having adequate power management support. In this - case, it is not a bug with TuxOnIce, but we can still help you. As we - mentioned above, such issues can usually be worked around by building the - functionality as modules and unloading them while hibernating. Please visit - the Wiki for up-to-date lists of known issues and work arounds. - - If this information doesn't help, try running: - - hibernate --bug-report - - ..and sending the output to the users mailing list. - - Good information on how to provide us with useful information from an - oops is found in the file REPORTING-BUGS, in the top level directory - of the kernel tree. If you get an oops, please especially note the - information about running what is printed on the screen through ksymoops. - The raw information is useless. - -9. When will XXX be supported? - - If there's a feature missing from TuxOnIce that you'd like, feel free to - ask. We try to be obliging, within reason. - - Patches are welcome. Please send to the list. - -10. How does it work? - - TuxOnIce does its work in a number of steps. - - a. Freezing system activity. - - The first main stage in hibernating is to stop all other activity. This is - achieved in stages. Processes are considered in fours groups, which we will - describe in reverse order for clarity's sake: Threads with the PF_NOFREEZE - flag, kernel threads without this flag, userspace processes with the - PF_SYNCTHREAD flag and all other processes. The first set (PF_NOFREEZE) are - untouched by the refrigerator code. They are allowed to run during hibernating - and resuming, and are used to support user interaction, storage access or the - like. Other kernel threads (those unneeded while hibernating) are frozen last. - This leaves us with userspace processes that need to be frozen. When a - process enters one of the *_sync system calls, we set a PF_SYNCTHREAD flag on - that process for the duration of that call. Processes that have this flag are - frozen after processes without it, so that we can seek to ensure that dirty - data is synced to disk as quickly as possible in a situation where other - processes may be submitting writes at the same time. Freezing the processes - that are submitting data stops new I/O from being submitted. Syncthreads can - then cleanly finish their work. So the order is: - - - Userspace processes without PF_SYNCTHREAD or PF_NOFREEZE; - - Userspace processes with PF_SYNCTHREAD (they won't have NOFREEZE); - - Kernel processes without PF_NOFREEZE. - - b. Eating memory. - - For a successful hibernation cycle, you need to have enough disk space to store the - image and enough memory for the various limitations of TuxOnIce's - algorithm. You can also specify a maximum image size. In order to attain - to those constraints, TuxOnIce may 'eat' memory. If, after freezing - processes, the constraints aren't met, TuxOnIce will thaw all the - other processes and begin to eat memory until its calculations indicate - the constraints are met. It will then freeze processes again and recheck - its calculations. - - c. Allocation of storage. - - Next, TuxOnIce allocates the storage that will be used to save - the image. - - The core of TuxOnIce knows nothing about how or where pages are stored. We - therefore request the active allocator (remember you might have compiled in - more than one!) to allocate enough storage for our expect image size. If - this request cannot be fulfilled, we eat more memory and try again. If it - is fulfiled, we seek to allocate additional storage, just in case our - expected compression ratio (if any) isn't achieved. This time, however, we - just continue if we can't allocate enough storage. - - If these calls to our allocator change the characteristics of the image - such that we haven't allocated enough memory, we also loop. (The allocator - may well need to allocate space for its storage information). - - d. Write the first part of the image. - - TuxOnIce stores the image in two sets of pages called 'pagesets'. - Pageset 2 contains pages on the active and inactive lists; essentially - the page cache. Pageset 1 contains all other pages, including the kernel. - We use two pagesets for one important reason: We need to make an atomic copy - of the kernel to ensure consistency of the image. Without a second pageset, - that would limit us to an image that was at most half the amount of memory - available. Using two pagesets allows us to store a full image. Since pageset - 2 pages won't be needed in saving pageset 1, we first save pageset 2 pages. - We can then make our atomic copy of the remaining pages using both pageset 2 - pages and any other pages that are free. While saving both pagesets, we are - careful not to corrupt the image. Among other things, we use lowlevel block - I/O routines that don't change the pagecache contents. - - The next step, then, is writing pageset 2. - - e. Suspending drivers and storing processor context. - - Having written pageset2, TuxOnIce calls the power management functions to - notify drivers of the hibernation, and saves the processor state in preparation - for the atomic copy of memory we are about to make. - - f. Atomic copy. - - At this stage, everything else but the TuxOnIce code is halted. Processes - are frozen or idling, drivers are quiesced and have stored (ideally and where - necessary) their configuration in memory we are about to atomically copy. - In our lowlevel architecture specific code, we have saved the CPU state. - We can therefore now do our atomic copy before resuming drivers etc. - - g. Save the atomic copy (pageset 1). - - TuxOnice can then write the atomic copy of the remaining pages. Since we - have copied the pages into other locations, we can continue to use the - normal block I/O routines without fear of corruption our image. - - f. Save the image header. - - Nearly there! We save our settings and other parameters needed for - reloading pageset 1 in an 'image header'. We also tell our allocator to - serialise its data at this stage, so that it can reread the image at resume - time. - - g. Set the image header. - - Finally, we edit the header at our resume= location. The signature is - changed by the allocator to reflect the fact that an image exists, and to - point to the start of that data if necessary (swap allocator). - - h. Power down. - - Or reboot if we're debugging and the appropriate option is selected. - - Whew! - - Reloading the image. - -------------------- - - Reloading the image is essentially the reverse of all the above. We load - our copy of pageset 1, being careful to choose locations that aren't going - to be overwritten as we copy it back (We start very early in the boot - process, so there are no other processes to quiesce here). We then copy - pageset 1 back to its original location in memory and restore the process - context. We are now running with the original kernel. Next, we reload the - pageset 2 pages, free the memory and swap used by TuxOnIce, restore - the pageset header and restart processes. Sounds easy in comparison to - hibernating, doesn't it! - - There is of course more to TuxOnIce than this, but this explanation - should be a good start. If there's interest, I'll write further - documentation on range pages and the low level I/O. - -11. Who wrote TuxOnIce? - - (Answer based on the writings of Florent Chabaud, credits in files and - Nigel's limited knowledge; apologies to anyone missed out!) - - The main developers of TuxOnIce have been... - - Gabor Kuti - Pavel Machek - Florent Chabaud - Bernard Blackham - Nigel Cunningham - - Significant portions of swsusp, the code in the vanilla kernel which - TuxOnIce enhances, have been worked on by Rafael Wysocki. Thanks should - also be expressed to him. - - The above mentioned developers have been aided in their efforts by a host - of hundreds, if not thousands of testers and people who have submitted bug - fixes & suggestions. Of special note are the efforts of Michael Frank, who - had his computers repetitively hibernate and resume for literally tens of - thousands of cycles and developed scripts to stress the system and test - TuxOnIce far beyond the point most of us (Nigel included!) would consider - testing. His efforts have contributed as much to TuxOnIce as any of the - names above. |