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, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, 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 F13B4C4332B for ; Fri, 20 Mar 2020 09:19:59 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B2ED520739 for ; Fri, 20 Mar 2020 09:19:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="P40kBnaT" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B2ED520739 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 4C4DA6B0003; Fri, 20 Mar 2020 05:19:59 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 475C96B0006; Fri, 20 Mar 2020 05:19:59 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 365316B0007; Fri, 20 Mar 2020 05:19:59 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0073.hostedemail.com [216.40.44.73]) by kanga.kvack.org (Postfix) with ESMTP id 1BAB36B0003 for ; Fri, 20 Mar 2020 05:19:59 -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 B1950824556B for ; Fri, 20 Mar 2020 09:19:58 +0000 (UTC) X-FDA: 76615193676.29.crib66_91489468ff13d X-HE-Tag: crib66_91489468ff13d X-Filterd-Recvd-Size: 4524 Received: from mail-io1-f51.google.com (mail-io1-f51.google.com [209.85.166.51]) by imf22.hostedemail.com (Postfix) with ESMTP for ; Fri, 20 Mar 2020 09:19:58 +0000 (UTC) Received: by mail-io1-f51.google.com with SMTP id n21so5188165ioo.10 for ; Fri, 20 Mar 2020 02:19:58 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=uJsVOgGPqb/q2iRd8gn1ZD5qGfpeyHF3Le1yJsRuXmA=; b=P40kBnaTd399NxpP8B3CDrW2EqNichDXtrwhLFk1eoZSf2Xyn5OM0CPypIcVOaDqSp +x1x31mXzMGtZkwDScNBn5nCcLTPCQJSRzy6q3EedUh6RzFglQmEhIH2jqqL60HGKPih /o6GdHksAfcosoZUgZo9fMBLQTmQECxCj8ZeJbLpSk+YHw4SR3PPewjR0BQKJjLVyRE1 SlPBPoJwZmRSWyEZXQ1AuClL3fFUywRZRG9K+ZzgMMkLhJq29ZnrTcnnUCq7HZyQR2dA 4acUhas9LpD3+GvA+Qlq1yXuoug0IYoGmlbiTIPu2C6nuXHPXDyem9mBZS7LP2+GydiM r/iA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=uJsVOgGPqb/q2iRd8gn1ZD5qGfpeyHF3Le1yJsRuXmA=; b=aFFuRpK5wl77oaiIpq8bNzwyxBC3EQcASOgWd5oovS9WoGex/sVhXDsXJC2Up/dkDQ K35YXxibPr/kHJm/oq4AO3znsSASXQcmYY77Jwonsuat/fey+GrtWBBHS2BWM6Q1Sj0s +RlFaSalj+rj84n/BLqxkA25Xh4lRnPLrVZuPNmOt9fS146QstC4Hu/OU275DMQmyNB3 JkKkGHxcIvHHutOLSo4mFqt663Bl77HQUAxQGo/qdWutFfz1zglZGs2MHqCUO0ACUxkp DQeYQ82Lkr01ljZVf0meZK5y+oKOCqmIyWAj4T+VjZymymYTa+dKUHAmdJCq7V0XtfQn KEdg== X-Gm-Message-State: ANhLgQ1i+Tc9aSAFpLkkp3/wxBOzmNxM2VRUkewD4utif+l2WwPkePGY WGS33KTJq5e4C2zyMJkOy0DKCKaA1mTNQWAsaA== X-Google-Smtp-Source: ADFU+vvxzskkGRY542ktgfC4s1OwlBZVf3HnaW3+tx6X2uncrz/ptEmG7mjDOPJc15oL/YXIk+UmZhf/l6iqeWNK+z4= X-Received: by 2002:a5e:d512:: with SMTP id e18mr6593451iom.209.1584695997679; Fri, 20 Mar 2020 02:19:57 -0700 (PDT) MIME-Version: 1.0 References: <1584333244-10480-3-git-send-email-kernelfans@gmail.com> <1584445652-30064-1-git-send-email-kernelfans@gmail.com> In-Reply-To: From: Pingfan Liu Date: Fri, 20 Mar 2020 17:19:46 +0800 Message-ID: Subject: Re: [PATCHv7 2/3] mm/gup: fix omission of check on FOLL_LONGTERM in gup fast path To: John Hubbard Cc: Linux-MM , Ira Weiny , Andrew Morton , Mike Rapoport , Dan Williams , Matthew Wilcox , "Aneesh Kumar K.V" , Christoph Hellwig , Shuah Khan , Jason Gunthorpe , LKML Content-Type: text/plain; charset="UTF-8" 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 Fri, Mar 20, 2020 at 6:17 AM John Hubbard wrote: > > On 3/17/20 4:47 AM, Pingfan Liu wrote: > > FOLL_LONGTERM is a special case of FOLL_PIN. It suggests a pin which is > > going to be given to hardware and can't move. It would truncate CMA > > permanently and should be excluded. > > > > In gup slow path, slow path, where > > > s/slow path, slow path/slow path/ Yeah. [...] > > > > /* > > + * Huge page's subpages have the same migrate type due to either > > + * allocation from a free_list[] or alloc_contig_range() with > > + * param MIGRATE_MOVABLE. So it is enough to check on a subpage. > > + */ > > Urggh, this comment is fine in the commit description, but at this location in the > code it is completely incomprehensible! Instead of an extremely far-removed tidbit about > interactions between CMA and huge pages, this comment should be explaining why we bail > out early in the specific case of FOLL_PIN + FOLL_LONGTERM. And we don't bail out for > FOLL_GET + FOLL_LONGTERM... > > > I'm expect it is something like: > > /* > * We can't do FOLL_LONGTERM + FOLL_PIN with CMA in the gup fast > * path, so fail and let the caller fall back to the slow path. > */ > > > ...approximately. Right? Yes, right. And I think it is better to drop "We". Thanks, Pingfan