Messages in this thread | | | Date | Thu, 29 Apr 2010 14:39:31 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 3/4] writeback: pay attention to wbc->nr_to_write in write_cache_pages |
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On Tue, 20 Apr 2010 12:41:53 +1000 Dave Chinner <david@fromorbit.com> wrote:
> If a filesystem writes more than one page in ->writepage, write_cache_pages > fails to notice this and continues to attempt writeback when wbc->nr_to_write > has gone negative - this trace was captured from XFS: > > > wbc_writeback_start: towrt=1024 > wbc_writepage: towrt=1024 > wbc_writepage: towrt=0 > wbc_writepage: towrt=-1 > wbc_writepage: towrt=-5 > wbc_writepage: towrt=-21 > wbc_writepage: towrt=-85 >
Bug.
AFAIT it's a regression introduced by
: commit 17bc6c30cf6bfffd816bdc53682dd46fc34a2cf4 : Author: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com> : AuthorDate: Thu Oct 16 10:09:17 2008 -0400 : Commit: Theodore Ts'o <tytso@mit.edu> : CommitDate: Thu Oct 16 10:09:17 2008 -0400 : : vfs: Add no_nrwrite_index_update writeback control flag
I suggest that what you do here is remove the local `nr_to_write' from write_cache_pages() and go back to directly using wbc->nr_to_write within the loop.
And thus we restore the convention that if the fs writes back more than a single page, it subtracts (nr_written - 1) from wbc->nr_to_write.
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