The patch titled
Subject: mm/filemap.c: don't initiate writeback if mapping has no dirty pages
has been added to the -mm tree. Its filename is
mm-filemap-dont-initiate-writeback-if-mapping-has-no-dirty-pages.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-filemap-dont-initiate-writeback-if-mapping-has-no-dirty-pages.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-filemap-dont-initiate-writeback-if-mapping-has-no-dirty-pages.patch
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------------------------------------------------------
From: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Subject: 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@xxxxxxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/mm/filemap.c~mm-filemap-dont-initiate-writeback-if-mapping-has-no-dirty-pages
+++ a/mm/filemap.c
@@ -408,7 +408,8 @@ int __filemap_fdatawrite_range(struct ad
.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);
_
Patches currently in -mm which might be from khlebnikov@xxxxxxxxxxxxxx are
mm-filemap-dont-initiate-writeback-if-mapping-has-no-dirty-pages.patch
mm-filemap-rewrite-mapping_needs_writeback-in-less-fancy-manner.patch
