diff options
Diffstat (limited to 'Documentation/vm')
| -rw-r--r-- | Documentation/vm/00-INDEX | 2 | ||||
| -rw-r--r-- | Documentation/vm/hugetlbpage.txt | 6 | ||||
| -rw-r--r-- | Documentation/vm/numa | 4 | ||||
| -rw-r--r-- | Documentation/vm/numa_memory_policy.txt | 2 | ||||
| -rw-r--r-- | Documentation/vm/page_migration | 110 | ||||
| -rw-r--r-- | Documentation/vm/page_owner.txt | 9 | ||||
| -rw-r--r-- | Documentation/vm/pagemap.txt | 2 | ||||
| -rw-r--r-- | Documentation/vm/slub.txt | 4 | ||||
| -rw-r--r-- | Documentation/vm/transhuge.txt | 166 | ||||
| -rw-r--r-- | Documentation/vm/uksm.txt | 60 | ||||
| -rw-r--r-- | Documentation/vm/unevictable-lru.txt | 23 | ||||
| -rw-r--r-- | Documentation/vm/z3fold.txt | 26 |
12 files changed, 354 insertions, 60 deletions
diff --git a/Documentation/vm/00-INDEX b/Documentation/vm/00-INDEX index 6a5e2a102..09eaa9a12 100644 --- a/Documentation/vm/00-INDEX +++ b/Documentation/vm/00-INDEX @@ -18,6 +18,8 @@ idle_page_tracking.txt - description of the idle page tracking feature. ksm.txt - how to use the Kernel Samepage Merging feature. +uksm.txt + - Introduction to Ultra KSM numa - information about NUMA specific code in the Linux vm. numa_memory_policy.txt diff --git a/Documentation/vm/hugetlbpage.txt b/Documentation/vm/hugetlbpage.txt index 54dd9b9c6..59cbc803a 100644 --- a/Documentation/vm/hugetlbpage.txt +++ b/Documentation/vm/hugetlbpage.txt @@ -220,7 +220,7 @@ resulting effect on persistent huge page allocation is as follows: node list of "all" with numactl --interleave or --membind [-m] to achieve interleaving over all nodes in the system or cpuset. -4) Any task mempolicy specifed--e.g., using numactl--will be constrained by +4) Any task mempolicy specified--e.g., using numactl--will be constrained by the resource limits of any cpuset in which the task runs. Thus, there will be no way for a task with non-default policy running in a cpuset with a subset of the system nodes to allocate huge pages outside the cpuset @@ -275,10 +275,10 @@ This command mounts a (pseudo) filesystem of type hugetlbfs on the directory options sets the owner and group of the root of the file system. By default the uid and gid of the current process are taken. The mode option sets the mode of root of file system to value & 01777. This value is given in octal. -By default the value 0755 is picked. If the paltform supports multiple huge +By default the value 0755 is picked. If the platform supports multiple huge page sizes, the pagesize option can be used to specify the huge page size and associated pool. pagesize is specified in bytes. If pagesize is not specified -the paltform's default huge page size and associated pool will be used. The +the platform's default huge page size and associated pool will be used. The size option sets the maximum value of memory (huge pages) allowed for that filesystem (/mnt/huge). The size option can be specified in bytes, or as a percentage of the specified huge page pool (nr_hugepages). The size is diff --git a/Documentation/vm/numa b/Documentation/vm/numa index ade012742..e0b58c0e6 100644 --- a/Documentation/vm/numa +++ b/Documentation/vm/numa @@ -63,7 +63,7 @@ nodes. Each emulated node will manage a fraction of the underlying cells' physical memory. NUMA emluation is useful for testing NUMA kernel and application features on non-NUMA platforms, and as a sort of memory resource management mechanism when used together with cpusets. -[see Documentation/cgroups/cpusets.txt] +[see Documentation/cgroup-v1/cpusets.txt] For each node with memory, Linux constructs an independent memory management subsystem, complete with its own free page lists, in-use page lists, usage @@ -113,7 +113,7 @@ allocation behavior using Linux NUMA memory policy. System administrators can restrict the CPUs and nodes' memories that a non- privileged user can specify in the scheduling or NUMA commands and functions -using control groups and CPUsets. [see Documentation/cgroups/cpusets.txt] +using control groups and CPUsets. [see Documentation/cgroup-v1/cpusets.txt] On architectures that do not hide memoryless nodes, Linux will include only zones [nodes] with memory in the zonelists. This means that for a memoryless diff --git a/Documentation/vm/numa_memory_policy.txt b/Documentation/vm/numa_memory_policy.txt index badb05076..622b92781 100644 --- a/Documentation/vm/numa_memory_policy.txt +++ b/Documentation/vm/numa_memory_policy.txt @@ -9,7 +9,7 @@ document attempts to describe the concepts and APIs of the 2.6 memory policy support. Memory policies should not be confused with cpusets -(Documentation/cgroups/cpusets.txt) +(Documentation/cgroup-v1/cpusets.txt) which is an administrative mechanism for restricting the nodes from which memory may be allocated by a set of processes. Memory policies are a programming interface that a NUMA-aware application can take advantage of. When diff --git a/Documentation/vm/page_migration b/Documentation/vm/page_migration index fea5c0864..0478ae2ad 100644 --- a/Documentation/vm/page_migration +++ b/Documentation/vm/page_migration @@ -38,7 +38,7 @@ locations. Larger installations usually partition the system using cpusets into sections of nodes. Paul Jackson has equipped cpusets with the ability to move pages when a task is moved to another cpuset (See -Documentation/cgroups/cpusets.txt). +Documentation/cgroup-v1/cpusets.txt). Cpusets allows the automation of process locality. If a task is moved to a new cpuset then also all its pages are moved with it so that the performance of the process does not sink dramatically. Also the pages @@ -142,5 +142,111 @@ Steps: 20. The new page is moved to the LRU and can be scanned by the swapper etc again. -Christoph Lameter, May 8, 2006. +C. Non-LRU page migration +------------------------- + +Although original migration aimed for reducing the latency of memory access +for NUMA, compaction who want to create high-order page is also main customer. + +Current problem of the implementation is that it is designed to migrate only +*LRU* pages. However, there are potential non-lru pages which can be migrated +in drivers, for example, zsmalloc, virtio-balloon pages. + +For virtio-balloon pages, some parts of migration code path have been hooked +up and added virtio-balloon specific functions to intercept migration logics. +It's too specific to a driver so other drivers who want to make their pages +movable would have to add own specific hooks in migration path. + +To overclome the problem, VM supports non-LRU page migration which provides +generic functions for non-LRU movable pages without driver specific hooks +migration path. + +If a driver want to make own pages movable, it should define three functions +which are function pointers of struct address_space_operations. + +1. bool (*isolate_page) (struct page *page, isolate_mode_t mode); + +What VM expects on isolate_page function of driver is to return *true* +if driver isolates page successfully. On returing true, VM marks the page +as PG_isolated so concurrent isolation in several CPUs skip the page +for isolation. If a driver cannot isolate the page, it should return *false*. + +Once page is successfully isolated, VM uses page.lru fields so driver +shouldn't expect to preserve values in that fields. + +2. int (*migratepage) (struct address_space *mapping, + struct page *newpage, struct page *oldpage, enum migrate_mode); + +After isolation, VM calls migratepage of driver with isolated page. +The function of migratepage is to move content of the old page to new page +and set up fields of struct page newpage. Keep in mind that you should +indicate to the VM the oldpage is no longer movable via __ClearPageMovable() +under page_lock if you migrated the oldpage successfully and returns +MIGRATEPAGE_SUCCESS. If driver cannot migrate the page at the moment, driver +can return -EAGAIN. On -EAGAIN, VM will retry page migration in a short time +because VM interprets -EAGAIN as "temporal migration failure". On returning +any error except -EAGAIN, VM will give up the page migration without retrying +in this time. + +Driver shouldn't touch page.lru field VM using in the functions. + +3. void (*putback_page)(struct page *); + +If migration fails on isolated page, VM should return the isolated page +to the driver so VM calls driver's putback_page with migration failed page. +In this function, driver should put the isolated page back to the own data +structure. +4. non-lru movable page flags + +There are two page flags for supporting non-lru movable page. + +* PG_movable + +Driver should use the below function to make page movable under page_lock. + + void __SetPageMovable(struct page *page, struct address_space *mapping) + +It needs argument of address_space for registering migration family functions +which will be called by VM. Exactly speaking, PG_movable is not a real flag of +struct page. Rather than, VM reuses page->mapping's lower bits to represent it. + + #define PAGE_MAPPING_MOVABLE 0x2 + page->mapping = page->mapping | PAGE_MAPPING_MOVABLE; + +so driver shouldn't access page->mapping directly. Instead, driver should +use page_mapping which mask off the low two bits of page->mapping under +page lock so it can get right struct address_space. + +For testing of non-lru movable page, VM supports __PageMovable function. +However, it doesn't guarantee to identify non-lru movable page because +page->mapping field is unified with other variables in struct page. +As well, if driver releases the page after isolation by VM, page->mapping +doesn't have stable value although it has PAGE_MAPPING_MOVABLE +(Look at __ClearPageMovable). But __PageMovable is cheap to catch whether +page is LRU or non-lru movable once the page has been isolated. Because +LRU pages never can have PAGE_MAPPING_MOVABLE in page->mapping. It is also +good for just peeking to test non-lru movable pages before more expensive +checking with lock_page in pfn scanning to select victim. + +For guaranteeing non-lru movable page, VM provides PageMovable function. +Unlike __PageMovable, PageMovable functions validates page->mapping and +mapping->a_ops->isolate_page under lock_page. The lock_page prevents sudden +destroying of page->mapping. + +Driver using __SetPageMovable should clear the flag via __ClearMovablePage +under page_lock before the releasing the page. + +* PG_isolated + +To prevent concurrent isolation among several CPUs, VM marks isolated page +as PG_isolated under lock_page. So if a CPU encounters PG_isolated non-lru +movable page, it can skip it. Driver doesn't need to manipulate the flag +because VM will set/clear it automatically. Keep in mind that if driver +sees PG_isolated page, it means the page have been isolated by VM so it +shouldn't touch page.lru field. +PG_isolated is alias with PG_reclaim flag so driver shouldn't use the flag +for own purpose. + +Christoph Lameter, May 8, 2006. +Minchan Kim, Mar 28, 2016. diff --git a/Documentation/vm/page_owner.txt b/Documentation/vm/page_owner.txt index 8f3ce9b3a..ffff14390 100644 --- a/Documentation/vm/page_owner.txt +++ b/Documentation/vm/page_owner.txt @@ -28,10 +28,11 @@ with page owner and page owner is disabled in runtime due to no enabling boot option, runtime overhead is marginal. If disabled in runtime, it doesn't require memory to store owner information, so there is no runtime memory overhead. And, page owner inserts just two unlikely branches into -the page allocator hotpath and if it returns false then allocation is -done like as the kernel without page owner. These two unlikely branches -would not affect to allocation performance. Following is the kernel's -code size change due to this facility. +the page allocator hotpath and if not enabled, then allocation is done +like as the kernel without page owner. These two unlikely branches should +not affect to allocation performance, especially if the static keys jump +label patching functionality is available. Following is the kernel's code +size change due to this facility. - Without page owner text data bss dec hex filename diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt index 0e1e55588..eafcefa15 100644 --- a/Documentation/vm/pagemap.txt +++ b/Documentation/vm/pagemap.txt @@ -62,7 +62,7 @@ There are four components to pagemap: 14. SWAPBACKED 15. COMPOUND_HEAD 16. COMPOUND_TAIL - 16. HUGE + 17. HUGE 18. UNEVICTABLE 19. HWPOISON 20. NOPAGE diff --git a/Documentation/vm/slub.txt b/Documentation/vm/slub.txt index f0d340959..84652419b 100644 --- a/Documentation/vm/slub.txt +++ b/Documentation/vm/slub.txt @@ -35,8 +35,8 @@ slub_debug=<Debug-Options>,<slab name> Enable options only for select slabs Possible debug options are - F Sanity checks on (enables SLAB_DEBUG_FREE. Sorry - SLAB legacy issues) + F Sanity checks on (enables SLAB_DEBUG_CONSISTENCY_CHECKS + Sorry SLAB legacy issues) Z Red zoning P Poisoning (object and padding) U User tracking (free and alloc) diff --git a/Documentation/vm/transhuge.txt b/Documentation/vm/transhuge.txt index 21cf34f3d..2ec6adb5a 100644 --- a/Documentation/vm/transhuge.txt +++ b/Documentation/vm/transhuge.txt @@ -9,8 +9,8 @@ using huge pages for the backing of virtual memory with huge pages that supports the automatic promotion and demotion of page sizes and without the shortcomings of hugetlbfs. -Currently it only works for anonymous memory mappings but in the -future it can expand over the pagecache layer starting with tmpfs. +Currently it only works for anonymous memory mappings and tmpfs/shmem. +But in the future it can expand to other filesystems. The reason applications are running faster is because of two factors. The first factor is almost completely irrelevant and it's not @@ -57,10 +57,6 @@ miss is going to run faster. feature that applies to all dynamic high order allocations in the kernel) -- this initial support only offers the feature in the anonymous memory - regions but it'd be ideal to move it to tmpfs and the pagecache - later - Transparent Hugepage Support maximizes the usefulness of free memory if compared to the reservation approach of hugetlbfs by allowing all unused memory to be used as cache or other movable (or even unmovable @@ -94,31 +90,48 @@ madvise(MADV_HUGEPAGE) on their critical mmapped regions. == sysfs == -Transparent Hugepage Support can be entirely disabled (mostly for -debugging purposes) or only enabled inside MADV_HUGEPAGE regions (to -avoid the risk of consuming more memory resources) or enabled system -wide. This can be achieved with one of: +Transparent Hugepage Support for anonymous memory can be entirely disabled +(mostly for debugging purposes) or only enabled inside MADV_HUGEPAGE +regions (to avoid the risk of consuming more memory resources) or enabled +system wide. This can be achieved with one of: echo always >/sys/kernel/mm/transparent_hugepage/enabled echo madvise >/sys/kernel/mm/transparent_hugepage/enabled echo never >/sys/kernel/mm/transparent_hugepage/enabled It's also possible to limit defrag efforts in the VM to generate -hugepages in case they're not immediately free to madvise regions or -to never try to defrag memory and simply fallback to regular pages -unless hugepages are immediately available. Clearly if we spend CPU -time to defrag memory, we would expect to gain even more by the fact -we use hugepages later instead of regular pages. This isn't always +anonymous hugepages in case they're not immediately free to madvise +regions or to never try to defrag memory and simply fallback to regular +pages unless hugepages are immediately available. Clearly if we spend CPU +time to defrag memory, we would expect to gain even more by the fact we +use hugepages later instead of regular pages. This isn't always guaranteed, but it may be more likely in case the allocation is for a MADV_HUGEPAGE region. echo always >/sys/kernel/mm/transparent_hugepage/defrag +echo defer >/sys/kernel/mm/transparent_hugepage/defrag echo madvise >/sys/kernel/mm/transparent_hugepage/defrag echo never >/sys/kernel/mm/transparent_hugepage/defrag -By default kernel tries to use huge zero page on read page fault. -It's possible to disable huge zero page by writing 0 or enable it -back by writing 1: +"always" means that an application requesting THP will stall on allocation +failure and directly reclaim pages and compact memory in an effort to +allocate a THP immediately. This may be desirable for virtual machines +that benefit heavily from THP use and are willing to delay the VM start +to utilise them. + +"defer" means that an application will wake kswapd in the background +to reclaim pages and wake kcompact to compact memory so that THP is +available in the near future. It's the responsibility of khugepaged +to then install the THP pages later. + +"madvise" will enter direct reclaim like "always" but only for regions +that are have used madvise(MADV_HUGEPAGE). This is the default behaviour. + +"never" should be self-explanatory. + +By default kernel tries to use huge zero page on read page fault to +anonymous mapping. It's possible to disable huge zero page by writing 0 +or enable it back by writing 1: echo 0 >/sys/kernel/mm/transparent_hugepage/use_zero_page echo 1 >/sys/kernel/mm/transparent_hugepage/use_zero_page @@ -187,21 +200,67 @@ Support by passing the parameter "transparent_hugepage=always" or "transparent_hugepage=madvise" or "transparent_hugepage=never" (without "") to the kernel command line. +== Hugepages in tmpfs/shmem == + +You can control hugepage allocation policy in tmpfs with mount option +"huge=". It can have following values: + + - "always": + Attempt to allocate huge pages every time we need a new page; + + - "never": + Do not allocate huge pages; + + - "within_size": + Only allocate huge page if it will be fully within i_size. + Also respect fadvise()/madvise() hints; + + - "advise: + Only allocate huge pages if requested with fadvise()/madvise(); + +The default policy is "never". + +"mount -o remount,huge= /mountpoint" works fine after mount: remounting +huge=never will not attempt to break up huge pages at all, just stop more +from being allocated. + +There's also sysfs knob to control hugepage allocation policy for internal +shmem mount: /sys/kernel/mm/transparent_hugepage/shmem_enabled. The mount +is used for SysV SHM, memfds, shared anonymous mmaps (of /dev/zero or +MAP_ANONYMOUS), GPU drivers' DRM objects, Ashmem. + +In addition to policies listed above, shmem_enabled allows two further +values: + + - "deny": + For use in emergencies, to force the huge option off from + all mounts; + - "force": + Force the huge option on for all - very useful for testing; + == Need of application restart == -The transparent_hugepage/enabled values only affect future -behavior. So to make them effective you need to restart any -application that could have been using hugepages. This also applies to -the regions registered in khugepaged. +The transparent_hugepage/enabled values and tmpfs mount option only affect +future behavior. So to make them effective you need to restart any +application that could have been using hugepages. This also applies to the +regions registered in khugepaged. == Monitoring usage == -The number of transparent huge pages currently used by the system is -available by reading the AnonHugePages field in /proc/meminfo. To -identify what applications are using transparent huge pages, it is -necessary to read /proc/PID/smaps and count the AnonHugePages fields -for each mapping. Note that reading the smaps file is expensive and -reading it frequently will incur overhead. +The number of anonymous transparent huge pages currently used by the +system is available by reading the AnonHugePages field in /proc/meminfo. +To identify what applications are using anonymous transparent huge pages, +it is necessary to read /proc/PID/smaps and count the AnonHugePages fields +for each mapping. + +The number of file transparent huge pages mapped to userspace is available +by reading ShmemPmdMapped and ShmemHugePages fields in /proc/meminfo. +To identify what applications are mapping file transparent huge pages, it +is necessary to read /proc/PID/smaps and count the FileHugeMapped fields +for each mapping. + +Note that reading the smaps file is expensive and reading it +frequently will incur overhead. There are a number of counters in /proc/vmstat that may be used to monitor how successfully the system is providing huge pages for use. @@ -221,6 +280,12 @@ thp_collapse_alloc_failed is incremented if khugepaged found a range of pages that should be collapsed into one huge page but failed the allocation. +thp_file_alloc is incremented every time a file huge page is successfully +i allocated. + +thp_file_mapped is incremented every time a file huge page is mapped into + user address space. + thp_split_page is incremented every time a huge page is split into base pages. This can happen for a variety of reasons but a common reason is that a huge page is old and is being reclaimed. @@ -229,6 +294,11 @@ thp_split_page is incremented every time a huge page is split into base thp_split_page_failed is is incremented if kernel fails to split huge page. This can happen if the page was pinned by somebody. +thp_deferred_split_page is incremented when a huge page is put onto split + queue. This happens when a huge page is partially unmapped and + splitting it would free up some memory. Pages on split queue are + going to be split under memory pressure. + thp_split_pmd is incremented every time a PMD split into table of PTEs. This can happen, for instance, when application calls mprotect() or munmap() on part of huge page. It doesn't split huge page, only @@ -318,7 +388,7 @@ unaffected. libhugetlbfs will also work fine as usual. == Graceful fallback == -Code walking pagetables but unware about huge pmds can simply call +Code walking pagetables but unaware about huge pmds can simply call split_huge_pmd(vma, pmd, addr) where the pmd is the one returned by pmd_offset. It's trivial to make the code transparent hugepage aware by just grepping for "pmd_offset" and adding split_huge_pmd where @@ -372,28 +442,36 @@ hugepage natively. Once finished you can drop the page table lock. Refcounting on THP is mostly consistent with refcounting on other compound pages: - - get_page()/put_page() and GUP operate in head page's ->_count. + - get_page()/put_page() and GUP operate in head page's ->_refcount. - - ->_count in tail pages is always zero: get_page_unless_zero() never + - ->_refcount in tail pages is always zero: get_page_unless_zero() never succeed on tail pages. - map/unmap of the pages with PTE entry increment/decrement ->_mapcount on relevant sub-page of the compound page. - map/unmap of the whole compound page accounted in compound_mapcount - (stored in first tail page). + (stored in first tail page). For file huge pages, we also increment + ->_mapcount of all sub-pages in order to have race-free detection of + last unmap of subpages. -PageDoubleMap() indicates that ->_mapcount in all subpages is offset up by one. -This additional reference is required to get race-free detection of unmap of -subpages when we have them mapped with both PMDs and PTEs. +PageDoubleMap() indicates that the page is *possibly* mapped with PTEs. + +For anonymous pages PageDoubleMap() also indicates ->_mapcount in all +subpages is offset up by one. This additional reference is required to +get race-free detection of unmap of subpages when we have them mapped with +both PMDs and PTEs. This is optimization required to lower overhead of per-subpage mapcount tracking. The alternative is alter ->_mapcount in all subpages on each map/unmap of the whole compound page. -We set PG_double_map when a PMD of the page got split for the first time, -but still have PMD mapping. The addtional references go away with last -compound_mapcount. +For anonymous pages, we set PG_double_map when a PMD of the page got split +for the first time, but still have PMD mapping. The additional references +go away with last compound_mapcount. + +File pages get PG_double_map set on first map of the page with PTE and +goes away when the page gets evicted from page cache. split_huge_page internally has to distribute the refcounts in the head page to the tail pages before clearing all PG_head/tail bits from the page @@ -404,16 +482,16 @@ requests to split pinned huge page: it expects page count to be equal to sum of mapcount of all sub-pages plus one (split_huge_page caller must have reference for head page). -split_huge_page uses migration entries to stabilize page->_count and -page->_mapcount. +split_huge_page uses migration entries to stabilize page->_refcount and +page->_mapcount of anonymous pages. File pages just got unmapped. We safe against physical memory scanners too: the only legitimate way scanner can get reference to a page is get_page_unless_zero(). -All tail pages has zero ->_count until atomic_add(). It prevent scanner -from geting reference to tail page up to the point. After the atomic_add() -we don't care about ->_count value. We already known how many references -with should uncharge from head page. +All tail pages have zero ->_refcount until atomic_add(). This prevents the +scanner from getting a reference to the tail page up to that point. After the +atomic_add() we don't care about the ->_refcount value. We already known how +many references should be uncharged from the head page. For head page get_page_unless_zero() will succeed and we don't mind. It's clear where reference should go after split: it will stay on head page. diff --git a/Documentation/vm/uksm.txt b/Documentation/vm/uksm.txt new file mode 100644 index 000000000..8fce86f0c --- /dev/null +++ b/Documentation/vm/uksm.txt @@ -0,0 +1,60 @@ +The Ultra Kernel Samepage Merging feature +---------------------------------------------- +/* + * Ultra KSM. Copyright (C) 2011-2012 Nai Xia + * + * This is an improvement upon KSM. Some basic data structures and routines + * are borrowed from ksm.c . + * + * Its new features: + * 1. Full system scan: + * It automatically scans all user processes' anonymous VMAs. Kernel-user + * interaction to submit a memory area to KSM is no longer needed. + * + * 2. Rich area detection: + * It automatically detects rich areas containing abundant duplicated + * pages based. Rich areas are given a full scan speed. Poor areas are + * sampled at a reasonable speed with very low CPU consumption. + * + * 3. Ultra Per-page scan speed improvement: + * A new hash algorithm is proposed. As a result, on a machine with + * Core(TM)2 Quad Q9300 CPU in 32-bit mode and 800MHZ DDR2 main memory, it + * can scan memory areas that does not contain duplicated pages at speed of + * 627MB/sec ~ 2445MB/sec and can merge duplicated areas at speed of + * 477MB/sec ~ 923MB/sec. + * + * 4. Thrashing area avoidance: + * Thrashing area(an VMA that has frequent Ksm page break-out) can be + * filtered out. My benchmark shows it's more efficient than KSM's per-page + * hash value based volatile page detection. + * + * + * 5. Misc changes upon KSM: + * * It has a fully x86-opitmized memcmp dedicated for 4-byte-aligned page + * comparison. It's much faster than default C version on x86. + * * rmap_item now has an struct *page member to loosely cache a + * address-->page mapping, which reduces too much time-costly + * follow_page(). + * * The VMA creation/exit procedures are hooked to let the Ultra KSM know. + * * try_to_merge_two_pages() now can revert a pte if it fails. No break_ + * ksm is needed for this case. + * + * 6. Full Zero Page consideration(contributed by Figo Zhang) + * Now uksmd consider full zero pages as special pages and merge them to an + * special unswappable uksm zero page. + */ + +ChangeLog: + +2012-05-05 The creation of this Doc +2012-05-08 UKSM 0.1.1.1 libc crash bug fix, api clean up, doc clean up. +2012-05-28 UKSM 0.1.1.2 bug fix release +2012-06-26 UKSM 0.1.2-beta1 first beta release for 0.1.2 +2012-07-2 UKSM 0.1.2-beta2 +2012-07-10 UKSM 0.1.2-beta3 +2012-07-26 UKSM 0.1.2 Fine grained speed control, more scan optimization. +2012-10-13 UKSM 0.1.2.1 Bug fixes. +2012-12-31 UKSM 0.1.2.2 Minor bug fixes. +2014-07-02 UKSM 0.1.2.3 Fix a " __this_cpu_read() in preemptible bug". +2015-04-22 UKSM 0.1.2.4 Fix a race condition that can sometimes trigger anonying warnings. +2016-09-10 UKSM 0.1.2.5 Fix a bug in dedup ratio calculation. diff --git a/Documentation/vm/unevictable-lru.txt b/Documentation/vm/unevictable-lru.txt index fa3b52708..e14718572 100644 --- a/Documentation/vm/unevictable-lru.txt +++ b/Documentation/vm/unevictable-lru.txt @@ -122,7 +122,7 @@ MEMORY CONTROL GROUP INTERACTION -------------------------------- The unevictable LRU facility interacts with the memory control group [aka -memory controller; see Documentation/cgroups/memory.txt] by extending the +memory controller; see Documentation/cgroup-v1/memory.txt] by extending the lru_list enum. The memory controller data structure automatically gets a per-zone unevictable @@ -461,6 +461,27 @@ unevictable LRU is enabled, the work of compaction is mostly handled by the page migration code and the same work flow as described in MIGRATING MLOCKED PAGES will apply. +MLOCKING TRANSPARENT HUGE PAGES +------------------------------- + +A transparent huge page is represented by a single entry on an LRU list. +Therefore, we can only make unevictable an entire compound page, not +individual subpages. + +If a user tries to mlock() part of a huge page, we want the rest of the +page to be reclaimable. + +We cannot just split the page on partial mlock() as split_huge_page() can +fail and new intermittent failure mode for the syscall is undesirable. + +We handle this by keeping PTE-mapped huge pages on normal LRU lists: the +PMD on border of VM_LOCKED VMA will be split into PTE table. + +This way the huge page is accessible for vmscan. Under memory pressure the +page will be split, subpages which belong to VM_LOCKED VMAs will be moved +to unevictable LRU and the rest can be reclaimed. + +See also comment in follow_trans_huge_pmd(). mmap(MAP_LOCKED) SYSTEM CALL HANDLING ------------------------------------- diff --git a/Documentation/vm/z3fold.txt b/Documentation/vm/z3fold.txt new file mode 100644 index 000000000..38e4dac81 --- /dev/null +++ b/Documentation/vm/z3fold.txt @@ -0,0 +1,26 @@ +z3fold +------ + +z3fold is a special purpose allocator for storing compressed pages. +It is designed to store up to three compressed pages per physical page. +It is a zbud derivative which allows for higher compression +ratio keeping the simplicity and determinism of its predecessor. + +The main differences between z3fold and zbud are: +* unlike zbud, z3fold allows for up to PAGE_SIZE allocations +* z3fold can hold up to 3 compressed pages in its page +* z3fold doesn't export any API itself and is thus intended to be used + via the zpool API. + +To keep the determinism and simplicity, z3fold, just like zbud, always +stores an integral number of compressed pages per page, but it can store +up to 3 pages unlike zbud which can store at most 2. Therefore the +compression ratio goes to around 2.7x while zbud's one is around 1.7x. + +Unlike zbud (but like zsmalloc for that matter) z3fold_alloc() does not +return a dereferenceable pointer. Instead, it returns an unsigned long +handle which encodes actual location of the allocated object. + +Keeping effective compression ratio close to zsmalloc's, z3fold doesn't +depend on MMU enabled and provides more predictable reclaim behavior +which makes it a better fit for small and response-critical systems. |