linux.git/mm/page-writeback.c, branch v2.6.31

Fix congestion_wait() sync/async vs read/write confusion

2009-07-10T18:31:53+00:00

Commit 1faa16d22877f4839bd433547d770c676d1d964c accidentally broke
the bdi congestion wait queue logic, causing us to wait on congestion
for WRITE (== 1) when we really wanted BLK_RW_ASYNC (== 0) instead.

Signed-off-by: Jens Axboe

mm: prevent balance_dirty_pages() from doing too much work

2009-07-01T01:56:01+00:00

balance_dirty_pages can overreact and move all of the dirty pages to
writeback unnecessarily.

balance_dirty_pages makes its decision to throttle based on the number of
dirty plus writeback pages that are over the calculated limit,so it will
continue to move pages even when there are plenty of pages in writeback
and less than the threshold still dirty.

This allows it to overshoot its limits and move all the dirty pages to
writeback while waiting for the drives to catch up and empty the writeback
list.

A simple fio test easily demonstrates this problem.

fio --name=f1 --directory=/disk1 --size=2G -rw=write --name=f2 --directory=/disk2 --size=1G --rw=write --startdelay=10

This is the simplest fix I could find, but I'm not entirely sure that it
alone will be enough for all cases.  But it certainly is an improvement on
my desktop machine writing to 2 disks.

Do we need something more for machines with large arrays where
bdi_threshold * number_of_drives is greater than the dirty_ratio ?

Signed-off-by: Richard Kennedy 
Acked-by: Peter Zijlstra 
Cc: Jens Axboe 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm/page-writeback.c: dirty limit type should be unsigned long

2009-06-17T02:47:31+00:00

get_dirty_limits() calls clip_bdi_dirty_limit() and task_dirty_limit()
with variable pbdi_dirty as one of the arguments.  This variable is an
unsigned long * but both functions expect it to be a long *.  This causes
the following sparse warnings:

  warning: incorrect type in argument 3 (different signedness)
     expected long *pbdi_dirty
     got unsigned long *pbdi_dirty
  warning: incorrect type in argument 2 (different signedness)
     expected long *pdirty
     got unsigned long *pbdi_dirty

Fix the warnings by changing the long * to unsigned long * in both
functions.

Signed-off-by: H Hartley Sweeten 
Cc: Johannes Weiner 
Cc: Peter Zijlstra 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

page-writeback: fix the calculation of the oldest_jif in wb_kupdate()

2009-05-17T23:36:11+00:00

wb_kupdate() function has a bug on linux-2.6.30-rc5.  This bug causes
generic_sync_sb_inodes() to start to write inodes back much earlier than
our expectations because it miscalculates oldest_jif in wb_kupdate().

This bug was introduced in 704503d836042d4a4c7685b7036e7de0418fbc0f
('mm: fix proc_dointvec_userhz_jiffies "breakage"').

Signed-off-by: Toshiyuki Okajima 
Cc: Alexey Dobriyan 
Cc: Peter Zijlstra 
Cc: Nick Piggin 
Cc: Al Viro 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

mm: fix proc_dointvec_userhz_jiffies "breakage"

2009-04-01T15:59:13+00:00

Addresses http://bugzilla.kernel.org/show_bug.cgi?id=9838

On i386, HZ=1000, jiffies_to_clock_t() converts time in a somewhat strange
way from the user's point of view:

	# echo 500 >/proc/sys/vm/dirty_writeback_centisecs
	# cat /proc/sys/vm/dirty_writeback_centisecs
	499

So, we have 5000 jiffies converted to only 499 clock ticks and reported
back.

TICK_NSEC = 999848
ACTHZ = 256039

Keeping in-kernel variable in units passed from userspace will fix issue
of course, but this probably won't be right for every sysctl.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Alexey Dobriyan 
Cc: Peter Zijlstra 
Cc: Nick Piggin 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

vfs: add/use account_page_dirtied()

2009-04-01T15:59:12+00:00

Add a helper function account_page_dirtied().  Use that from two
callsites.  reiser4 adds a function which adds a third callsite.

Signed-off-by: Edward Shishkin
Cc: Nick Piggin 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

writeback: double the dirty thresholds

2009-03-26T18:01:11+00:00

Enlarge default dirty ratios from 5/10 to 10/20.  This fixes [Bug
#12809] iozone regression with 2.6.29-rc6.

The iozone benchmarks are performed on a 1200M file, with 8GB ram.

  iozone -i 0 -i 1 -i 2 -i 3 -i 4 -r 4k -s 64k -s 512m -s 1200m -b tmp.xls
  iozone -B -r 4k -s 64k -s 512m -s 1200m -b tmp.xls

The performance regression is triggered by commit 1cf6e7d83bf3(mm: task
dirty accounting fix), which makes more correct/thorough dirty
accounting.

The default 5/10 dirty ratios were picked (a) with the old dirty logic
and (b) largely at random and (c) designed to be aggressive.  In
particular, that (a) means that having fixed some of the dirty
accounting, maybe the real bug is now that it was always too aggressive,
just hidden by an accounting issue.

The enlarged 10/20 dirty ratios are just about enough to fix the regression.

[ We will have to look at how this affects the old fsync() latency issue,
  but that probably will need independent work.  - Linus ]

Cc: Nick Piggin 
Cc: Peter Zijlstra 
Reported-by: "Lin, Ming M" 
Tested-by: "Lin, Ming M" 
Signed-off-by: Wu Fengguang 
Signed-off-by: Linus Torvalds

mm: task dirty accounting fix

2009-02-18T23:37:54+00:00

YAMAMOTO-san noticed that task_dirty_inc doesn't seem to be called properly for
cases where set_page_dirty is not used to dirty a page (eg. mark_buffer_dirty).

Additionally, there is some inconsistency about when task_dirty_inc is
called.  It is used for dirty balancing, however it even gets called for
__set_page_dirty_no_writeback.

So rather than increment it in a set_page_dirty wrapper, move it down to
exactly where the dirty page accounting stats are incremented.

Cc: YAMAMOTO Takashi 
Signed-off-by: Nick Piggin 
Acked-by: Peter Zijlstra 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Fix page writeback thinko, causing Berkeley DB slowdown

2009-02-12T16:10:53+00:00

A bug was introduced into write_cache_pages cyclic writeout by commit
31a12666d8f0c22235297e1c1575f82061480029 ("mm: write_cache_pages cyclic
fix").  The intention (and comments) is that we should cycle back and
look for more dirty pages at the beginning of the file if there is no
more work to be done.

But the !done condition was dropped from the test.  This means that any
time the page writeout loop breaks (eg.  due to nr_to_write == 0), we
will set index to 0, then goto again.  This will set done_index to
index, then find done is set, so will proceed to the end of the
function.  When updating mapping->writeback_index for cyclic writeout,
we now use done_index == 0, so we're always cycling back to 0.

This seemed to be causing random mmap writes (slapadd and iozone) to
start writing more pages from the LRU and writeout would slowdown, and
caused bugzilla entry

	http://bugzilla.kernel.org/show_bug.cgi?id=12604

about Berkeley DB slowing down dramatically.

With this patch, iozone random write performance is increased nearly
5x on my system (iozone -B -r 4k -s 64k -s 512m -s 1200m on ext2).

Signed-off-by: Nick Piggin 
Reported-and-tested-by: Jan Kara 
Signed-off-by: Linus Torvalds

writeback: fix break condition

2009-02-11T22:25:37+00:00

Commit dcf6a79dda5cc2a2bec183e50d829030c0972aaa ("write-back: fix
nr_to_write counter") fixed nr_to_write counter, but didn't set the break
condition properly.

If nr_to_write == 0 after being decremented it will loop one more time
before setting done = 1 and breaking the loop.

[akpm@linux-foundation.org: coding-style fixes]
Cc: Artem Bityutskiy 
Acked-by: Nick Piggin 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds