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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 99394C38142 for ; Fri, 27 Jan 2023 06:58:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232067AbjA0G6n (ORCPT ); Fri, 27 Jan 2023 01:58:43 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56666 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232078AbjA0G6h (ORCPT ); Fri, 27 Jan 2023 01:58:37 -0500 Received: from smtp-out1.suse.de (smtp-out1.suse.de [IPv6:2001:67c:2178:6::1c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 918F01E5E4; Thu, 26 Jan 2023 22:58:35 -0800 (PST) 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 2EAAD21BB3; Fri, 27 Jan 2023 06:58:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1674802714; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=g+E5xBJ3UOLpBqu7Q/7w5cQuQLqZh3v0sZZi4etorHM=; b=YGGNoTNQSsBG2crAEEf577da9ZlMzCQfCzd1kLQO55iHcOKNihErXr7ZcEAiMcI3Nhh4OP Po3w6eO0WJ6HNVdNfx5oWkuZax3loRjgY6iHwTSCaqhEVGvHYBknYbOSpV4VkJ4h2CvyAp V4rM4uxPXKoxjeLA7/drrCxbfEz8Wb4= 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 0C31C1336F; Fri, 27 Jan 2023 06:58:34 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap2.suse-dmz.suse.de with ESMTPSA id fJ2xABp202OPUAAAMHmgww (envelope-from ); Fri, 27 Jan 2023 06:58:34 +0000 Date: Fri, 27 Jan 2023 07:58:32 +0100 From: Michal Hocko To: Marcelo Tosatti Cc: Roman Gushchin , Leonardo =?iso-8859-1?Q?Br=E1s?= , Johannes Weiner , Shakeel Butt , Muchun Song , Andrew Morton , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 0/5] Introduce memcg_stock_pcp remote draining Message-ID: References: <20230125073502.743446-1-leobras@redhat.com> <9e61ab53e1419a144f774b95230b789244895424.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 26-01-23 21:32:18, Marcelo Tosatti wrote: > On Thu, Jan 26, 2023 at 08:20:46PM +0100, Michal Hocko wrote: > > On Thu 26-01-23 15:03:43, Marcelo Tosatti wrote: > > > On Thu, Jan 26, 2023 at 08:41:34AM +0100, Michal Hocko wrote: > > > > On Wed 25-01-23 15:14:48, Roman Gushchin wrote: > > > > > On Wed, Jan 25, 2023 at 03:22:00PM -0300, Marcelo Tosatti wrote: > > > > > > On Wed, Jan 25, 2023 at 08:06:46AM -0300, Leonardo Brás wrote: > > > > > > > On Wed, 2023-01-25 at 09:33 +0100, Michal Hocko wrote: > > > > > > > > On Wed 25-01-23 04:34:57, Leonardo Bras wrote: > > > > > > > > > Disclaimer: > > > > > > > > > a - The cover letter got bigger than expected, so I had to split it in > > > > > > > > > sections to better organize myself. I am not very confortable with it. > > > > > > > > > b - Performance numbers below did not include patch 5/5 (Remove flags > > > > > > > > > from memcg_stock_pcp), which could further improve performance for > > > > > > > > > drain_all_stock(), but I could only notice the optimization at the > > > > > > > > > last minute. > > > > > > > > > > > > > > > > > > > > > > > > > > > 0 - Motivation: > > > > > > > > > On current codebase, when drain_all_stock() is ran, it will schedule a > > > > > > > > > drain_local_stock() for each cpu that has a percpu stock associated with a > > > > > > > > > descendant of a given root_memcg. > > > > > > > > > > Do you know what caused those drain_all_stock() calls? I wonder if we should look > > > > > into why we have many of them and whether we really need them? > > > > > > > > > > It's either some user's actions (e.g. reducing memory.max), either some memcg > > > > > is entering pre-oom conditions. In the latter case a lot of drain calls can be > > > > > scheduled without a good reason (assuming the cgroup contain multiple tasks running > > > > > on multiple cpus). > > > > > > > > I believe I've never got a specific answer to that. We > > > > have discussed that in the previous version submission > > > > (20221102020243.522358-1-leobras@redhat.com and specifically > > > > Y2TQLavnLVd4qHMT@dhcp22.suse.cz). Leonardo has mentioned a mix of RT and > > > > isolcpus. I was wondering about using memcgs in RT workloads because > > > > that just sounds weird but let's say this is the case indeed. > > > > > > This could be the case. You can consider an "edge device" where it is > > > necessary to run a RT workload. It might also be useful to run > > > non realtime applications on the same system. > > > > > > > Then an RT task or whatever task that is running on an isolated > > > > cpu can have pcp charges. > > > > > > Usually the RT task (or more specifically the realtime sensitive loop > > > of the application) runs entirely on userspace. But i suppose there > > > could be charges on application startup. > > > > What is the role of memcg then? If the memory limit is in place and the > > workload doesn't fit in then it will get reclaimed during start up and > > memory would need to be refaulted if not mlocked. If it is mlocked then > > the limit cannot be enforced and the start up would likely fail as a > > result of the memcg oom killer. > > 1) Application which is not time sensitive executes on isolated CPU, > with memcg control enabled. Per-CPU stock is created. > > 2) App with memcg control enabled exits, per-CPU stock is not drained. > > 3) Latency sensitive application starts, isolated per-CPU has stock to > be drained, and: > > /* > * Drains all per-CPU charge caches for given root_memcg resp. subtree > * of the hierarchy under it. > */ > static void drain_all_stock(struct mem_cgroup *root_memcg) No, this is not really answering my question. See Y9LQ615H13RmG7wL@dhcp22.suse.cz which already explains how the draining would be triggered. This is not really happening on any operation. I am really asking for specific workloads which are running multiple processes on a mix of isolated and non-isolated cpus yet they share memcg so that they can interfere. The consequences of the common memcg are described above. -- Michal Hocko SUSE Labs