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>
3 files changed
