]> git.proxmox.com Git - mirror_ubuntu-kernels.git/commit
mm/filemap.c: don't initiate writeback if mapping has no dirty pages
authorKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Mon, 23 Sep 2019 22:34:45 +0000 (15:34 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Tue, 24 Sep 2019 22:54:08 +0000 (15:54 -0700)
commitc3aab9a0bd91b696a852169479b7db1ece6cbf8c
treed23029d8d038a4485f8f71f5c62f0543b84f74e6
parent8974558f49a6a41b4a74db672e13bca616eff6d8
mm/filemap.c: don't initiate writeback if mapping has no dirty pages

Functions like filemap_write_and_wait_range() should do nothing if inode
has no dirty pages or pages currently under writeback.  But they anyway
construct struct writeback_control and this does some atomic operations if
CONFIG_CGROUP_WRITEBACK=y - on fast path it locks inode->i_lock and
updates state of writeback ownership, on slow path might be more work.
Current this path is safely avoided only when inode mapping has no pages.

For example generic_file_read_iter() calls filemap_write_and_wait_range()
at each O_DIRECT read - pretty hot path.

This patch skips starting new writeback if mapping has no dirty tags set.
If writeback is already in progress filemap_write_and_wait_range() will
wait for it.

Link: http://lkml.kernel.org/r/156378816804.1087.8607636317907921438.stgit@buzz
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/filemap.c