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 6405CC761A6 for ; Tue, 28 Mar 2023 18:35:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229782AbjC1Sfv (ORCPT ); Tue, 28 Mar 2023 14:35:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39016 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229778AbjC1Sfr (ORCPT ); Tue, 28 Mar 2023 14:35:47 -0400 Received: from mail-ed1-x52b.google.com (mail-ed1-x52b.google.com [IPv6:2a00:1450:4864:20::52b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A0ED31BF0 for ; Tue, 28 Mar 2023 11:35:44 -0700 (PDT) Received: by mail-ed1-x52b.google.com with SMTP id ew6so53477184edb.7 for ; Tue, 28 Mar 2023 11:35:44 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cmpxchg-org.20210112.gappssmtp.com; s=20210112; t=1680028543; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=o2hU/6GK4yHeI2E04kJ+wsLD2zzLn1ZOn5QkCTAS5dA=; b=s0OoCPYdYEkWiMM8TXR/F3G9QugCTOtdgkWp/fAicaUkKXgp2XFtYk3zAUJDnqMevi Xf3+4b4fd5Hu48QoqkKSoCVZsT/Yu/N42Wa9Xnu6CA1219jcL+oRyO5XLEoidveTUKxo n9LN1JGvmoY8hBOw5A5+2YwYwtSgihqAfZHA/SSCzYsNIbb59Gr3mxUyfBoQLyigm3lG H5c/SlIDP4jZ6S555S4kX6KlRLshghyMMwqgBANA/rYnynD/kB+E28gcQIpx3ZCw4xvH 0Ozo6mqt8M0TtOo4/jZmtibYgtdp6nIfHpBDsPH0Xk+R5aSBpV0qEeiqa9Sdjd6u/uQ6 FU2w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680028543; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=o2hU/6GK4yHeI2E04kJ+wsLD2zzLn1ZOn5QkCTAS5dA=; b=b9VNNhcLJ317PkkbXsIIaTmls44V6n7WiEw2TgsfLkwRXZtA+xPdUisEUX1pbGgosn 5ro29RVe3r5xVKZntHSrNtOYsPBg2/Zi6LqUwrLO5/zJ2mG42XzoyEU9+paY7bWj/9iG bB6Y2IG9O5H8XbQtIpJynF8D95nceQfMDIA/EakOtYdXtEZVSjkFq+r7wSqHZp6AVwnT FsIOGXYCsNQmJm82kLSUSDnGg9VLVfbWqhz9edLlEtD96RXdseNjb0e3B1B+VAC55Q5A TA2DIH0bbdU6asjNKaopgWRTacD1BamLfjjh7RXXJKGY+O41VWADQPEcb+dLwYAGHwTm J8eA== X-Gm-Message-State: AAQBX9e5LuNcSHIuWhpdUD3OkT79UevJ+oo3rLBIdJe/Yyx0GxpC9rWy QVn7zjSjLk2Ag7GQH16XNWRV+w== X-Google-Smtp-Source: AKy350bYttSe2oGRVQfhpmdTk3tJEKqV5AnnS8nas8nc2Mr9yRQPwSpOo1ua8Z0xDEcEaG7DPr+yeQ== X-Received: by 2002:a17:907:7e8e:b0:932:dae5:2af9 with SMTP id qb14-20020a1709077e8e00b00932dae52af9mr22308243ejc.51.1680028543196; Tue, 28 Mar 2023 11:35:43 -0700 (PDT) Received: from localhost ([2a02:8070:6387:ab20:5139:4abd:1194:8f0e]) by smtp.gmail.com with ESMTPSA id xh1-20020a170906da8100b0093f83562f09sm4460301ejb.87.2023.03.28.11.35.42 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Mar 2023 11:35:43 -0700 (PDT) Date: Tue, 28 Mar 2023 14:35:41 -0400 From: Johannes Weiner To: Yosry Ahmed Cc: Tejun Heo , Josef Bacik , Jens Axboe , Zefan Li , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , Michal =?iso-8859-1?Q?Koutn=FD?= , Vasily Averin , cgroups@vger.kernel.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, bpf@vger.kernel.org Subject: Re: [PATCH v1 6/9] memcg: sleep during flushing stats in safe contexts Message-ID: References: <20230328061638.203420-1-yosryahmed@google.com> <20230328061638.203420-7-yosryahmed@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230328061638.203420-7-yosryahmed@google.com> Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Tue, Mar 28, 2023 at 06:16:35AM +0000, Yosry Ahmed wrote: > @@ -642,24 +642,57 @@ static void __mem_cgroup_flush_stats(void) > * from memcg flushers (e.g. reclaim, refault, etc). > */ > if (atomic_xchg(&stats_flush_ongoing, 1)) > - return; > + return false; > > WRITE_ONCE(flush_next_time, jiffies_64 + 2*FLUSH_TIME); > - cgroup_rstat_flush_atomic(root_mem_cgroup->css.cgroup); > + return true; > +} > + > +static void mem_cgroup_post_stats_flush(void) > +{ > atomic_set(&stats_flush_threshold, 0); > atomic_set(&stats_flush_ongoing, 0); > } > > -void mem_cgroup_flush_stats(void) > +static bool mem_cgroup_should_flush_stats(void) > { > - if (atomic_read(&stats_flush_threshold) > num_online_cpus()) > - __mem_cgroup_flush_stats(); > + return atomic_read(&stats_flush_threshold) > num_online_cpus(); > +} > + > +/* atomic functions, safe to call from any context */ > +static void __mem_cgroup_flush_stats_atomic(void) > +{ > + if (mem_cgroup_pre_stats_flush()) { > + cgroup_rstat_flush_atomic(root_mem_cgroup->css.cgroup); > + mem_cgroup_post_stats_flush(); > + } > +} I'm afraid I wasn't very nuanced with my complaint about the bool parameter in the previous version. In this case, when you can do a common helper for a couple of API functions defined right below it, and the callers don't spread throughout the codebase, using bools makes things simpler while still being easily understandable: static void do_flush_stats(bool may_sleep) { if (atomic_xchg(&stats_flush_ongoing, 1)) return; WRITE_ONCE(flush_next_time, jiffies_64 + 2*FLUSH_TIME); atomic_set(&stats_flush_threshold, 0); if (!may_sleep) cgroup_rstat_flush_atomic(root_mem_cgroup->css.cgroup); else cgroup_rstat_flush(root_mem_cgroup->css.cgroup); atomic_set(&stats_flush_ongoing, 0); } void mem_cgroup_flush_stats(void) { if (atomic_read(&stats_flush_threshold) > num_online_cpus()) do_flush_stats(true); } void mem_cgroup_flush_stats_atomic(void) { if (atomic_read(&stats_flush_threshold) > num_online_cpus()) do_flush_stats(false); } > void mem_cgroup_flush_stats_ratelimited(void) > { > if (time_after64(jiffies_64, READ_ONCE(flush_next_time))) > - mem_cgroup_flush_stats(); > + mem_cgroup_flush_stats_atomic(); > +} This should probably be mem_cgroup_flush_stats_atomic_ratelimited(). (Whee, kinda long, but that's alright. Very specialized caller...) Btw, can you guys think of a reason against moving the threshold check into the common function? It would then apply to the time-limited flushes as well, but that shouldn't hurt anything. This would make the code even simpler: static void do_flush_stats(bool may_sleep) { if (atomic_read(&stats_flush_threshold) <= num_online_cpus()) return; if (atomic_xchg(&stats_flush_ongoing, 1)) return; WRITE_ONCE(flush_next_time, jiffies_64 + 2*FLUSH_TIME); atomic_set(&stats_flush_threshold, 0); if (!may_sleep) cgroup_rstat_flush_atomic(root_mem_cgroup->css.cgroup); else cgroup_rstat_flush(root_mem_cgroup->css.cgroup); atomic_set(&stats_flush_ongoing, 0); } void mem_cgroup_flush_stats(void) { do_flush_stats(true); } void mem_cgroup_flush_stats_atomic(void) { do_flush_stats(false); } void mem_cgroup_flush_stats_atomic_ratelimited(void) { if (time_after64(jiffies_64, READ_ONCE(flush_next_time))) do_flush_stats(false); } > @@ -2845,7 +2845,7 @@ static void prepare_scan_count(pg_data_t *pgdat, struct scan_control *sc) > * Flush the memory cgroup stats, so that we read accurate per-memcg > * lruvec stats for heuristics. > */ > - mem_cgroup_flush_stats(); > + mem_cgroup_flush_stats_atomic(); I'm thinking this one could be non-atomic as well. It's called fairly high up in reclaim without any locks held.