writeback: make __filemap_fdatawrite_range() croup writeback aware
__filemap_fdatawrite_range() and its friends are used, among other
things, to implement fsync and coordinate buffered and direct IOs.
The function directly invokes do_writepages() bypassing the usual fs
writeback mechanism and thus currently doesn't respect cgroup
writeback.
This patch adds wb_writeback_work->mapping[_range_{start|end}] which
are used to instruct wb_writeback_work item to execute do_writepages()
on a single mapping. A new function cgwb_do_writepages() is added
which splits do_writepages() to all dirtying wb's (bdi_writeback's)
using this new work type. __filemap_fdatawrite_range() is updated to
use cgwb_do_writepages() instead of do_writepages().
cgwb_do_writepages() first tries direct do_writepages() on the current
blkcg as it's likely that the calling cgroup is trying to flush pages
that it dirtied. If that doesn't write out all pages, it issues
single mappign work items to all wb's with dirty pages on the target
mapping. It currently doesn't distribute wbc->nr_to_write according
to the bandwidth proportion of each wb. If this ever becomes
necessary, implementing it shouldn't be too difficult.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
3 files changed
