From patchwork Mon Apr 13 10:04:46 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Kirill A. Shutemov" X-Patchwork-Id: 11485395 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id D582E14DD for ; Mon, 13 Apr 2020 10:05:08 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id A2F1120786 for ; Mon, 13 Apr 2020 10:05:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A2F1120786 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id A0EB08E00FC; Mon, 13 Apr 2020 06:04:58 -0400 (EDT) Delivered-To: linux-mm-outgoing@kvack.org Received: by kanga.kvack.org (Postfix, from userid 40) id 997188E00FA; Mon, 13 Apr 2020 06:04:58 -0400 (EDT) X-Original-To: int-list-linux-mm@kvack.org X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 85E078E00FC; Mon, 13 Apr 2020 06:04:58 -0400 (EDT) X-Original-To: linux-mm@kvack.org X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0225.hostedemail.com [216.40.44.225]) by kanga.kvack.org (Postfix) with ESMTP id 699138E00FA for ; Mon, 13 Apr 2020 06:04:58 -0400 (EDT) Received: from smtpin19.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with ESMTP id 2EE712C06 for ; Mon, 13 Apr 2020 10:04:58 +0000 (UTC) X-FDA: 76702398276.19.steel90_2b4a897a3c632 X-Spam-Summary: 1,0,0,,d41d8cd98f00b204,kirill.shutemov@linux.intel.com,,RULES_HIT:30003:30054:30070,0,RBL:134.134.136.20:@linux.intel.com:.lbl8.mailshell.net-64.95.201.95 62.18.0.100,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:neutral,Custom_rules:0:0:0,LFtime:27,LUA_SUMMARY:none X-HE-Tag: steel90_2b4a897a3c632 X-Filterd-Recvd-Size: 5022 Received: from mga02.intel.com (mga02.intel.com [134.134.136.20]) by imf18.hostedemail.com (Postfix) with ESMTP for ; Mon, 13 Apr 2020 10:04:57 +0000 (UTC) IronPort-SDR: 0MdJGBlLZpEUywQxtw5TDhQKt3Q/7DKN7Sb+rpp/7tM0nRuFuGfcnafTGUORB6USlOhM2SfqJj ejAg993Qjp+A== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 13 Apr 2020 03:04:57 -0700 IronPort-SDR: cLZHmO+l+QKfmjoFjz3dZ1MGe5wuaWm/RPlyh8Ulv1B9c46mfYFCPsX0/iFhX7tTTOwgvuXTQ9 25V3V9bdAysQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,378,1580803200"; d="scan'208";a="426640509" Received: from black.fi.intel.com ([10.237.72.28]) by orsmga005.jf.intel.com with ESMTP; 13 Apr 2020 03:04:54 -0700 Received: by black.fi.intel.com (Postfix, from userid 1000) id A788B1F5; Mon, 13 Apr 2020 13:04:50 +0300 (EEST) From: "Kirill A. Shutemov" To: akpm@linux-foundation.org, Andrea Arcangeli Cc: Zi Yan , Yang Shi , Ralph Campbell , John Hubbard , William Kucharski , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" Subject: [PATCH 5/6] khugepaged: Allow to collapse a page shared across fork Date: Mon, 13 Apr 2020 13:04:46 +0300 Message-Id: <20200413100447.20073-6-kirill.shutemov@linux.intel.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200413100447.20073-1-kirill.shutemov@linux.intel.com> References: <20200413100447.20073-1-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 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: 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. 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 Reviewed-by: William Kucharski --- mm/khugepaged.c | 41 ++++++++++++++++++++++++++++++----------- 1 file changed, 30 insertions(+), 11 deletions(-) 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; }