writeback, cgroup: inode_switch_wbs() shouldn't give up on wb_switch_rwsem trylock fail
As inode wb switching may make sync(2) miss some inodes, they're synchronized using wb_switch_rwsem so that no wb switching happens while sync(2) is in progress. In addition to synchronizing the actual switching, the rwsem is also used to prevent queueing new switch attempts while sync(2) is in progress. This is to avoid queueing too many instances while the rwsem is held by sync(2). Unfortunately, this is too agressive and can block wb switching for a long time if sync(2) is frequent. The goal is avoiding expolding the number of scheduled switches, not avoiding scheduling anything. Let's use wb_switch_rwsem only for synchronizing the actual switching and sync(2) and use isw_nr_in_flight instead for limiting the maximum number of scheduled switches. The limit is set to 1024 which should be more than enough while still avoiding extreme situations. Reviewed-by:Jan Kara <jack@suse.cz> Signed-off-by:
Tejun Heo <tj@kernel.org> Signed-off-by:
Jens Axboe <axboe@kernel.dk>
parent
55a694df
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