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authorKonstantin Khlebnikov <khlebnikov@yandex-team.ru>2019-09-24 01:34:45 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2019-09-25 01:54:08 +0300
commitc3aab9a0bd91b696a852169479b7db1ece6cbf8c (patch)
treed23029d8d038a4485f8f71f5c62f0543b84f74e6
parent8974558f49a6a41b4a74db672e13bca616eff6d8 (diff)
downloadlinux-c3aab9a0bd91b696a852169479b7db1ece6cbf8c.tar.xz
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>
-rw-r--r--mm/filemap.c3
1 files changed, 2 insertions, 1 deletions
diff --git a/mm/filemap.c b/mm/filemap.c
index 5f30aedd7363..82f3b9a3a940 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -408,7 +408,8 @@ int __filemap_fdatawrite_range(struct address_space *mapping, loff_t start,
.range_end = end,
};
- if (!mapping_cap_writeback_dirty(mapping))
+ if (!mapping_cap_writeback_dirty(mapping) ||
+ !mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
return 0;
wbc_attach_fdatawrite_inode(&wbc, mapping->host);