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 28659C25B50 for ; Mon, 23 Jan 2023 09:59:21 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 82A1A6B0072; Mon, 23 Jan 2023 04:59:20 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 7D8406B0073; Mon, 23 Jan 2023 04:59:20 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 6A03E6B0074; Mon, 23 Jan 2023 04:59:20 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id 5C30C6B0072 for ; Mon, 23 Jan 2023 04:59:20 -0500 (EST) Received: from smtpin15.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 8A248AAA7B for ; Mon, 23 Jan 2023 09:59:19 +0000 (UTC) X-FDA: 80385616038.15.12B4709 Received: from smtp-out1.suse.de (smtp-out1.suse.de [195.135.220.28]) by imf10.hostedemail.com (Postfix) with ESMTP id 9797BC0005 for ; Mon, 23 Jan 2023 09:59:17 +0000 (UTC) Authentication-Results: imf10.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=j6fAAr3M; spf=pass (imf10.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 ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1674467957; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=RPUgUWLYFyzDTJWxeUhyD8C/Rk27j6KTINncM5ul7B8=; b=ZOZ7AwFEi5yqImWPFeCQ8HIPaYzmRlZ+dZHuPKy82TpP7wdCY+3u7VqTmNRlesii9wv/XK PMVy0veNeIKcx9cvWxcS3xgPGn6FAiZnqNVZo4p+g1OHPvFGzKrdyxLHQEMmWKVKl+xDy5 piG684fyelRkhfsnxdy0ilpEygfI5/Q= ARC-Authentication-Results: i=1; imf10.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=j6fAAr3M; spf=pass (imf10.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 ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1674467957; a=rsa-sha256; cv=none; b=P4mQAHpT7EMd7FNoKboXyGu8yy1MQbjirTEKMlnP9ojQJzIC49Vxg/DzXWCOkZ5IdX2aTd ZYjSsUc77+BQFEmLTPIyDwxoH466g1XJrKT8Fe5tpHL95gfieigtckqhd3cAm7ZGHfNAlz 9RHZzW/D3r4NkvLdBQA8lBGVy1N16FA= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by smtp-out1.suse.de (Postfix) with ESMTPS id BBD49220BE; Mon, 23 Jan 2023 09:59:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1674467955; 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=RPUgUWLYFyzDTJWxeUhyD8C/Rk27j6KTINncM5ul7B8=; b=j6fAAr3MXQF3Ag61iljXv6JHlPeeziIdplAnwUZmokoMW/gVtX233B/+80pEJK01C5GlkJ EPzsRhAPlyG+3HBY8AjSiPzwO3AjfsTiqVjoPnDjgoPLncHoHzPgtbHjrCu+oUdXF8LEnw 3tP7uTNe6KPkoGsvMwkZiOP+TEPQb3k= Received: from imap2.suse-dmz.suse.de (imap2.suse-dmz.suse.de [192.168.254.74]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (P-521) server-digest SHA512) (No client certificate requested) by imap2.suse-dmz.suse.de (Postfix) with ESMTPS id 7FFFC134F5; Mon, 23 Jan 2023 09:59:15 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id 09ywHnNazmOiCwAAMHmgww (envelope-from ); Mon, 23 Jan 2023 09:59:15 +0000 Date: Mon, 23 Jan 2023 10:59:14 +0100 From: Michal Hocko To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, michel@lespinasse.org, jglisse@google.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org, ldufour@linux.ibm.com, laurent.dufour@fr.ibm.com, paulmck@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, jannh@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, gurua@google.com, arjunroy@google.com, soheil@google.com, hughlynch@google.com, leewalsh@google.com, posk@google.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Subject: Re: [PATCH 39/41] kernel/fork: throttle call_rcu() calls in vm_area_free Message-ID: References: <20230109205336.3665937-1-surenb@google.com> <20230109205336.3665937-40-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: 9797BC0005 X-Stat-Signature: 1kg7pxunnx9jyhj3xztmc1rmsuimb3yh X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1674467957-470937 X-HE-Meta: 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 NLVj6b9U TYdlHomborhYFDa9/WdSO7MC5iUaFCslbVOnZO8bnryPCZfgpdazzosezKGMGBg4KL6sNemyQq50HMNifMkgwyNt8xYoHLVkdf4XY6Tcd2GgNYyRshNXeTUcwlz5qXQV79yzPMVh6Exi5JV+++gJx2BWqVwGDSvE8ccjppTp1tCCx2D88NM2hpOs1hMp9hVtUipSzPjQYGXiVE+i9jWVbA4alXytjRzJstrqqTL93ebnmhHfBeU/gmRGzJtnjV5r+OOs83jsoECnObLkfoaTgEt5btw== 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 Fri 20-01-23 08:20:43, Suren Baghdasaryan wrote: > On Fri, Jan 20, 2023 at 12:52 AM Michal Hocko wrote: > > > > On Thu 19-01-23 10:52:03, Suren Baghdasaryan wrote: > > > On Thu, Jan 19, 2023 at 4:59 AM Michal Hocko wrote: > > > > > > > > On Mon 09-01-23 12:53:34, Suren Baghdasaryan wrote: > > > > > call_rcu() can take a long time when callback offloading is enabled. > > > > > Its use in the vm_area_free can cause regressions in the exit path when > > > > > multiple VMAs are being freed. To minimize that impact, place VMAs into > > > > > a list and free them in groups using one call_rcu() call per group. > > > > > > > > After some more clarification I can understand how call_rcu might not be > > > > super happy about thousands of callbacks to be invoked and I do agree > > > > that this is not really optimal. > > > > > > > > On the other hand I do not like this solution much either. > > > > VM_AREA_FREE_LIST_MAX is arbitrary and it won't really help all that > > > > much with processes with a huge number of vmas either. It would still be > > > > in housands of callbacks to be scheduled without a good reason. > > > > > > > > Instead, are there any other cases than remove_vma that need this > > > > batching? We could easily just link all the vmas into linked list and > > > > use a single call_rcu instead, no? This would both simplify the > > > > implementation, remove the scaling issue as well and we do not have to > > > > argue whether VM_AREA_FREE_LIST_MAX should be epsilon or epsilon + 1. > > > > > > Yes, I agree the solution is not stellar. I wanted something simple > > > but this is probably too simple. OTOH keeping all dead vm_area_structs > > > on the list without hooking up a shrinker (additional complexity) does > > > not sound too appealing either. > > > > I suspect you have missed my idea. I do not really want to keep the list > > around or any shrinker. It is dead simple. Collect all vmas in > > remove_vma and then call_rcu the whole list at once after the whole list > > (be it from exit_mmap or remove_mt). See? > > Yes, I understood your idea but keeping dead objects until the process > exits even when the system is low on memory (no shrinkers attached) > seems too wasteful. If we do this I would advocate for attaching a > shrinker. I am still not sure we are on the same page here. No, vmas shouldn't lay around un ntil the process exit. I am really suggesting queuing only for remove_vma paths. You can have a different rcu callback than the one used for trivial single vma removal paths. -- Michal Hocko SUSE Labs