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blk-wbt: Fix detection of dirty-throttled tasks
The detection of dirty-throttled tasks in blk-wbt has been subtly broken
since its beginning in 2016. Namely if we are doing cgroup writeback and
the throttled task is not in the root cgroup, balance_dirty_pages() will
set dirty_sleep for the non-root bdi_writeback structure. However
blk-wbt checks dirty_sleep only in the root cgroup bdi_writeback
structure. Thus detection of recently throttled tasks is not working in
this case (we noticed this when we switched to cgroup v2 and suddently
writeback was slow).
Since blk-wbt has no easy way to get to proper bdi_writeback and
furthermore its intention has always been to work on the whole device
rather than on individual cgroups, just move the dirty_sleep timestamp
from bdi_writeback to backing_dev_info. That fixes the checking for
recently throttled task and saves memory for everybody as a bonus.
CC: stable@vger.kernel.org
Fixes: b57d74aff9
("writeback: track if we're sleeping on progress in balance_dirty_pages()")
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20240123175826.21452-1-jack@suse.cz
[axboe: fixup indentation errors]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
parent
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@ -163,9 +163,9 @@ static void wb_timestamp(struct rq_wb *rwb, unsigned long *var)
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*/
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static bool wb_recent_wait(struct rq_wb *rwb)
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{
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struct bdi_writeback *wb = &rwb->rqos.disk->bdi->wb;
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struct backing_dev_info *bdi = rwb->rqos.disk->bdi;
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return time_before(jiffies, wb->dirty_sleep + HZ);
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return time_before(jiffies, bdi->last_bdp_sleep + HZ);
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}
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static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb,
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@ -141,8 +141,6 @@ struct bdi_writeback {
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struct delayed_work dwork; /* work item used for writeback */
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struct delayed_work bw_dwork; /* work item used for bandwidth estimate */
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unsigned long dirty_sleep; /* last wait */
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struct list_head bdi_node; /* anchored at bdi->wb_list */
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#ifdef CONFIG_CGROUP_WRITEBACK
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@ -179,6 +177,11 @@ struct backing_dev_info {
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* any dirty wbs, which is depended upon by bdi_has_dirty().
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*/
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atomic_long_t tot_write_bandwidth;
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/*
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* Jiffies when last process was dirty throttled on this bdi. Used by
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* blk-wbt.
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*/
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unsigned long last_bdp_sleep;
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struct bdi_writeback wb; /* the root writeback info for this bdi */
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struct list_head wb_list; /* list of all wbs */
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@ -436,7 +436,6 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,
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INIT_LIST_HEAD(&wb->work_list);
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INIT_DELAYED_WORK(&wb->dwork, wb_workfn);
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INIT_DELAYED_WORK(&wb->bw_dwork, wb_update_bandwidth_workfn);
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wb->dirty_sleep = jiffies;
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err = fprop_local_init_percpu(&wb->completions, gfp);
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if (err)
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@ -921,6 +920,7 @@ int bdi_init(struct backing_dev_info *bdi)
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INIT_LIST_HEAD(&bdi->bdi_list);
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INIT_LIST_HEAD(&bdi->wb_list);
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init_waitqueue_head(&bdi->wb_waitq);
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bdi->last_bdp_sleep = jiffies;
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return cgwb_bdi_init(bdi);
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}
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@ -1921,7 +1921,7 @@ pause:
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break;
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}
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__set_current_state(TASK_KILLABLE);
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wb->dirty_sleep = now;
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bdi->last_bdp_sleep = jiffies;
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io_schedule_timeout(pause);
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current->dirty_paused_when = now + pause;
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