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 EE4F7C433FE for ; Wed, 16 Nov 2022 14:57:19 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6FA666B0072; Wed, 16 Nov 2022 09:57:19 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 6AA796B0073; Wed, 16 Nov 2022 09:57:19 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 599468E0001; Wed, 16 Nov 2022 09:57:19 -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 4670D6B0072 for ; Wed, 16 Nov 2022 09:57:19 -0500 (EST) Received: from smtpin26.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay05.hostedemail.com (Postfix) with ESMTP id 2269040708 for ; Wed, 16 Nov 2022 14:57:19 +0000 (UTC) X-FDA: 80139608598.26.6E42EC0 Received: from smtp-out2.suse.de (smtp-out2.suse.de [195.135.220.29]) by imf23.hostedemail.com (Postfix) with ESMTP id 810B3140009 for ; Wed, 16 Nov 2022 14:57:17 +0000 (UTC) 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-out2.suse.de (Postfix) with ESMTPS id 98D361F94F; Wed, 16 Nov 2022 14:57:15 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1668610635; 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=3vl4NdpO4irC1eRJoV821C0JFp7+4A15d5hSm1FQvTo=; b=eqaB6EP2GKiw5QP6JiW0cWOM1NG4anZRyh1calWKdEwUX95RbEKck+SxlKqWruwGYlnjRW InAsn8C+8XCSZZ23Mcg3b7PsV6E7utY9JOJX4lXDMQlPNUCOIwlxjZtQp2QRMW+DkxU1bQ lzj7mbU+Msd0KWWV5/hZ7unfoL4q6B4= 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 7A24113480; Wed, 16 Nov 2022 14:57:15 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id qwJoG0v6dGOYYgAAMHmgww (envelope-from ); Wed, 16 Nov 2022 14:57:15 +0000 Date: Wed, 16 Nov 2022 15:57:14 +0100 From: Michal Hocko To: Zhongkun He Cc: Andrew Morton , corbet@lwn.net, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, linux-doc@vger.kernel.org Subject: Re: [External] Re: [PATCH v2] mm: add new syscall pidfd_set_mempolicy(). Message-ID: References: <20221111084051.2121029-1-hezhongkun.hzk@bytedance.com> <20221111112732.30e1696bcd0d5b711c188a9a@linux-foundation.org> <3a3b4f5b-14d1-27d8-7727-cf23da90988f@bytedance.com> <82c9c89c-aee2-08a3-e562-359631bb0137@bytedance.com> <0bd0b744-3d97-b4c3-a4fb-6040f8f8024a@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0bd0b744-3d97-b4c3-a4fb-6040f8f8024a@bytedance.com> ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1668610637; a=rsa-sha256; cv=none; b=STY2G4TatgMNDYNbdD81jD6oH0s+IfB9NFprTxa5yQjmt76vIOUrI7w1go++4Q2lP75dOj 9kx4t8pqjMcgff7gK+1BFLBm0Gg5OdAHHLlwkOMrKnF7ZVrIWfeX5s8U5cXiKMnvm4cLQ6 zPCIJa9yp5yH2AjIZMWsFOVe5cHs0yE= ARC-Authentication-Results: i=1; imf23.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=eqaB6EP2; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf23.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1668610637; 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=3vl4NdpO4irC1eRJoV821C0JFp7+4A15d5hSm1FQvTo=; b=2X85v8qv4l6miLvL9No1Ep9QEnd6szF/f1h3UdqH1X8kYDDbbEcuUshN6csHb5TYffUaUB 17mSU96UXJ860+fa8GGwPN2xTWGrQJlu3RasTy8pM7Vy3VtpKERM5LUeMfGG9Z4rpMCVQH 7Dvm4n4iQajTHDfONTd60bqqagfrM/0= X-Rspamd-Queue-Id: 810B3140009 Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=suse.com header.s=susede1 header.b=eqaB6EP2; dmarc=pass (policy=quarantine) header.from=suse.com; spf=pass (imf23.hostedemail.com: domain of mhocko@suse.com designates 195.135.220.29 as permitted sender) smtp.mailfrom=mhocko@suse.com X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 87ioattouz4sfjjg5a5t88tfzzpsn6ia X-HE-Tag: 1668610637-653231 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 Wed 16-11-22 19:28:10, Zhongkun He wrote: > Hi Michal, I've done the performance testing, please check it out. > > > > Yes this is all understood but the level of the overhead is not really > > > clear. So the question is whether this will induce a visible overhead. > > > Because from the maintainability point of view it is much less costly to > > > have a clear life time model. Right now we have a mix of reference > > > counting and per-task requirements which is rather subtle and easy to > > > get wrong. In an ideal world we would have get_vma_policy always > > > returning a reference counted policy or NULL. If we really need to > > > optimize for cache line bouncing we can go with per cpu reference > > > counters (something that was not available at the time the mempolicy > > > code has been introduced). > > > > > > So I am not saying that the task_work based solution is not possible I > > > just think that this looks like a good opportunity to get from the > > > existing subtle model. > > Test tools: > numactl -m 0-3 ./run-mmtests.sh -n -c configs/config-workload- > aim9-pagealloc test_name > > Modification: > Get_vma_policy(), get_task_policy() always returning a reference > counted policy, except for the static policy(default_policy and > preferred_node_policy[nid]). It would be better to add the patch that has been tested. > All vma manipulation is protected by a down_read, so mpol_get() > can be called directly to take a refcount on the mpol. but there > is no lock in task->mempolicy context. > so task->mempolicy should be protected by task_lock. > > struct mempolicy *get_task_policy(struct task_struct *p) > { > struct mempolicy *pol; > int node; > > if (p->mempolicy) { > task_lock(p); > pol = p->mempolicy; > mpol_get(pol); > task_unlock(p); > if (pol) > return pol; > } One way to deal with that would be to use a similar model as css_tryget Btw. have you tried to profile those slowdowns to identify hotspots? Thanks -- Michal Hocko SUSE Labs