From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793967691; b=r/vtSutJvzArlG+53h420b8RvqtIwHpjbaCoEeU9lav7ZaQp5UFSfxrePj0Gzjb+JgF7 QSthgdeDwGa2eMF2n40nPwEiNuueWd13AtWa2oxiDvKQB07oRbjiM6WqXq26a/cmvtvnS EVB4t2hGPvdZZ08cXIsYBalY44OGXwkZCM3Yj8htF33XYNiP1T3b2nV3hWJRMoELRHNhU A6/ew3Sjrv4febOqlrJ7y2z60G1Yp7TnI3md0Lrji98ceE5vp6OZDR79OpMdpGJeBF//A eDozJYMV74cPLExhTFKuBrOc0q4htVHE/IrG9IruC0pQsJT8UENQOM+FGOC4GTLGR+w== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793967691; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=cRzTH+yd4d8od9LM7sI2UHx2nrHb7DkZirOlIhvtcmU=; b=cOGRsYFWj5AkxbiNgGVq+ofijt2Pcmc7lDWFkc3zZlXR2tQ65PQIWzFVJvKVgEBviajJ cjt+aT0ImWznCMEyoMWATUdtbAFawF0hwuIqMoVFjHhxvhiGOEW0+UrD9gXC2yk44SUys HeUYkAt61RhkBckdRjskw5xNorCau8n9goswhkWGbqoe6JkpkSJjGZ6ME4RLY45cvP93X Pa2jNAbVV6HSZPbGQDnb+PuAVV2QBMI7AnN9Ohk5fGKQ+6ZXWMsoI7Wwe/OB78lKttVey 9FIFmvZpvOnqDRPRxJa9azRaEqJHIbzFg5V7xMbYkueHWTtGQGCyjZl05V1b/2LAf2A== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=GZILsJYw; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 75B4B606A326; Fri, 6 Nov 2026 12:21:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=GZILsJYw Received: by smtp.kernel.org (Postfix) with ESMTPSA id 8F25F1F0089F; Fri, 6 Nov 2026 12:21:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793967691; bh=cRzTH+yd4d8od9LM7sI2UHx2nrHb7DkZirOlIhvtcmU=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=GZILsJYwu5BayQcmz0opObBE0Ra84AH2emZVoDsYwET5lsnXq/90QfHCKSiuVcyng QK6GS6TxvENK+/sND0HJk/pISIlyglRaJyq+yYhObAQDtBYNHdEpVa63IlVAN5jN2n Bl71ZLc1hzVRPjVqVBic13CoXv5zTenBbEqK2e4ETjWnl2nEyM+OP3mMgP/jgfMMhI gkeW+EK9keSGXtJBvkIbdh35aMPfca1IHC/jAU7w9xnDnPoyviV3mUPcSBB7hkElxv wte2pRHKe9ddWnUtU/1XJDkCxQk3YddRhQ4Og723Jd8cfqg3VuPHeQIezaf2h/RZEN Fe1/F8bvxLhzA== Date: Fri, 6 Nov 2026 12:21:28 +0000 From: Harry Yoo To: Uladzislau Rezki Cc: Zhan Xusheng , vbabka@kernel.org, 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-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, Nov 06, 2026 at 10:35:13AM +0100, Uladzislau Rezki wrote: > 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? You mean clamp to [1:100,000] milliseconds 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? IMO in general we should keep existing behaviour unless we could demonstrate setting a delay < 1ms is fundamentally flawed? -- Cheers, Harry / Hyeonggon