On Fri, Apr 21, 2023 at 10:40 AM Yosry Ahmed <yosryahmed@xxxxxxxxxx> wrote: > > wb_over_bg_thresh() calls mem_cgroup_wb_stats() which invokes an rstat > flush, which can be expensive on large systems. Currently, > wb_writeback() calls wb_over_bg_thresh() within a lock section, so we > have to do the rstat flush atomically. On systems with a lot of > cpus and/or cgroups, this can cause us to disable irqs for a long time, > potentially causing problems. > > Move the call to wb_over_bg_thresh() outside the lock section in > preparation to make the rstat flush in mem_cgroup_wb_stats() non-atomic. > The list_empty(&wb->work_list) check should be okay outside the lock > section of wb->list_lock as it is protected by a separate lock > (wb->work_lock), and wb_over_bg_thresh() doesn't seem like it is > modifying any of wb->b_* lists the wb->list_lock is protecting. > Also, the loop seems to be already releasing and reacquring the > lock, so this refactoring looks safe. > > Signed-off-by: Yosry Ahmed <yosryahmed@xxxxxxxxxx> > Reviewed-by: Michal Koutný <mkoutny@xxxxxxxx> > Reviewed-by: Jan Kara <jack@xxxxxxx> Acked-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
