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=-8.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 96D3CC2BA80 for ; Mon, 6 Apr 2020 20:15:43 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 65A8720753 for ; Mon, 6 Apr 2020 20:15:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=nvidia.com header.i=@nvidia.com header.b="jbJjCCKR" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 65A8720753 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 D5F208E0005; Mon, 6 Apr 2020 16:15:42 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id D0F368E0001; Mon, 6 Apr 2020 16:15:42 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C251E8E0005; Mon, 6 Apr 2020 16:15:42 -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 AC4EE8E0001 for ; Mon, 6 Apr 2020 16:15:42 -0400 (EDT) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with ESMTP id DC944180AD811 for ; Mon, 6 Apr 2020 20:15:41 +0000 (UTC) X-FDA: 76678535682.16.brick14_147ff28f47d3b X-HE-Tag: brick14_147ff28f47d3b X-Filterd-Recvd-Size: 5280 Received: from hqnvemgate26.nvidia.com (hqnvemgate26.nvidia.com [216.228.121.65]) by imf38.hostedemail.com (Postfix) with ESMTP for ; Mon, 6 Apr 2020 20:15:40 +0000 (UTC) Received: from hqpgpgate101.nvidia.com (Not Verified[216.228.121.13]) by hqnvemgate26.nvidia.com (using TLS: TLSv1.2, DES-CBC3-SHA) id ; Mon, 06 Apr 2020 13:15:26 -0700 Received: from hqmail.nvidia.com ([172.20.161.6]) by hqpgpgate101.nvidia.com (PGP Universal service); Mon, 06 Apr 2020 13:15:39 -0700 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Mon, 06 Apr 2020 13:15:39 -0700 Received: from DRHQMAIL107.nvidia.com (10.27.9.16) by HQMAIL111.nvidia.com (172.20.187.18) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Mon, 6 Apr 2020 20:15:39 +0000 Received: from rcampbell-dev.nvidia.com (10.124.1.5) by DRHQMAIL107.nvidia.com (10.27.9.16) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Mon, 6 Apr 2020 20:15:38 +0000 Subject: Re: [PATCHv2 5/8] khugepaged: Allow to callapse a page shared across fork To: "Kirill A. Shutemov" , , Andrea Arcangeli CC: Zi Yan , Yang Shi , , , "Kirill A. Shutemov" References: <20200403112928.19742-1-kirill.shutemov@linux.intel.com> <20200403112928.19742-6-kirill.shutemov@linux.intel.com> X-Nvconfidentiality: public From: Ralph Campbell Message-ID: Date: Mon, 6 Apr 2020 13:15:36 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.2 MIME-Version: 1.0 In-Reply-To: <20200403112928.19742-6-kirill.shutemov@linux.intel.com> 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=1586204126; bh=hFuW01LWHzr2dqJom6FxWQGnFY1OhyVXI3oYPFLQ59E=; 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=jbJjCCKR0rIwyP0jP9LUfP8gwmlKrlfhc+qy4ikTldzH//xZo1teBxU+QFeWnR3oC 5pxPEkak2rlSEedJR6NMijUevh0UjCpuv+vFIk/935VIKD/FQrQqP1dTvqIeV+gdun f1tx9nox2zGqZ7Zf1nOHkfGWilBqVgsSBErruMZNVjbqDKQAF6UICM80pf5gEUdn5E NMT7rq/neenzraOVssAHE3gn0eLU1NXkH0hjHj6o0jFtPgDEgs7SgOf4HzF7qKZ37E RUEUfdu/H1DrDjWE1qoTERXpvPbbldFVDzfqsA+9y+luj77wLIez1l2yXfbPWSeQxf jhgVbweO2CmfA== 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 4/3/20 4:29 AM, Kirill A. Shutemov wrote: > The page can be included into collapse as long as it doesn't have extra > pins (from GUP or otherwise). > > Signed-off-by: Kirill A. Shutemov > --- > mm/khugepaged.c | 25 ++++++++++++++----------- > 1 file changed, 14 insertions(+), 11 deletions(-) > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index 57ff287caf6b..1e7e6543ebca 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -581,11 +581,18 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > } > > /* > - * cannot use mapcount: can't collapse if there's a gup pin. > - * The page must only be referenced by the scanned process > - * and page swap cache. > + * Check if the page has any GUP (or other external) pins. > + * > + * The page table that maps the page has been already unlinked > + * from the page table tree and this process cannot get > + * additinal pin on the page. s/additinal/an additional > + * > + * New pins can come later if the page is shared across fork, > + * but not for the this process. It is fine. The other process > + * cannot write to the page, only trigger CoW. > */ > - if (page_count(page) != 1 + PageSwapCache(page)) { > + if (total_mapcount(page) + PageSwapCache(page) != > + page_count(page)) { > unlock_page(page); > result = SCAN_PAGE_COUNT; > goto out; > @@ -672,7 +679,6 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page, > } else { > src_page = pte_page(pteval); > copy_user_highpage(page, src_page, address, vma); > - VM_BUG_ON_PAGE(page_mapcount(src_page) != 1, src_page); > release_pte_page(src_page); > /* > * ptl mostly unnecessary, but preempt has to > @@ -1206,12 +1212,9 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, > goto out_unmap; > } > > - /* > - * cannot use mapcount: can't collapse if there's a gup pin. > - * The page must only be referenced by the scanned process > - * and page swap cache. > - */ > - if (page_count(page) != 1 + PageSwapCache(page)) { > + /* Check if the page has any GUP (or other external) pins */ > + if (total_mapcount(page) + PageSwapCache(page) != > + page_count(page)) { > result = SCAN_PAGE_COUNT; > goto out_unmap; > } >