| Message ID | 20240123175826.21452-1-jack@suse.cz (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | blk-wbt: Fix detection of dirty-throttled tasks | expand |
On Tue 23-01-24 18:58:26, Jan Kara wrote: > 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: b57d74aff9ab ("writeback: track if we're sleeping on progress in balance_dirty_pages()") > Signed-off-by: Jan Kara <jack@suse.cz> Ping Jens? Honza > --- > block/blk-wbt.c | 4 ++-- > include/linux/backing-dev-defs.h | 7 +++++-- > mm/backing-dev.c | 2 +- > mm/page-writeback.c | 2 +- > 4 files changed, 9 insertions(+), 6 deletions(-) > > diff --git a/block/blk-wbt.c b/block/blk-wbt.c > index 5ba3cd574eac..0c0e270a8265 100644 > --- a/block/blk-wbt.c > +++ b/block/blk-wbt.c > @@ -163,9 +163,9 @@ static void wb_timestamp(struct rq_wb *rwb, unsigned long *var) > */ > static bool wb_recent_wait(struct rq_wb *rwb) > { > - struct bdi_writeback *wb = &rwb->rqos.disk->bdi->wb; > + struct backing_dev_info *bdi = rwb->rqos.disk->bdi; > > - return time_before(jiffies, wb->dirty_sleep + HZ); > + return time_before(jiffies, bdi->last_bdp_sleep + HZ); > } > > static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb, > diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h > index ae12696ec492..ad17739a2e72 100644 > --- a/include/linux/backing-dev-defs.h > +++ b/include/linux/backing-dev-defs.h > @@ -141,8 +141,6 @@ struct bdi_writeback { > struct delayed_work dwork; /* work item used for writeback */ > struct delayed_work bw_dwork; /* work item used for bandwidth estimate */ > > - unsigned long dirty_sleep; /* last wait */ > - > struct list_head bdi_node; /* anchored at bdi->wb_list */ > > #ifdef CONFIG_CGROUP_WRITEBACK > @@ -179,6 +177,11 @@ struct backing_dev_info { > * any dirty wbs, which is depended upon by bdi_has_dirty(). > */ > atomic_long_t tot_write_bandwidth; > + /* > + * Jiffies when last process was dirty throttled on this bdi. Used by > + * blk-wbt. > + */ > + unsigned long last_bdp_sleep; > > struct bdi_writeback wb; /* the root writeback info for this bdi */ > struct list_head wb_list; /* list of all wbs */ > diff --git a/mm/backing-dev.c b/mm/backing-dev.c > index 1e3447bccdb1..e039d05304dd 100644 > --- a/mm/backing-dev.c > +++ b/mm/backing-dev.c > @@ -436,7 +436,6 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi, > INIT_LIST_HEAD(&wb->work_list); > INIT_DELAYED_WORK(&wb->dwork, wb_workfn); > INIT_DELAYED_WORK(&wb->bw_dwork, wb_update_bandwidth_workfn); > - wb->dirty_sleep = jiffies; > > err = fprop_local_init_percpu(&wb->completions, gfp); > if (err) > @@ -921,6 +920,7 @@ int bdi_init(struct backing_dev_info *bdi) > INIT_LIST_HEAD(&bdi->bdi_list); > INIT_LIST_HEAD(&bdi->wb_list); > init_waitqueue_head(&bdi->wb_waitq); > + bdi->last_bdp_sleep = jiffies; > > return cgwb_bdi_init(bdi); > } > diff --git a/mm/page-writeback.c b/mm/page-writeback.c > index cd4e4ae77c40..cc37fa7f3364 100644 > --- a/mm/page-writeback.c > +++ b/mm/page-writeback.c > @@ -1921,7 +1921,7 @@ static int balance_dirty_pages(struct bdi_writeback *wb, > break; > } > __set_current_state(TASK_KILLABLE); > - wb->dirty_sleep = now; > + bdi->last_bdp_sleep = jiffies; > io_schedule_timeout(pause); > > current->dirty_paused_when = now + pause; > -- > 2.35.3 >
On Tue, 23 Jan 2024 18:58:26 +0100, Jan Kara wrote: > 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). > > [...] Applied, thanks! [1/1] blk-wbt: Fix detection of dirty-throttled tasks commit: f814bdda774c183b0cc15ec8f3b6e7c6f4527ba5 Best regards,
diff --git a/block/blk-wbt.c b/block/blk-wbt.c index 5ba3cd574eac..0c0e270a8265 100644 --- a/block/blk-wbt.c +++ b/block/blk-wbt.c @@ -163,9 +163,9 @@ static void wb_timestamp(struct rq_wb *rwb, unsigned long *var) */ static bool wb_recent_wait(struct rq_wb *rwb) { - struct bdi_writeback *wb = &rwb->rqos.disk->bdi->wb; + struct backing_dev_info *bdi = rwb->rqos.disk->bdi; - return time_before(jiffies, wb->dirty_sleep + HZ); + return time_before(jiffies, bdi->last_bdp_sleep + HZ); } static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb, diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h index ae12696ec492..ad17739a2e72 100644 --- a/include/linux/backing-dev-defs.h +++ b/include/linux/backing-dev-defs.h @@ -141,8 +141,6 @@ struct bdi_writeback { struct delayed_work dwork; /* work item used for writeback */ struct delayed_work bw_dwork; /* work item used for bandwidth estimate */ - unsigned long dirty_sleep; /* last wait */ - struct list_head bdi_node; /* anchored at bdi->wb_list */ #ifdef CONFIG_CGROUP_WRITEBACK @@ -179,6 +177,11 @@ struct backing_dev_info { * any dirty wbs, which is depended upon by bdi_has_dirty(). */ atomic_long_t tot_write_bandwidth; + /* + * Jiffies when last process was dirty throttled on this bdi. Used by + * blk-wbt. + */ + unsigned long last_bdp_sleep; struct bdi_writeback wb; /* the root writeback info for this bdi */ struct list_head wb_list; /* list of all wbs */ diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 1e3447bccdb1..e039d05304dd 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -436,7 +436,6 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi, INIT_LIST_HEAD(&wb->work_list); INIT_DELAYED_WORK(&wb->dwork, wb_workfn); INIT_DELAYED_WORK(&wb->bw_dwork, wb_update_bandwidth_workfn); - wb->dirty_sleep = jiffies; err = fprop_local_init_percpu(&wb->completions, gfp); if (err) @@ -921,6 +920,7 @@ int bdi_init(struct backing_dev_info *bdi) INIT_LIST_HEAD(&bdi->bdi_list); INIT_LIST_HEAD(&bdi->wb_list); init_waitqueue_head(&bdi->wb_waitq); + bdi->last_bdp_sleep = jiffies; return cgwb_bdi_init(bdi); } diff --git a/mm/page-writeback.c b/mm/page-writeback.c index cd4e4ae77c40..cc37fa7f3364 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -1921,7 +1921,7 @@ static int balance_dirty_pages(struct bdi_writeback *wb, break; } __set_current_state(TASK_KILLABLE); - wb->dirty_sleep = now; + bdi->last_bdp_sleep = jiffies; io_schedule_timeout(pause); current->dirty_paused_when = now + pause;
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: b57d74aff9ab ("writeback: track if we're sleeping on progress in balance_dirty_pages()") Signed-off-by: Jan Kara <jack@suse.cz> --- block/blk-wbt.c | 4 ++-- include/linux/backing-dev-defs.h | 7 +++++-- mm/backing-dev.c | 2 +- mm/page-writeback.c | 2 +- 4 files changed, 9 insertions(+), 6 deletions(-)