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Fri, 06 Nov 2026 01:35:15 -0800 (PST) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Fri, 6 Nov 2026 10:35:13 +0100 To: Zhan Xusheng Cc: vbabka@kernel.org, harry@kernel.org, urezki@gmail.com, paulmck@kernel.org, qiang.zhang@linux.dev, akpm@linux-foundation.org, hao.li@linux.dev, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, rcu@vger.kernel.org, linux-kernel@vger.kernel.org, zhanxusheng@xiaomi.com Subject: Re: [PATCH 2/2] mm/slab: don't queue the page cache work under krcp->lock Message-ID: References: <20261028134647.3176080-1-zhanxusheng1024@gmail.com> <20261028134647.3176080-2-zhanxusheng1024@gmail.com> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261028134647.3176080-2-zhanxusheng1024@gmail.com> X-Stat-Signature: fum6ndbb3bhicr17s7bxxrdjwti4pc8g X-Rspamd-Queue-Id: 959C7A0005 X-Rspam-User: X-Rspamd-Server: rspam08 X-Spam-Status: No, score=-12.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=ham autolearn_force=no version=4.0.1 X-HE-Tag: 1793957717-820121 X-HE-Meta: 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 XbHfSEBh 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Wed, Oct 28, 2026 at 09:46:47PM +0800, Zhan Xusheng wrote: > From: Zhan Xusheng > > run_page_cache_worker() runs under krcp->lock, from kvfree_call_rcu() > callers that may hold more, such as set_cpus_allowed_force() under > pi_lock, so it kicks the refill work from an hrtimer. Under memory > pressure it instead queues the work with a delay of > rcutree.rcu_delay_page_cache_fill_msec, which may be 0, and a zero delay > queues it at once, taking pool->lock under krcp->lock. > > With the delay set to 0, calling kvfree_rcu() on vmalloc memory under > pi_lock after a drop_caches makes lockdep report: > > Chain exists of: > &pool->lock --> &p->pi_lock --> krc.lock > > Use the hrtimer when the delay is 0. > > Fixes: d0bfa8b3c411 ("kvfree_rcu: Release a page cache under memory pressure") > Signed-off-by: Zhan Xusheng > --- > mm/slab_common.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/mm/slab_common.c b/mm/slab_common.c > index 3729aa7a6156..ef5ff0a20249 100644 > --- a/mm/slab_common.c > +++ b/mm/slab_common.c > @@ -1987,7 +1987,13 @@ run_page_cache_worker(struct kfree_rcu_cpu *krcp) > > if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING && > !atomic_xchg(&krcp->work_in_progress, 1)) { > - if (atomic_read(&krcp->backoff_page_cache_fill)) { > + /* > + * A zero delay would queue the work right here, under > + * krcp->lock and possibly the caller's pi_lock, so let the > + * hrtimer do it. > + */ > + if (atomic_read(&krcp->backoff_page_cache_fill) && > + rcu_delay_page_cache_fill_msec) { > queue_delayed_work(rcu_reclaim_wq, > &krcp->page_cache_work, > msecs_to_jiffies(rcu_delay_page_cache_fill_msec)); > -- > 2.43.0 > > Can we just clamp this to 1 - 100 seconds interval? diff --git a/mm/slab_common.c b/mm/slab_common.c index 7223a7596dab..2c9236236ac9 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -2249,12 +2249,12 @@ void __init kvfree_rcu_init(void) WQ_UNBOUND | WQ_MEM_RECLAIM, 0); WARN_ON(!rcu_reclaim_wq); - /* Clamp it to [0:100] seconds interval. */ - if (rcu_delay_page_cache_fill_msec < 0 || + /* Clamp it to [1:100] seconds interval. */ + if (rcu_delay_page_cache_fill_msec <= 0 || rcu_delay_page_cache_fill_msec > 100 * MSEC_PER_SEC) { rcu_delay_page_cache_fill_msec = - clamp(rcu_delay_page_cache_fill_msec, 0, + clamp(rcu_delay_page_cache_fill_msec, 1, (int) (100 * MSEC_PER_SEC)); pr_info("Adjusting rcutree.rcu_delay_page_cache_fill_msec to %d ms.\n", so we forbid zero as value to use? -- Uladzislau Rezki