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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 DBF07C2BB1D for ; Wed, 15 Apr 2020 02:42:42 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 9F5582076C for ; Wed, 15 Apr 2020 02:42:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="J2Zg0lkj" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9F5582076C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=nvidia.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 383838E0006; Tue, 14 Apr 2020 22:42:42 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 334468E0001; Tue, 14 Apr 2020 22:42:42 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 24A638E0006; Tue, 14 Apr 2020 22:42:42 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0231.hostedemail.com [216.40.44.231]) by kanga.kvack.org (Postfix) with ESMTP id 0B4358E0001 for ; Tue, 14 Apr 2020 22:42:42 -0400 (EDT) Received: from smtpin30.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id BD44B181AC9B6 for ; Wed, 15 Apr 2020 02:42:41 +0000 (UTC) X-FDA: 76708541322.30.road18_51aead9f3fb0b X-HE-Tag: road18_51aead9f3fb0b X-Filterd-Recvd-Size: 4235 Received: from hqnvemgate24.nvidia.com (hqnvemgate24.nvidia.com [216.228.121.143]) by imf39.hostedemail.com (Postfix) with ESMTP for ; Wed, 15 Apr 2020 02:42:41 +0000 (UTC) Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate24.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Tue, 14 Apr 2020 19:40:50 -0700 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate101.nvidia.com (PGP Universal service); Tue, 14 Apr 2020 19:42:39 -0700 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Tue, 14 Apr 2020 19:42:39 -0700 Received: from DRHQMAIL107.nvidia.com (10.27.9.16) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Wed, 15 Apr 2020 02:42:39 +0000 Received: from [10.2.85.126] (10.124.1.5) by DRHQMAIL107.nvidia.com (10.27.9.16) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Wed, 15 Apr 2020 02:42:38 +0000 Subject: Re: [PATCHv3, RESEND 5/8] khugepaged: Allow to collapse a page shared across fork To: "Kirill A. Shutemov" CC: "Kirill A. Shutemov" , , Andrea Arcangeli , Zi Yan , Yang Shi , Ralph Campbell , William Kucharski , , References: <20200413125220.663-1-kirill.shutemov@linux.intel.com> <20200413125220.663-6-kirill.shutemov@linux.intel.com> <0efcc512-6f12-1ff0-9885-871172fac766@nvidia.com> <20200414213526.ecn3zcgnqxoveddq@box> X-Nvconfidentiality: public From: John Hubbard Message-ID: Date: Tue, 14 Apr 2020 19:42:39 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: <20200414213526.ecn3zcgnqxoveddq@box> X-Originating-IP: [10.124.1.5] X-ClientProxiedBy: HQMAIL101.nvidia.com (172.20.187.10) To DRHQMAIL107.nvidia.com (10.27.9.16) Content-Type: text/plain; charset="utf-8"; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=nvidia.com; s=n1; t=1586918450; bh=qTZY0os6at1npMB2sob6j3xFufXnjCkxklf/oSH4Ng4=; h=X-PGP-Universal:Subject:To:CC:References:X-Nvconfidentiality:From: Message-ID:Date:User-Agent:MIME-Version:In-Reply-To: X-Originating-IP:X-ClientProxiedBy:Content-Type:Content-Language: Content-Transfer-Encoding; b=J2Zg0lkjZUPsttHoKMtn9tpNoDDxi1U92V00cmqjG/PpxSoMtE8eYf5XO9sNHBsIH 6vglRMiJNVizuNVNNZL0AtGHFIcJFipXPZUBBZwi4LRD3eKXA9N2yWohAOvv9UHJuU QkwyRj9HHf5/iqlqbeHn5+DqAcE4CfpiQ7ojVy/uqe6JK1SqCdozN+XF0LWEFKfflW QYUyE4JNZOM70r5B+RJ6/zX/pn+8XHydqN6N79BrwBljvsYKWrkJ1YXnckWE57evIT mtQiI0DdUGUJ38Ftrf1dM/iMTNd8FjvOwTkRJdu+Jei7quFJl9cW7iJGsjTM0B7xoj RyByOosLIt8sQ== 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 2020-04-14 14:35, Kirill A. Shutemov wrote: > 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. > Yes, you are right. I misread the condition. This actually is just right. :) thanks, -- John Hubbard NVIDIA