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Tue, 6 Feb 2024 09:04:59 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id zfPENjv2wWWlZwAAD6G6ig (envelope-from ); Tue, 06 Feb 2024 09:04:59 +0000 Received: by quack3.suse.cz (Postfix, from userid 1000) id 7C9CEA0809; Tue, 6 Feb 2024 10:04:59 +0100 (CET) Date: Tue, 6 Feb 2024 10:04:59 +0100 From: Jan Kara To: Jens Axboe Cc: linux-block@vger.kernel.org, linux-mm@kvack.org, Jan Kara , stable@vger.kernel.org Subject: Re: [PATCH] blk-wbt: Fix detection of dirty-throttled tasks Message-ID: <20240206090459.6a6qpb6lug3nw57g@quack3> References: <20240123175826.21452-1-jack@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240123175826.21452-1-jack@suse.cz> X-Rspamd-Queue-Id: C3AB514001D X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: zouhbz3d3ktoax5pgdxexoqgune8yhub X-HE-Tag: 1707210301-478207 X-HE-Meta: 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 9d3LIzzo reKSAtIbcb5eAV8Mnlgtc07s+edOMk+t04dk3XlAXPsuQMHwOL5AKuG6b9zadCYtl7PW6ld632MfWjt4ry0f6KOVU063azIRGjx+71iHf96EimpzGfLQfQQHS8x3USqaQZTo8ffG639S3GlEB1huuXg0gH64mu6nMnAS8OWUoDHuSeTyz6/lJn012AqPc5BA1/3/1uE/bb61QjtTyhB5lXls56QER7Y+/q3Lw9QO8aHQnNKNRQllgBga5FvAq4sGdLeAYtQOAcwtt053a+FSzoNDExeXKqMGsuGFHPjv6eXn7/73jZgEsX+xD+Ep4aUVriqK0QOl+wydAehxUiqR+f6/fgvigqy5o5MCnRmxes5drDF0= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 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 > -- Jan Kara SUSE Labs, CR