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 X-Spam-Level: X-Spam-Status: No, score=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5EC4CC352BE for ; Tue, 14 Apr 2020 21:35:32 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 09493206E9 for ; Tue, 14 Apr 2020 21:35:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=shutemov-name.20150623.gappssmtp.com header.i=@shutemov-name.20150623.gappssmtp.com header.b="hRvZ3q3j" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 09493206E9 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=shutemov.name Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 8FE4F8E0003; Tue, 14 Apr 2020 17:35:31 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 8AEEF8E0001; Tue, 14 Apr 2020 17:35:31 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 776BC8E0003; Tue, 14 Apr 2020 17:35:31 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0067.hostedemail.com [216.40.44.67]) by kanga.kvack.org (Postfix) with ESMTP id 5BE0E8E0001 for ; Tue, 14 Apr 2020 17:35:31 -0400 (EDT) Received: from smtpin18.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 0FF0F2494 for ; Tue, 14 Apr 2020 21:35:31 +0000 (UTC) X-FDA: 76707767262.18.hate03_1304582ace457 X-HE-Tag: hate03_1304582ace457 X-Filterd-Recvd-Size: 4484 Received: from mail-lj1-f193.google.com (mail-lj1-f193.google.com [209.85.208.193]) by imf50.hostedemail.com (Postfix) with ESMTP for ; Tue, 14 Apr 2020 21:35:30 +0000 (UTC) Received: by mail-lj1-f193.google.com with SMTP id z26so1402866ljz.11 for ; Tue, 14 Apr 2020 14:35:30 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=shutemov-name.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=jj2SfzpXG2vA6JlDKL4eiWHkk7cpfBu8IVq5OsaqiRc=; b=hRvZ3q3jq55HSrnCkkzeAGXrTsL41FHYn1NHzaoFXqmZ2lbV/tDRtYA+szFTAYL++r +x40YLtlUaHAd0iY4V7aUVJBSpUjdhHbK+Ld9VHczwxKML3hUcGWw0ke84L2CkBFo000 gjhpcvbO/YAYp6A++dcyJNSPMVxBKIwqXTmDUVQgVKJ2CaIXgOWoboB525DBWT77p6l4 NkaQk9XmEvimNONPKimGJtViDpiChtH18vH/T084/VMRr3ARuNqGl8ay1zi8SPoFTqBQ I0g5HXhNV0/ysU2bhAtPYjL/p/hTk01RxBXAeBWVWh7whYa4ydVyzwlInaoAz4kMLG9k YJDA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=jj2SfzpXG2vA6JlDKL4eiWHkk7cpfBu8IVq5OsaqiRc=; b=P+7o9IYoHylXhap4AczSBzPn0ad7dp6PjBiVJ7IgBYNZ0KGZdFBDUR3QXm3YgLxC6v ziB1mUholF4JEaaDm8W60sPUjgi1ehkATYjvSkwO0koBkbLpY83PuCwWjKgbQIY6vVlM TCj1qnGzWgWQ7fv/eLHaR6rLuI9HHaoUFGg2oWARGyVBO4w3eHbb/d8JtUdzQHRqaGXN vvv5L8kCnSYmW5VHUvuWLM1SB5daUwJZAsY2ssM/q8uXamwxaH585gfGD9B4C3HtavYP erQ01QOOrj23Gs20HOdBao108ZD86QAxikv0bLpfbwQyksiOX5SgE2u35fcKFMofdXXq Qcag== X-Gm-Message-State: AGi0PuYhXUaI68sf6jbumBLoAVQQSSiyP5Euixpy1j6dlFKsLTFq87tf t/4U6BOI/YQRAK4gc/R/HLrgY1kq2TQ= X-Google-Smtp-Source: APiQypLVgR917IPyg1HTf6YZfxptuXp5hCiH3thAs8A9VHxzojJCJhEzYrQLLbyXF5YtOE7TyA1xuQ== X-Received: by 2002:a2e:a310:: with SMTP id l16mr1283122lje.255.1586900128696; Tue, 14 Apr 2020 14:35:28 -0700 (PDT) Received: from box.localdomain ([86.57.175.117]) by smtp.gmail.com with ESMTPSA id x17sm9863062ljc.33.2020.04.14.14.35.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 14 Apr 2020 14:35:27 -0700 (PDT) Received: by box.localdomain (Postfix, from userid 1000) id B619D1029A3; Wed, 15 Apr 2020 00:35:26 +0300 (+03) Date: Wed, 15 Apr 2020 00:35:26 +0300 From: "Kirill A. Shutemov" To: John Hubbard Cc: "Kirill A. Shutemov" , akpm@linux-foundation.org, Andrea Arcangeli , Zi Yan , Yang Shi , Ralph Campbell , William Kucharski , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCHv3, RESEND 5/8] khugepaged: Allow to collapse a page shared across fork Message-ID: <20200414213526.ecn3zcgnqxoveddq@box> References: <20200413125220.663-1-kirill.shutemov@linux.intel.com> <20200413125220.663-6-kirill.shutemov@linux.intel.com> <0efcc512-6f12-1ff0-9885-871172fac766@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0efcc512-6f12-1ff0-9885-871172fac766@nvidia.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.002275, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Apr 13, 2020 at 01:48:22PM -0700, John Hubbard wrote: [Thanks for all your suggestions and corrections] > > + if (IS_ENABLED(CONFIG_DEBUG_VM) && expected_refcount > refcount) { > > + pr_err("expected_refcount: %d, refcount: %d\n", > > + expected_refcount, refcount); > > + dump_page(page, "Unexpected refcount"); > > > I see two issues with the pr_err() and the dump_page() call: > > 1. You probably want to rate limit this, otherwise you'll have a big > problem if lots of pages are pinned! Nope. Only if kernel is buggy. See below. > 2. Actually, I don't think you'd want to print anything at all here, even with > rate limiting, because doing so presumes that "unexpected" means "wrong". And I > think this patch doesn't expect to have GUP pins (or pin_user_pages() pins, ha), > but that doesn't mean that they're wrong to have. See condition. We only do it if refcount is *below* expected refcount. It should never happen. Pinned page would have refcount above expected. -- Kirill A. Shutemov