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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, UNPARSEABLE_RELAY,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham 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 EA1D0C2BA2B for ; Wed, 15 Apr 2020 20:39:27 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id AAA5420768 for ; Wed, 15 Apr 2020 20:39:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org AAA5420768 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 5B2968E0046; Wed, 15 Apr 2020 16:39:27 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 562798E0001; Wed, 15 Apr 2020 16:39:27 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 49F0E8E0046; Wed, 15 Apr 2020 16:39:27 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0232.hostedemail.com [216.40.44.232]) by kanga.kvack.org (Postfix) with ESMTP id 2E1448E0001 for ; Wed, 15 Apr 2020 16:39:27 -0400 (EDT) Received: from smtpin06.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id E938B62DD for ; Wed, 15 Apr 2020 20:39:26 +0000 (UTC) X-FDA: 76711254732.06.fan21_182cb71a6c501 X-HE-Tag: fan21_182cb71a6c501 X-Filterd-Recvd-Size: 5184 Received: from out30-133.freemail.mail.aliyun.com (out30-133.freemail.mail.aliyun.com [115.124.30.133]) by imf30.hostedemail.com (Postfix) with ESMTP for ; Wed, 15 Apr 2020 20:39:25 +0000 (UTC) X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R201e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07488;MF=yang.shi@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0TvduEle_1586983159; Received: from US-143344MP.local(mailfrom:yang.shi@linux.alibaba.com fp:SMTPD_---0TvduEle_1586983159) by smtp.aliyun-inc.com(127.0.0.1); Thu, 16 Apr 2020 04:39:21 +0800 Subject: Re: [PATCHv3, RESEND 5/8] khugepaged: Allow to collapse a page shared across fork To: "Kirill A. Shutemov" , akpm@linux-foundation.org, Andrea Arcangeli Cc: Zi Yan , Ralph Campbell , John Hubbard , William Kucharski , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20200413125220.663-1-kirill.shutemov@linux.intel.com> <20200413125220.663-6-kirill.shutemov@linux.intel.com> From: Yang Shi Message-ID: Date: Wed, 15 Apr 2020 13:39:16 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.12; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20200413125220.663-6-kirill.shutemov@linux.intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US 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 4/13/20 5:52 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). > > Logic to check the refcound is moved to a separate function. s/refcound/refcount > Note that the function is ready to deal with compound pages. It's > preparation for the following patch. > > VM_BUG_ON_PAGE() was removed from __collapse_huge_page_copy() as the > invariant it checks is no longer valid: the source can be mapped > multiple times now. > > Signed-off-by: Kirill A. Shutemov > --- > mm/khugepaged.c | 41 ++++++++++++++++++++++++++++++----------- > 1 file changed, 30 insertions(+), 11 deletions(-) Just a minor typo problem. Acked-by: Yang Shi > > diff --git a/mm/khugepaged.c b/mm/khugepaged.c > index e3e41c2768d8..f9864644c3b7 100644 > --- a/mm/khugepaged.c > +++ b/mm/khugepaged.c > @@ -529,6 +529,24 @@ static void release_pte_pages(pte_t *pte, pte_t *_pte) > } > } > > +static bool is_refcount_suitable(struct page *page) > +{ > + int expected_refcount, refcount; > + > + refcount = page_count(page); > + expected_refcount = total_mapcount(page); > + if (PageSwapCache(page)) > + expected_refcount += compound_nr(page); > + > + 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"); > + } > + > + return page_count(page) == expected_refcount; > +} > + > static int __collapse_huge_page_isolate(struct vm_area_struct *vma, > unsigned long address, > pte_t *pte) > @@ -581,11 +599,17 @@ 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 > + * an additinal pin on the page. > + * > + * 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 (!is_refcount_suitable(page)) { > unlock_page(page); > result = SCAN_PAGE_COUNT; > goto out; > @@ -672,7 +696,6 @@ 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 > @@ -1201,12 +1224,8 @@ 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 (!is_refcount_suitable(page)) { > result = SCAN_PAGE_COUNT; > goto out_unmap; > }