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authorEric Sandeen <sandeen@redhat.com>2010-10-27 21:30:13 -0400
committerTheodore Ts'o <tytso@mit.edu>2010-10-27 21:30:13 -0400
commit5b41d92437f1ae19b3f3ffa3b16589fd5df50ac0 (patch)
treeed7e1999a2349811e3cae0f0bdd53a93aea413d7 /include/linux/fec.h
parentbbd08344e3df8c7c1d7aa04bc0c8c9367806e12d (diff)
ext4: implement writeback livelock avoidance using page tagging
This is analogous to Jan Kara's commit, f446daaea9d4a420d16c606f755f3689dcb2d0ce mm: implement writeback livelock avoidance using page tagging but since we forked write_cache_pages, we need to reimplement it there (and in ext4_da_writepages, since range_cyclic handling was moved to there) If you start a large buffered IO to a file, and then set fsync after it, you'll find that fsync does not complete until the other IO stops. If you continue re-dirtying the file (say, putting dd with conv=notrunc in a loop), when fsync finally completes (after all IO is done), it reports via tracing that it has written many more pages than the file contains; in other words it has synced and re-synced pages in the file multiple times. This then leads to problems with our writeback_index update, since it advances it by pages written, and essentially sets writeback_index off the end of the file... With the following patch, we only sync as much as was dirty at the time of the sync. Signed-off-by: Eric Sandeen <sandeen@redhat.com> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
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