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([2a0c:5a80:1204:1500:37e7:8150:d9df:36f]) by smtp.gmail.com with ESMTPSA id m5sm404480wrb.13.2022.02.22.08.25.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Feb 2022 08:25:41 -0800 (PST) Message-ID: <2fed0e484f223cc223c13320e62ea3648d2af227.camel@redhat.com> Subject: Re: [patch v3] mm: lru_cache_disable: replace work queue synchronization with synchronize_rcu From: Nicolas Saenz Julienne To: Marcelo Tosatti , linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org, Minchan Kim , Matthew Wilcox , Mel Gorman , Juri Lelli , Thomas Gleixner , Sebastian Andrzej Siewior , "Paul E. McKenney" Date: Tue, 22 Feb 2022 17:25:40 +0100 In-Reply-To: References: User-Agent: Evolution 3.42.4 (3.42.4-1.fc35) MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: ujxfuxm81wymitgqrqkuudmaem4tycnw X-Rspam-User: Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=ipliScPX; spf=none (imf04.hostedemail.com: domain of nsaenzju@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=nsaenzju@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 0937640010 X-HE-Tag: 1645547144-288306 Content-Transfer-Encoding: quoted-printable 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: On Tue, 2022-02-22 at 13:07 -0300, Marcelo Tosatti wrote: > On systems that run FIFO:1 applications that busy loop=20 > on isolated CPUs, executing tasks on such CPUs under > lower priority is undesired (since that will either > hang the system, or cause longer interruption to the > FIFO task due to execution of lower priority task=20 > with very small sched slices). >=20 > Commit d479960e44f27e0e52ba31b21740b703c538027c ("mm: disable LRU=20 > pagevec during the migration temporarily") relies on=20 > queueing work items on all online CPUs to ensure visibility > of lru_disable_count. >=20 > However, its possible to use synchronize_rcu which will provide the sam= e > guarantees (see comment this patch modifies on lru_cache_disable). >=20 > Fixes: >=20 > [ 1873.243925] INFO: task kworker/u160:0:9 blocked for more than 622 se= conds. > [ 1873.243927] Tainted: G I --------- --- 5.14.0-3= 1.rt21.31.el9.x86_64 #1 > [ 1873.243929] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disab= les this message. > [ 1873.243929] task:kworker/u160:0 state:D stack: 0 pid: 9 ppid:= 2 flags:0x00004000 > [ 1873.243932] Workqueue: cpuset_migrate_mm cpuset_migrate_mm_workfn > [ 1873.243936] Call Trace: > [ 1873.243938] __schedule+0x21b/0x5b0 > [ 1873.243941] schedule+0x43/0xe0 > [ 1873.243943] schedule_timeout+0x14d/0x190 > [ 1873.243946] ? resched_curr+0x20/0xe0 > [ 1873.243953] ? __prepare_to_swait+0x4b/0x70 > [ 1873.243958] wait_for_completion+0x84/0xe0 > [ 1873.243962] __flush_work.isra.0+0x146/0x200 > [ 1873.243966] ? flush_workqueue_prep_pwqs+0x130/0x130 > [ 1873.243971] __lru_add_drain_all+0x158/0x1f0 > [ 1873.243978] do_migrate_pages+0x3d/0x2d0 > [ 1873.243985] ? pick_next_task_fair+0x39/0x3b0 > [ 1873.243989] ? put_prev_task_fair+0x1e/0x30 > [ 1873.243992] ? pick_next_task+0xb30/0xbd0 > [ 1873.243995] ? __tick_nohz_task_switch+0x1e/0x70 > [ 1873.244000] ? raw_spin_rq_unlock+0x18/0x60 > [ 1873.244002] ? finish_task_switch.isra.0+0xc1/0x2d0 > [ 1873.244005] ? __switch_to+0x12f/0x510 > [ 1873.244013] cpuset_migrate_mm_workfn+0x22/0x40 > [ 1873.244016] process_one_work+0x1e0/0x410 > [ 1873.244019] worker_thread+0x50/0x3b0 > [ 1873.244022] ? process_one_work+0x410/0x410 > [ 1873.244024] kthread+0x173/0x190 > [ 1873.244027] ? set_kthread_struct+0x40/0x40 > [ 1873.244031] ret_from_fork+0x1f/0x30 >=20 > Signed-off-by: Marcelo Tosatti Reviewed-by: Nicolas Saenz Julienne Regards, --=20 Nicol=C3=A1s S=C3=A1enz