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 5C2A6C433EF for ; Tue, 5 Apr 2022 00:49:24 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id AA0BD6B0071; Mon, 4 Apr 2022 20:49:13 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id A75246B0073; Mon, 4 Apr 2022 20:49:13 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8C8B06B0074; Mon, 4 Apr 2022 20:49:13 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0135.hostedemail.com [216.40.44.135]) by kanga.kvack.org (Postfix) with ESMTP id 79E706B0071 for ; Mon, 4 Apr 2022 20:49:13 -0400 (EDT) Received: from smtpin29.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 3E199824CA0B for ; Tue, 5 Apr 2022 00:49:03 +0000 (UTC) X-FDA: 79320990966.29.D185983 Received: from mail-pl1-f169.google.com (mail-pl1-f169.google.com [209.85.214.169]) by imf29.hostedemail.com (Postfix) with ESMTP id BB48E120018 for ; Tue, 5 Apr 2022 00:49:02 +0000 (UTC) Received: by mail-pl1-f169.google.com with SMTP id i11so9530586plg.12 for ; Mon, 04 Apr 2022 17:49:02 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=y7CfRmOu2mFNhlP27BBXPAgEnRTv2JAfJlw4FzS8AkI=; b=Z/ADUipXSo6cCCoApgoWmuri8ib7Z2ZRmbnR54h8/VrIGaueK5QGu/WZtyWNFshPcu iAUxF22NOgckmUzcLG64u90kuydHGTVHt9OYXf690baDj9sOYSCj/jaZkbYXeWXHpMmB fAHEsMsaWg7XOguwyTv9/4z8MTuyMLKrHnwV08vQpUkIZUwgrbHKz3AVmSD3jtcNlM/x 0UinNkINbSntmhwlU0tlzyGj/QAvnPpxiM0jFhKpPSABVsY/8/XIx1H5kYyTNNFKFogR jNANubjJDZQhCftsvAm3pWtbim5rG5UTWikV3yCU0eXPRTt1v5MNXIOEz9cyijS6kP55 XDvQ== 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=y7CfRmOu2mFNhlP27BBXPAgEnRTv2JAfJlw4FzS8AkI=; b=V8a1f9uCn/6PJ0tV4g04NPFplz724z+5tlYb5DN0QHI5b/X2/Kj2MgomY7lNsCD4Kk XPGl15x/uo+o1mqcIq5RuRuuFb6frRHieLAa1A17bAnp2W6jbSzBNLS45gs60WJh1a6b qEJMZqAAdvOekGuMusDvSP2zz3rIR/pGsk9PINjOsX2F58x93Mvs8/xCw9XLAnQayAnl omnUXbCQo1Gqxh6LE3RAED5ObBTOI9mOyI1JHIg3zQhJff3fJS913z63d3SP7ccDYXTZ pwc1cqnADU34japbb92Ttq4+F7HwmxpkpDiaT19Xn0yTGz/fdee1x+T6JdGx14Mjp3cH 4L0g== X-Gm-Message-State: AOAM531tBj2v+pWVIaGgjDamlkoZ2uJllxAIWbk5H79UohTKiMTJVgN9 UU170tdelutUe2rd5I+KTMOUhG6zM7scScyetyM= X-Google-Smtp-Source: ABdhPJyefORiL8A7gzvpS7dFgoDZqSwDNKY91Ji/hlxmeFS27O7LqO1jBzOIggw1AkXZ8Y44Dm+GJ8fQng2R1BpN3QQ= X-Received: by 2002:a17:90a:5298:b0:1ca:7fb3:145 with SMTP id w24-20020a17090a529800b001ca7fb30145mr1036706pjh.200.1649119741666; Mon, 04 Apr 2022 17:49:01 -0700 (PDT) MIME-Version: 1.0 References: <20220404200250.321455-1-shy828301@gmail.com> In-Reply-To: From: Yang Shi Date: Mon, 4 Apr 2022 17:48:49 -0700 Message-ID: Subject: Re: [v3 PATCH 0/8] Make khugepaged collapse readonly FS THP more consistent To: Matthew Wilcox Cc: Vlastimil Babka , "Kirill A. Shutemov" , Miaohe Lin , Song Liu , Rik van Riel , Zi Yan , "Theodore Ts'o" , Andrew Morton , Linux MM , Linux FS-devel Mailing List , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: waempp5wanm9s81dn5fqj7uqzbu9mjbs Authentication-Results: imf29.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b="Z/ADUipX"; spf=pass (imf29.hostedemail.com: domain of shy828301@gmail.com designates 209.85.214.169 as permitted sender) smtp.mailfrom=shy828301@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: BB48E120018 X-HE-Tag: 1649119742-655193 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 Mon, Apr 4, 2022 at 5:16 PM Matthew Wilcox wrote: > > On Mon, Apr 04, 2022 at 01:02:42PM -0700, Yang Shi wrote: > > The readonly FS THP relies on khugepaged to collapse THP for suitable > > vmas. But it is kind of "random luck" for khugepaged to see the > > readonly FS vmas (see report: https://lore.kernel.org/linux-mm/00f195d4-d039-3cf2-d3a1-a2c88de397a0@suse.cz/) since currently the vmas are registered to khugepaged when: > > I still don't see the point. The effort should be put into > supporting large folios, not in making this hack work better. The series makes sense even though the hack is replaced by large folios IMHO. The problem is the file VMAs may be not registered by khugepaged consistently for some THP modes, for example, always, regardless of whether it's readonly or the hack is gone or not. IIUC even though the hack is replaced by the large folios, we still have khugepaged to collapse pmd-mappable huge pages for both anonymous vmas and file vmas, right? Or are you thinking about killing khugepaged soon with supporting large folios? Anyway it may make things clearer if the cover letter is rephrased to: When khugepaged collapses file THPs, its behavior is not consistent. It is kind of "random luck" for khugepaged to see the file vmas (see report: https://lore.kernel.org/linux-mm/00f195d4-d039-3cf2-d3a1-a2c88de397a0@suse.cz/) since currently the vmas are registered to khugepaged when: - Anon huge pmd page fault - VMA merge - MADV_HUGEPAGE - Shmem mmap If the above conditions are not met, even though khugepaged is enabled it won't see any file vma at all. MADV_HUGEPAGE could be specified explicitly to tell khugepaged to collapse this area, but when khugepaged mode is "always" it should scan suitable vmas as long as VM_NOHUGEPAGE is not set. So make sure file vmas are registered to khugepaged to make the behavior more consistent.