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 082DBC433F5 for ; Tue, 7 Dec 2021 07:15:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229470AbhLGHSp (ORCPT ); Tue, 7 Dec 2021 02:18:45 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54384 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229596AbhLGHSm (ORCPT ); Tue, 7 Dec 2021 02:18:42 -0500 Received: from mail-lj1-x236.google.com (mail-lj1-x236.google.com [IPv6:2a00:1450:4864:20::236]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3EC7FC061746 for ; Mon, 6 Dec 2021 23:15:12 -0800 (PST) Received: by mail-lj1-x236.google.com with SMTP id p8so25694972ljo.5 for ; Mon, 06 Dec 2021 23:15:12 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=JeLlEalXSQHW4pH2trtzzJDx6YYnAF08ckO/i6n2PyA=; b=SYj34d/hxJKfq8EbSGQE2cpAxSibC6df+us5qeCDougZMKek8E4/t6ldI2shF2MZnF 6UIphA+wzSY8hgwgCCx+mMA3w25N7z7n+oQyDpJZNdQcGSjsmHMCgcYOQ3j4mF/lfrCt W7KKBRZUT1Ar3N0hizzhJr/8MleLpp4BXs+ikkCrJCiyaMrs5lhP3g+lBjvokFFdVO0D zliqi/bBTOtRB5FRrsiF0rtcMzmG5/6skvbYHndDnafnzaybiBkG73gNYZVy9rBkIJYK P4A+pVYqf6oZ4vnzOgoTmyellVvHpgzEV4i2Hod3I75Q9hjkKLPSRj3chdCa4hLVp6AT La1g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=JeLlEalXSQHW4pH2trtzzJDx6YYnAF08ckO/i6n2PyA=; b=OfV0ZcqFMbXtAj0Py+LXUh5at5+ROkOsDrW2gIEsSaaAXf7YqpuN0QH664N7gIYyPY vcHQPLin5LACe+wjcVfBUTOvA+uj0KTpvF1+cuRTi+eIaSuRlhYhilOgD0we+pWHyoXd guDlykFXHqQX8j0SbxYe6fUMRHY5NTYDr9sIEhzAFal2aYv3z/+9uGQFqUA7xnquoMey Jox3JLOdCD4RLudnHK0dzkjIx3ds0mUue7R3ql2VwnqWOrG1ONYxYHHoVd9WQi6yFmWg CxZIAkIe2+riOBBjmXsJY/5KawTbiqv+HP46gdvoa0eOaVR4O0hrXGy0Xbc77PwH8/cM 3wig== X-Gm-Message-State: AOAM531ir9lmUYY2+JZb5L/qaEE08ytsvb8/nCkfzeYZVF9ABOZsJtke z8nAMdOTQ5mfIFRlw+YQtN7RSgM8WFeqRXvKMzfx0A== X-Google-Smtp-Source: ABdhPJwD7St5XCs0KtsZ7B4kQrin00YT33yrHoQP8SuXlTurcS6UiF5SVM2kIX/jVUXjXi6ZmXrY/VK8VWLJc333RG4= X-Received: by 2002:a05:651c:1790:: with SMTP id bn16mr40860622ljb.475.1638861310287; Mon, 06 Dec 2021 23:15:10 -0800 (PST) MIME-Version: 1.0 References: <20211202150614.22440-1-mgorman@techsingularity.net> <20211202165220.GZ3366@techsingularity.net> <20211203090137.GA3366@techsingularity.net> <20211203190807.GE3366@techsingularity.net> <20211206112545.GF3366@techsingularity.net> In-Reply-To: <20211206112545.GF3366@techsingularity.net> From: Shakeel Butt Date: Mon, 6 Dec 2021 23:14:58 -0800 Message-ID: Subject: Re: [PATCH v4 1/1] mm: vmscan: Reduce throttling due to a failure to make progress To: Mel Gorman Cc: Andrew Morton , Michal Hocko , Vlastimil Babka , Alexey Avramov , Rik van Riel , Mike Galbraith , Darrick Wong , regressions@lists.linux.dev, Linux-fsdevel , Linux-MM , LKML Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Dec 6, 2021 at 3:25 AM Mel Gorman wrote: > > On Sun, Dec 05, 2021 at 10:06:27PM -0800, Shakeel Butt wrote: > > On Fri, Dec 3, 2021 at 11:08 AM Mel Gorman wrote: > > > > > [...] > > > > I am in agreement with the motivation of the whole series. I am just > > > > making sure that the motivation of VMSCAN_THROTTLE_NOPROGRESS based > > > > throttle is more than just the congestion_wait of > > > > mem_cgroup_force_empty_write. > > > > > > > > > > The commit that primarily targets congestion_wait is 8cd7c588decf > > > ("mm/vmscan: throttle reclaim until some writeback completes if > > > congested"). The series recognises that there are other reasons why > > > reclaim can fail to make progress that is not directly writeback related. > > > > > > > I agree with throttling for VMSCAN_THROTTLE_[WRITEBACK|ISOLATED] > > reasons. Please explain why we should throttle for > > VMSCAN_THROTTLE_NOPROGRESS? Also 69392a403f49 claims "Direct reclaim > > primarily is throttled in the page allocator if it is failing to make > > progress.", can you please explain how? > > It could happen if the pages on the LRU are being reactivated continually > or holding an elevated reference count for some reason (e.g. gup, > page migration etc). The event is probably transient, hence the short > throttling. > What's the worst that can happen if the kernel doesn't throttle at all for these transient scenarios? Premature oom-kills? The kernel already has some protection against such situations with retries i.e. consecutive 16 unsuccessful reclaim tries have to fail to give up the reclaim. Anyways, I have shared my view which is 'no need to throttle at all for no-progress reclaims for now and course correct if there are complaints in future' but will not block the patch. thanks, Shakeel