From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=209.85.218.53 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793957718; b=O2KpTRRUYQAeUebK8ApUdJhFlw9dpGCq7TLRXwEaq63y/cbgbh25CN9A2zqprNmuNoX6 FQj1ddawdtQbIZ3fBz32VVJ0RfAiHrDZV1O3+To5j1CfLTeQWDZszIgVYHaMDd0AEjbD3 hkiWvWtrXXUPAsVMxGs9tSqmfsxpsNF2z3Si/wBZT5JZD0hWCdILJBzeH44wgFpbu1r3r FidB3oceaUI5Vs8X6/tg75uHn+mpv6+R7E9oTzYsXK4o7HqxmUjopUARnTJYvsVwDxsF3 db4KdaC0A9RwCcmiHmJMQ2ZZzvkpI+I+Lhsv41X6wVOACyprli6wGKeqRK+wKU5i+5A== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793957718; h=DMARC-Filter:Received:DKIM-Signature:X-Google-DKIM-Signature: X-Forwarded-Encrypted:X-Gm-Message-State:X-Gm-Gg:X-Received:Received: From:X-Google-Original-From:Date:To:Cc:Subject:Message-ID:References: MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=e+beHwPVnOrx0jzUBZNVM2/8fCDJRY0y3tTo+TmZt0s=; b=qsqhmM4z4ETjzVrlZjluAArLeMnleD+IevC5I6Zqd4YMU56IOjlGvbpOaDjCicO86loV QUS33aSrat9qDZ3tLgtqLM6xfgFBtSX+plmGaiUCR80PAeS+J92fcdQIN2LSstWDIVw/A 8Z3YZnHarVJf+DVryEmOYPZbNExGeHloqefVAuHqU3nVVS9qm7Mf6VSCRsb43qh0flIia 37vXRgZSNcHznCnFSTCy+2IRygMPJir4/QM19LBs3GuddiV9jhBvc3FZCir4jmDdJoDwc RnT9DHNRHr6D5sxogusZQziPSNbieGnIUaRLsH5OGoN3l3hKtNZH/pQ4KySr7iV9tgw== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=eGxrb6hE; arc=none smtp.remote-ip=209.85.218.53 Received: from mail-ej1-f53.google.com (mail-ej1-f53.google.com [209.85.218.53]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B329E606D829 for ; Fri, 6 Nov 2026 09:35:17 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org B329E606D829 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=gmail.com header.i=@gmail.com header.a=rsa-sha256 header.s=20260707 header.b=eGxrb6hE Received: by mail-ej1-f53.google.com with SMTP id a640c23a62f3a-c414e5d282eso57788166b.1 for ; Fri, 06 Nov 2026 01:35:17 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20260707; t=1793957716; x=1794562516; darn=vger.kernel.org; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:date:from:from:to:cc:subject :date:message-id:reply-to:content-type; bh=e+beHwPVnOrx0jzUBZNVM2/8fCDJRY0y3tTo+TmZt0s=; b=eGxrb6hEW88atCdNy0tSfzxZ2DmYRRZnEzfrKDE47vNJ1C8+MVMJHFLz8nyZZFYPc2 YbkEWrk+st5rKjhADm4H2dF6en2AuSRGEw43DnZ3g/jxxuNxor8FZX8SKpiBeHyAeYlK yEjky+hYTOzLxY3ClZRQt3hW/8uP6+jaK8fVbrZYld0qnS4Q2e2ZkFkMvtdRr7KRh1Qp Hu3mn3A8WPM+z35IPd2alklUeFgQAoLjbau1IMu9wNXYJ45dVpIAEGfRYqpTh/ZeNaG+ 5ggTcLMo1ZvB2zuxqPhwWl4bHLEfloC8ciV5WQB+znFUOcWWB32Cw7g+71ZjZhUIwWg6 UN3w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1793957716; x=1794562516; h=in-reply-to:content-disposition:content-type:mime-version :references:message-id:subject:cc:to:date:from:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=e+beHwPVnOrx0jzUBZNVM2/8fCDJRY0y3tTo+TmZt0s=; b=rNlI4zWhayJZ0t3gh3NGqrKMvujFkB6msvQUjlG9ZM+XtpTz1k+zGf1mFVm8+aCXO6 xOjEg/aB/xYvSmHEYfrw5jEfAiIEz8N/KgExfvH8jX9P2t7uuyoun/RNF3Skt/PG3ij6 a42nB9aBlTUDODruCnnpgQxU+RN7KQ6pRfR0VKuHAbtvnUArbw0Jr9ksUn4drPyG+Cqi giedxfOBCg8TwUKPtibSYI4XGa+XQB0K1xHbegjeg1e1ZHPSLKMnFin8E+24kDHAqcgp n0DS1NWR2aycAxUJI3i/wolXLww0sfflwmnGvOMcf3L4/lx3bcLhwD5YKJgH8+fxhfCA RgAQ== X-Forwarded-Encrypted: i=1; AKwUvBw+eeINHKgp7CriWQwHnoz9bhFhe/g9iE1OTb7du6+Lnq8G37dFblCxK7nq7xtJbgkeqYaY9qWzeBEderE=@vger.kernel.org X-Gm-Message-State: APuU4Z/mKRrCsdbjfTVOKrf4euf+5iaUp9I5p8vmEpiWRoCkaMjCISuy LwI6dO2b+4KAQkjKbhr0vaciNTCLSW3f3Nu5qKndh3RiAdQx+K7eE8zt X-Gm-Gg: AYBFou2V7ETin6cnvyitxtZWAnvqVzCDblwnVAn4pbdXf8bDyuvruq1xNrASoqzp4wi V8NQ80Hjzbo+Km3NxK7S4FsU8dGgmqfY38o8nh/ScUNtK3pk99pAQQfhyLqRou7BJMTq71sjE7O i/XYLjlUmbtvZ3vyW5RED/WmcMnejCdF2aVGWlMHCMAKtC1s10jw6LO/lsAJ/Z+tirng9N+hzEE 8GM39XsxqpfZtkJVTNaeXKM3OxYDtop/tMBDXE7Le6Wb9W/BnXj02tifvlZZlH2j/csfF9Q6tbG +0q+WP7PsPO2/kEQ8qSoHimxpNS5ffZ3f4EleMLm+ZZfhExYUZkJwKxKdNBvl5h3PUFtI3FdCBI E5qx44X5fgabteeRaZc8fIup4XS2YT4SNwJNG/TYTTNQm2h04B0SXFm0TU8HVXvn0Ij8g22f0x6 mxaeuntqgdRh2cPln8lyp0h2khrseY7TlVwcYEDTpZOrgnOgwGbENMleE5NEAWD9C+9NmHGWFzb jclcAyP3zMbEJ5XiSfbZa0t8P7mvb3bp+3ZYJsgEDKog3o/pBNfGcra/UPc/bp8GX5c X-Received: by 2002:a17:907:a892:b0:c3f:153a:8663 with SMTP id a640c23a62f3a-c4d34bdd8camr155235166b.23.1793957715953; Fri, 06 Nov 2026 01:35:15 -0800 (PST) Received: from milan ([2001:9b1:d5a0:a500::24b]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-c4d35670169sm65381266b.42.2026.11.06.01.35.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); 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-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: <20261028134647.3176080-2-zhanxusheng1024@gmail.com> 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