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journal: coalesce ftruncate()s in 250ms windows
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Prior to this change every journal append causes an ftruncate() for the
sake of inotify propagation of the mmap-based writes.
With this change the notification is deferred up to ~250ms, coalescing
any repeated journal writes during the deferred period into a single
ftruncate(). The ftruncate() call isn't free and doing it on every
append adds unnecessary overhead and latency in the journald event loop.
Introduces journal_file_enable_post_change_timer() which manages a
timer on the provided sd-event instance for scheduling coalesced
ftruncates. The ftruncate() behavior is unchanged unless
journal_file_enable_post_change_timer() is called on the JournalFile.
While not a tremendous improvement, profiling systemd-journald event loop
latencies using instrumentation as introduced by 34b8751 it was observed that
coalescing the ftruncates was low-hanging fruit worth pursuing.
Note orders 12 and 13 shifting left into order 11 and order 6 dipping into
order 5:
Unmodified:
log2(us) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
-----------------------------------------------------------
[10685.414572] 0 0 0 0 38 602 61 2 290 60 1643 2554 13 1 4 1 0 0 1
[10690.415114] 0 0 0 0 0 646 54 7 309 44 2073 2148 17 1 3 0 0 0 1
[10695.415509] 0 0 0 0 1 650 73 3 324 37 2071 2270 9 0 0 1 0 1 0
[10700.416297] 0 0 0 0 0 659 50 4 318 38 2111 2152 6 0 1 0 0 1 1
[10705.417136] 0 0 0 0 2 660 48 4 320 38 2129 2146 12 1 1 0 0 1 1
[10710.489114] 0 0 0 0 0 673 38 3 321 37 1925 2339 7 0 0 0 0 1 1
[10715.489613] 0 0 0 0 3 656 64 8 317 48 2365 2007 7 0 0 0 0 0 1
Coalesced:
log2(us) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19
-----------------------------------------------------------
[ 6169.161360] 0 0 0 1 24 786 54 11 389 24 4192 771 6 4 0 0 1 0 1
[ 6174.161705] 0 0 0 1 18 800 35 6 380 27 3977 893 3 1 0 0 1 0 1
[ 6179.162741] 0 0 0 1 28 768 51 4 391 16 3998 831 5 3 0 0 0 0 2
[ 6184.162856] 0 0 0 0 19 770 60 2 376 26 3795 1004 9 5 1 0 1 0 1
[ 6189.163279] 0 0 0 0 28 761 49 7 372 27 3729 1056 3 2 0 0 1 0 1
[ 6194.164255] 0 0 0 0 25 785 49 7 394 19 3996 908 6 3 2 0 0 0 1
[ 6199.164658] 0 0 0 0 29 797 35 5 389 18 3995 898 3 4 1 1 1 0 1
The remaining high-order delays are a result of the synchronous fsyncs in
systemd-journald, beyond the scope of this commit.
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Journal decompression fixes
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compress_blob took src, src_size, dst and *dst_size, but dst_size
wasn't used as an input parameter with the size of dst, but only as an
output parameter. dst was implicitly assumed to be at least src_size-1.
This code wasn't *wrong*, because the only real caller in
journal-file.c got it right. But it was misleading, and the tests in
test-compress.c got it wrong, and worked only because the output
buffer happened to be the same size as input buffer. So add a seperate
dst_allocated_size parameter to make it explicit what the size of the
buffer is, and to allow test to proceed with different output buffer
sizes.
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destructors
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For low end embedded systems 4 MiB for each journal file is a lot of
memory. Journald will use at least 512 KiB even if JOURNAL_FILE_SIZE_MIN is
set to less than that so just use 512 KiB.
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When reading stuff, we should only return EIO when an actual read error
occured, not when we don't like the data for whatever reason.
We already return ENODATA for all other kinds of file truncation, hence
do the same for the most obvious kind, so that callers know what ENODATA
means.
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Various changes to src/basic/
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There are more than enough to deserve their own .c file, hence move them
over.
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string-util.[ch]
There are more than enough calls doing string manipulations to deserve
its own files, hence do something about it.
This patch also sorts the #include blocks of all files that needed to be
updated, according to the sorting suggestions from CODING_STYLE. Since
pretty much every file needs our string manipulation functions this
effectively means that most files have sorted #include blocks now.
Also touches a few unrelated include files.
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Let's make sure we handle compression errors properly, and don't
misunderstand an error for success.
Also, let's actually compress things if lz4 is enabled.
Fixes #1662.
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Implement a maximum limit on number of journal files to keep around.
Enforcing a limit is useful on this since our performance when viewing
pays a heavy penalty for each journal file to interleve. This setting is
turned on now by default, and set to 100.
Also, actully implement what 348ced909724a1331b85d57aede80a102a00e428
promised: use whatever we find on disk at startup as lower bound on how
much disk space we can use. That commit introduced some provisions to
implement this, but actually never did.
This also adds "journalctl --vacuum-files=" to vacuum files on disk by
their number explicitly.
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Indicate that we are ignoring errors, when we ignore them, and log that
at LOG_WARNING level.
Use the right error code for the log message.
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The way it is customary everywhere else in our sources.
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off_t is a really weird type as it is usually 64bit these days (at least
in sane programs), but could theoretically be 32bit. We don't support
off_t as 32bit builds though, but still constantly deal with safely
converting from off_t to other types and back for no point.
Hence, never use the type anymore. Always use uint64_t instead. This has
various benefits, including that we can expose these values directly as
D-Bus properties, and also that the values parse the same in all cases.
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The function "free" is documented in the way that no action shall occur for
a passed null pointer. It is therefore not needed that a function caller
repeats a corresponding check.
http://stackoverflow.com/questions/18775608/free-a-null-pointer-anyway-or-check-first
This issue was fixed by using the software Coccinelle 1.0.1.
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When a new journal file is created we write the header first, then sync
and only then create the data and field hash tables in them. That means
to other processes it might appear that the files have a valid header
but not data and field hash tables. Our reader code should be able to
deal with this.
With this change we'll not map the two hash tables right-away after
opening a file for reading anymore (because that will of course fail if
the objects are missing), but delay this until the first time we access
them. On top of that, when we want to look something up in the hash
tables and we notice they aren't initialized yet, we consider them
empty.
This improves handling of some journal files reported in #487.
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This way users have the freedom to set or unset the FS_NOCOW_FL flag on
their journal files by setting it on the journal directory. Since our
default tmpfiles configuration now sets this flag on the directory the
flag is set by default on new files, however people can opt-out of this
by masking the tmpfiles file for it.
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like:
src/shared/install.c: In function ‘unit_file_lookup_state’:
src/shared/install.c:1861:16: warning: ‘r’ may be used uninitialized in
this function [-Wmaybe-uninitialized]
return r < 0 ? r : state;
^
src/shared/install.c:1796:13: note: ‘r’ was declared here
int r;
^
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Introduced in fa6ac76083b8ff.
Might be related to CID #1261724, but I don't know if coverity can
recurse this deep.
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Logs constantly show
systemd-journald[395]: Failed to set file attributes: Inappropriate ioctl for device
This is because ext4 does not support FS_NOCOW_FL.
[zj: fold into one conditional as suggested on the ML and
fix (preexisting) r/errno confusion in error message.]
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Commit 668c965af "journal: skipping of exhausted journal files is bad if
direction changed" fixed a correctness issue, but it also significantly
limited the cases where the optimization that skips exhausted journal
files could apply.
As a result, some journalctl queries are much slower in v219 than in v218.
(e.g. queries where a "--since" cutoff should have quickly eliminated
older journal files from consideration, but didn't.)
If already in the initial iteration find_location_with_matches() finds
no entry, the journal file's location is not updated. This is fine,
except that:
- We must update at least f->last_direction. The optimization relies on
it. Let's separate that from journal_file_save_location() and update
it immediately after the direction checks.
- The optimization was conditional on "f->current_offset > 0", but it
would always be 0 in this scenario. This check is unnecessary for the
optimization.
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This patch removes includes that are not used. The removals were found with
include-what-you-use which checks if any of the symbols from a header is
in use.
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Leave it to the compiler to figure out whether it shall inline stuff or
not.
Only place where using static inline is OK to use is in in header
files, really.
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fd_setcrtime()
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btrfs' COW logic results in heavily fragment journal files, which is
detrimental for perfomance. Hence, turn off COW for journal files as we
create them.
Turning off COW comes at the cost of data integrity guarantees, but this
should be acceptable, given that we do our own checksumming, and
generally have a pretty conservative write pattern.
Also see discussion on linux-btrfs:
http://www.spinics.net/lists/linux-btrfs/msg41001.html
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Our write pattern is quite awful for CoW file systems (btrfs...), as we
keep updating file parts in the beginning of the file. This results in
fragmented journal files. Hence: when rotating files, defragment them,
since at that point we know that no further write accesses will be made.
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deleted, rotate
https://bugzilla.redhat.com/show_bug.cgi?id=1171719
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journal file headers
Since the file headers might be replaced by zeroed pages now due to
sigbus we should make sure we don't end up dividing by zero because we
don't check values read from journal file headers for changes.
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Even though we use fallocate() it appears that file systems like btrfs
will trigger SIGBUS on certain low-disk-space situation. We should
handle that, hence catch the signal, add it to a list of invalidated
pages, and replace the page with an empty memory area. After each write
check if SIGBUS was triggered, and consider the write invalid if it was.
This should make journald a lot more robust with file systems where
fallocate() is not reliable, for example all CoW file systems
(btrfs...), where changing written data can fail with disk full errors.
https://bugzilla.redhat.com/show_bug.cgi?id=1045810
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The current offset is sufficient information.
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When comparing the locations of candidate entries, we can rely on the
location information stored in struct JournalFile.
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In next_beyond_location() when we find a candidate entry in a journal
file, save its location information in struct JournalFile.
The purpose of remembering the locations of candidate entries is to be
able to save work in the next iteration. This patch does only the
remembering part.
LOCATION_SEEK means the location identifies a candidate entry.
When a winner is picked from among candidates, it becomes
LOCATION_DISCRETE.
LOCATION_TAIL here signifies we've iterated the file to the end (or the
beginning in the case of reversed direction).
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Its only caller is a test.
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try_context() is such a hot path that the hashmap lookup is expensive.
The number of contexts is small - it is the number of object types.
Using a hashmap is overkill. A plain array will do.
Before:
$ time ./journalctl --since=2014-06-01 --until=2014-07-01 > /dev/null
real 0m9.445s
user 0m9.228s
sys 0m0.213s
After:
$ time ./journalctl --since=2014-06-01 --until=2014-07-01 > /dev/null
real 0m5.438s
user 0m5.266s
sys 0m0.170s
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