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 0C888C761A6 for ; Tue, 28 Mar 2023 19:06:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229685AbjC1TGK (ORCPT ); Tue, 28 Mar 2023 15:06:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33152 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229617AbjC1TGJ (ORCPT ); Tue, 28 Mar 2023 15:06:09 -0400 Received: from mail-ed1-x536.google.com (mail-ed1-x536.google.com [IPv6:2a00:1450:4864:20::536]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BF31A2719 for ; Tue, 28 Mar 2023 12:06:06 -0700 (PDT) Received: by mail-ed1-x536.google.com with SMTP id ew6so53799230edb.7 for ; Tue, 28 Mar 2023 12:06:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cmpxchg-org.20210112.gappssmtp.com; s=20210112; t=1680030365; h=in-reply-to:content-transfer-encoding:content-disposition :mime-version:references:message-id:subject:cc:to:from:date:from:to :cc:subject:date:message-id:reply-to; bh=WQyIrdKCsHvb8zLTh5h/QnKicAPnjV8XyfAnbUhyqtc=; b=eGikLsGLFoVUkW6GbVQkOFBoDpp+W99UiFbI/1642zWEFZ3juLQaRaltNCn2wU02D4 YL7jzA8mTQn67wxUeBcnWhvdMnr7A5ebifJPOyfQPIkEOzJxi6194cbH6C6j3kKl8Ywl XY3zE4et0pjZlCrDxONVchgaIVK8GzX60e6GQTpdrsOE/QF3qkhQESQeWnFpo7qhv9f7 3d5b6XKEPzhosboezNX9Lu3mnNa36lMRugddSdn5yJmIE4bQr6mBDyVxDY/HWbX3+3KJ cJRFP4ssIfd/HvC3ZbE6cl+jYuymOoi7hkVc8hvAod8Y9FnsSo8mTPul4jkMAP7OITxv Ta/A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1680030365; h=in-reply-to:content-transfer-encoding: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=WQyIrdKCsHvb8zLTh5h/QnKicAPnjV8XyfAnbUhyqtc=; b=XI2Y04BjBw5fG/y+sNKK1EGN0WQZyDI0pq0m55PwcFkJyCsp0kwpdWLdtfi6mimbGy CpnA1qnQ0Etb0HXhitV6hEWnklJrA9DPlbzMngGh9Ivb56j2zBlEH4Dy/PeP8zIVEwFI hkkHUxRwrGbDPNIbfPuLOXYVI6iNKfRKojyrSLzxB4BV2sdcHqxv37qs9Ec6wJFu8sf5 dYSZSF+04I12+qnnGjeHvfZqlchBIJ5fo1Vc/CDVyEIu/sM1Yt5PcE7dta1njSLl2ILJ QXcqiC/BNTiMfjG3o1Y6DVRIUHVpH5QkenpJY5JudiyzbmEr6RdCkjZzB4Hj+/ir7uzB SybQ== X-Gm-Message-State: AAQBX9f1RuTZZb1ObnfNMCzaEhp3E6wpMLdnTVri7Fscudj30TIqoO8H Ibo/UNjj6B6OSjGj2942wqcTPw== X-Google-Smtp-Source: AKy350aw3p2OspiyiuuWmLGeQQA0Ae4PemXrygP5k1HGpsqdCzFAOkR4Ju/Zc6bJrxyK3dozuSVLvA== X-Received: by 2002:a17:907:d402:b0:930:ca4d:f2bf with SMTP id vi2-20020a170907d40200b00930ca4df2bfmr19816432ejc.54.1680030365312; Tue, 28 Mar 2023 12:06:05 -0700 (PDT) Received: from localhost ([2a02:8070:6387:ab20:5139:4abd:1194:8f0e]) by smtp.gmail.com with ESMTPSA id xh9-20020a170906da8900b009447277c26fsm3069805ejb.72.2023.03.28.12.06.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Mar 2023 12:06:05 -0700 (PDT) Date: Tue, 28 Mar 2023 15:06:03 -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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Tue, Mar 28, 2023 at 11:45:19AM -0700, Yosry Ahmed wrote: > On Tue, Mar 28, 2023 at 11:35 AM Johannes Weiner wrote: > > On Tue, Mar 28, 2023 at 06:16:35AM +0000, Yosry Ahmed wrote: > > > 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...) > > It should, but the following patch makes it non-atomic anyway, so I > thought I wouldn't clutter the diff by renaming it here and then > reverting it back in the next patch. > > There is an argument for maintaining a clean history tho in case the > next patch is reverted separately (which is the reason I put it in a > separate patch to begin with) -- so perhaps I should rename it here to > mem_cgroup_flush_stats_atomic_ratelimited () and back to > mem_cgroup_flush_stats_ratelimited() in the next patch, just for > consistency? Sounds good to me. It's pretty minor churn. > > 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: > > I think the point of having the threshold check outside the common > function is that the periodic flusher always flushes, regardless of > the threshold, to keep rstat flushing from critical contexts as cheap > as possible. Good point. Yeah, let's keep it separate then. > > > @@ -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. > > A later patch does exactly that. I put making the reclaim and refault > paths non-atomic in separate patches to easily revert them if we see a > regression. Let me know if this is too defensive and if you'd rather > have them squashed. No, good call. I should have just looked ahead first :-)