On Sat 31-07-10 11:33:22, Mel Gorman wrote:

On Fri, Jul 30, 2010 at 03:06:01PM -0700, Andrew Morton wrote:

quoted

Sigh.  We have sooo many problems with writeback and latency.  Read
https://bugzilla.kernel.org/show_bug.cgi?id=12309 and weep.

You aren't joking.

quoted

Everyone's
running away from the issue and here we are adding code to solve some
alleged stack-overflow problem which seems to be largely a non-problem,
by making changes which may worsen our real problems.

As it is, filesystems are beginnning to ignore writeback from direct
reclaim - such as xfs and btrfs. I'm lead to believe that ext3
effectively ignores writeback from direct reclaim although I don't have
access to code at the moment to double check (am on the road). So either
way, we are going to be facing this problem so the VM might as well be
aware of it :/

  Umm, ext3 should be handling direct reclaim just fine. ext4 does however
ignore it when a page does not have block already allocated (which is a
common case with delayed allocation).

								Honza
-- 
Jan Kara [off-list ref]
SUSE Labs, CR

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