From nobody Wed Dec 17 19:02:48 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id C31B3C61D9B for ; Wed, 22 Nov 2023 14:01:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344277AbjKVOBI (ORCPT ); Wed, 22 Nov 2023 09:01:08 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32920 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343965AbjKVOBG (ORCPT ); Wed, 22 Nov 2023 09:01:06 -0500 Received: from szxga03-in.huawei.com (szxga03-in.huawei.com [45.249.212.189]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 291B5A9 for ; Wed, 22 Nov 2023 06:01:01 -0800 (PST) Received: from kwepemm000020.china.huawei.com (unknown [172.30.72.57]) by szxga03-in.huawei.com (SkyGuard) with ESMTP id 4Sb2pS07YNzMnLj; Wed, 22 Nov 2023 21:56:15 +0800 (CST) Received: from localhost.localdomain (10.175.112.125) by kwepemm000020.china.huawei.com (7.193.23.93) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.35; Wed, 22 Nov 2023 22:00:58 +0800 From: Peng Zhang To: , CC: , , , , , , , , , , ZhangPeng Subject: [RFC PATCH] mm: filemap: avoid unnecessary major faults in filemap_fault() Date: Wed, 22 Nov 2023 22:00:52 +0800 Message-ID: <20231122140052.4092083-1-zhangpeng362@huawei.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Originating-IP: [10.175.112.125] X-ClientProxiedBy: dggems706-chm.china.huawei.com (10.3.19.183) To kwepemm000020.china.huawei.com (7.193.23.93) X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: ZhangPeng The major fault occurred when using mlockall(MCL_CURRENT | MCL_FUTURE) in application, which leading to an unexpected performance issue[1]. This caused by temporarily cleared pte during a read/modify/write update of the pte, eg, do_numa_page()/change_pte_range(). For the data segment of the user-mode program, the global variable area is a private mapping. After the pagecache is loaded, the private anonymous page is generated after the COW is triggered. Mlockall can lock COW pages (anonymous pages), but the original file pages cannot be locked and may be reclaimed. If the global variable (private anon page) is accessed when vmf->pte is zeroed in numa fault, a file page fault will be triggered. At this time, the original private file page may have been reclaimed. If the page cache is not available at this time, a major fault will be triggered and the file will be read, causing additional overhead. Fix this by rechecking the pte by holding ptl in filemap_fault() before triggering a major fault. [1] https://lore.kernel.org/linux-mm/9e62fd9a-bee0-52bf-50a7-498fa17434ee@h= uawei.com/ Signed-off-by: ZhangPeng Signed-off-by: Kefeng Wang Reviewed-by: Yin Fengwei Suggested-by: "Huang, Ying" --- mm/filemap.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/mm/filemap.c b/mm/filemap.c index 71f00539ac00..bb5e6a2790dc 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -3226,6 +3226,20 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) mapping_locked =3D true; } } else { + pte_t *ptep =3D pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd, + vmf->address, &vmf->ptl); + if (ptep) { + /* + * Recheck pte with ptl locked as the pte can be cleared + * temporarily during a read/modify/write update. + */ + if (unlikely(!pte_none(ptep_get(ptep)))) + ret =3D VM_FAULT_NOPAGE; + pte_unmap_unlock(ptep, vmf->ptl); + if (unlikely(ret)) + return ret; + } + /* No page in the page cache at all */ count_vm_event(PGMAJFAULT); count_memcg_event_mm(vmf->vma->vm_mm, PGMAJFAULT); --=20 2.25.1