tree be98d2e503cc6caa3700b0a281847af020731059
parent 2cd68615b12a66fe24e503b7b35d4ca43833f77d
author Tejun Heo <tj@kernel.org> 1420575271 -0500
committer Tejun Heo <tj@kernel.org> 1420575271 -0500

writeback: make write_cache_pages() cgroup writeback aware

write_cache_pages() is used to implement generic do_writepages().  Up
until now, the function targeted all dirty pages; however, for cgroup
writeback, it needs to be more restrained.  As writeback for each wb
cgroup (bdi_writeback) will be executed separately, do_writepages()
needs to write out only the pages dirtied against the wb being
serviced.

This patch introduces wbc_skip_page() which is used by
write_cache_pages() to determine whether a page should be skipped
because it is dirtied against a different wb.  wbc->iwbl_mismatch is
also added to keep track of whether pages were skipped, which will be
used later.

Filesystems which don't use write_cache_pages() for its
address_space_operation->writepages() should update its ->writepages()
to use wbc_skip_page() directly to support cgroup writeback.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>