From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8BF6EC433F5 for ; Mon, 21 Feb 2022 14:46:34 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id C2D5A8D0002; Mon, 21 Feb 2022 09:46:33 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id BDC5D8D0001; Mon, 21 Feb 2022 09:46:33 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id ACB2F8D0002; Mon, 21 Feb 2022 09:46:33 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0181.hostedemail.com [216.40.44.181]) by kanga.kvack.org (Postfix) with ESMTP id 9CD708D0001 for ; Mon, 21 Feb 2022 09:46:33 -0500 (EST) Received: from smtpin13.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 4E3E48249980 for ; Mon, 21 Feb 2022 14:46:33 +0000 (UTC) X-FDA: 79167063066.13.E3B5791 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by imf05.hostedemail.com (Postfix) with ESMTP id B31A5100009 for ; Mon, 21 Feb 2022 14:46:32 +0000 (UTC) Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 9E74621127; Mon, 21 Feb 2022 14:46:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1645454791; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=EqsD0+PUucg5iQZfEeVVmjRSWohazjOc9cWwEfg7gWQ=; b=S9RSPoFRigrL5qMv/KMVZC7pUGpUkd/8yaw0GTN00pBHVYNtVUVkqFaUKo5sOpLFxhaNEP C3MbcBsSyVJnzwDSA0jGAX/qFbmIl7vZ4hdBnEY4g+Jvez705ER6wV3LCJSOJurw8Enq1u b5Rasq4exl90T33lXZSWWnyCQbWx40w= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 6EB88A3B83; Mon, 21 Feb 2022 14:46:31 +0000 (UTC) Date: Mon, 21 Feb 2022 15:46:30 +0100 From: Michal Hocko To: Sebastian Andrzej Siewior Cc: cgroups@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Johannes Weiner , Michal =?iso-8859-1?Q?Koutn=FD?= , Peter Zijlstra , Thomas Gleixner , Vladimir Davydov , Waiman Long , kernel test robot Subject: Re: [PATCH v3 5/5] mm/memcg: Protect memcg_stock with a local_lock_t Message-ID: References: <20220217094802.3644569-1-bigeasy@linutronix.de> <20220217094802.3644569-6-bigeasy@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220217094802.3644569-6-bigeasy@linutronix.de> X-Stat-Signature: kt6swbjmzargnzyhnu134joatqewzun7 X-Rspam-User: Authentication-Results: imf05.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=S9RSPoFR; spf=pass (imf05.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.28 as permitted sender) smtp.mailfrom=mhocko@suse.com; dmarc=pass (policy=quarantine) header.from=suse.com X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: B31A5100009 X-HE-Tag: 1645454792-311254 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 Thu 17-02-22 10:48:02, Sebastian Andrzej Siewior wrote: [...] > @@ -2266,7 +2273,6 @@ static void drain_all_stock(struct mem_cgroup *root_memcg) > * as well as workers from this path always operate on the local > * per-cpu data. CPU up doesn't touch memcg_stock at all. > */ > - curcpu = get_cpu(); Could you make this a separate patch? > for_each_online_cpu(cpu) { > struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu); > struct mem_cgroup *memcg; > @@ -2282,14 +2288,9 @@ static void drain_all_stock(struct mem_cgroup *root_memcg) > rcu_read_unlock(); > > if (flush && > - !test_and_set_bit(FLUSHING_CACHED_CHARGE, &stock->flags)) { > - if (cpu == curcpu) > - drain_local_stock(&stock->work); > - else > - schedule_work_on(cpu, &stock->work); > - } > + !test_and_set_bit(FLUSHING_CACHED_CHARGE, &stock->flags)) > + schedule_work_on(cpu, &stock->work); Maybe I am missing but on !PREEMPT kernels there is nothing really guaranteeing that the worker runs so there should be cond_resched after the mutex is unlocked. I do not think we want to rely on callers to be aware of this subtlety. An alternative would be to split out __drain_local_stock which doesn't do local_lock. -- Michal Hocko SUSE Labs