From nobody Thu Sep 18 08:31:26 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 8CE8CC4167B for ; Thu, 8 Dec 2022 18:03:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229650AbiLHSDZ (ORCPT ); Thu, 8 Dec 2022 13:03:25 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59622 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229894AbiLHSDT (ORCPT ); Thu, 8 Dec 2022 13:03:19 -0500 Received: from mail-pj1-x102d.google.com (mail-pj1-x102d.google.com [IPv6:2607:f8b0:4864:20::102d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 57D0D5BD60 for ; Thu, 8 Dec 2022 10:03:16 -0800 (PST) Received: by mail-pj1-x102d.google.com with SMTP id o12so2306871pjo.4 for ; Thu, 08 Dec 2022 10:03:16 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=content-transfer-encoding:mime-version:reply-to:references :in-reply-to:message-id:date:subject:cc:to:from:from:to:cc:subject :date:message-id:reply-to; bh=E96Wm/nE/BO1oqx7KrRbQksoP0SM8QfWpUYCtfF7ZOY=; b=elKCQdyBJ0zfJyNZL9MWCMZLH4HbJp0sc16DHkwY2E5BuxBXc6+kjPqmOH0MEON8c+ x1q8YZAV5N61RQT/m3OutBjmiEN7IieOIDAJHd/hq9flNutIgFBfrmAvkwCHiWZpU968 l3IuT9uaAPkuHG77zs7QLsSUC6ld+XhS8pJMfNyXq93eNDv1gMb8XaRWqLbPCQg4FLds Zw5LVsx1I3Bf87bQVz8e4Azxrug7PBuZkoHYH/SIAcF3bH6ttLQh+TrjPhbCygJXcrfP dhI88Wq2hZmQ5pkdV4izpmRYDsPTRa9HKcydpMuA1M6ve9u4TicYtF5kp0e90xqzNGBJ sKCw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=content-transfer-encoding:mime-version:reply-to:references :in-reply-to:message-id:date:subject:cc:to:from:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=E96Wm/nE/BO1oqx7KrRbQksoP0SM8QfWpUYCtfF7ZOY=; b=4w8ywLpr/2ueM0D5+aEjz0b4IF03Y2zZ3ofn/dDlUpb5x1JiUyQHliVmlynL7GRONq GFuRvYC2zlp+8IRnksjUOzgl0FhzSYNEW8jbQT/zfAc4GpNdLDocHXFLZYH2x2RQJ6gG YKe07sATnwSo2xLYug9D1QHtI8gPRf6V3pr7NCdrii3pd8dunhM3KTEwItVtobHWPwOj aNsTeEhkXxwXv7WV3arupWlm0bj+ir/pwDkfOlONDyjKk+sBiepw8lXv/6ZPvW/w8YNB fxvgsh7Ccwnv7RNalfDSWwMNu+XfFvGYPQQdlRpJ3E03BNqi7eLNs/+SkiOvrqLZ5keV izzw== X-Gm-Message-State: ANoB5pmOKyGH2sf0GlR8NjCjW3NuTYAe83iqkT5vPJV0Bt7qAjC+g7zn 0WSCQG8vxNSM0U/ZPyzR7lw= X-Google-Smtp-Source: AA0mqf4pM+kGOAZ0I0/E4epPe+dakTrALDjT5h+cTK/rmfAO6gWi5Nw7yw9MBJ7OdK2iYJAqFCaERA== X-Received: by 2002:a17:902:d58a:b0:189:a11e:9995 with SMTP id k10-20020a170902d58a00b00189a11e9995mr3153672plh.13.1670522595747; Thu, 08 Dec 2022 10:03:15 -0800 (PST) Received: from localhost.localdomain ([198.13.51.166]) by smtp.gmail.com with ESMTPSA id x23-20020a63db57000000b004785e505bcdsm13377909pgi.51.2022.12.08.10.03.10 (version=TLS1_3 cipher=TLS_CHACHA20_POLY1305_SHA256 bits=256/256); Thu, 08 Dec 2022 10:03:15 -0800 (PST) From: Kairui Song To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Andrew Morton , Miaohe Lin , David Hildenbrand , "Huang, Ying" , Hugh Dickins , Kairui Song Subject: [PATCH 1/5] swapfile: get rid of volatile and avoid redundant read Date: Fri, 9 Dec 2022 02:02:05 +0800 Message-Id: <20221208180209.50845-2-ryncsn@gmail.com> X-Mailer: git-send-email 2.35.2 In-Reply-To: <20221208180209.50845-1-ryncsn@gmail.com> References: <20221208180209.50845-1-ryncsn@gmail.com> Reply-To: Kairui Song MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Kairui Song Convert a volatile variable to more readable READ_ONCE. And this actually avoids the code from reading the variable twice redundantly when it races. Signed-off-by: Kairui Song Reviewed-by: "Huang, Ying" --- mm/swapfile.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/mm/swapfile.c b/mm/swapfile.c index 72e481aacd5d..ff4f3cb85232 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -1836,13 +1836,13 @@ static int unuse_pte_range(struct vm_area_struct *v= ma, pmd_t *pmd, pte_t *pte; struct swap_info_struct *si; int ret =3D 0; - volatile unsigned char *swap_map; =20 si =3D swap_info[type]; pte =3D pte_offset_map(pmd, addr); do { struct folio *folio; unsigned long offset; + unsigned char swp_count; =20 if (!is_swap_pte(*pte)) continue; @@ -1853,7 +1853,6 @@ static int unuse_pte_range(struct vm_area_struct *vma= , pmd_t *pmd, =20 offset =3D swp_offset(entry); pte_unmap(pte); - swap_map =3D &si->swap_map[offset]; folio =3D swap_cache_get_folio(entry, vma, addr); if (!folio) { struct page *page; @@ -1870,8 +1869,10 @@ static int unuse_pte_range(struct vm_area_struct *vm= a, pmd_t *pmd, folio =3D page_folio(page); } if (!folio) { - if (*swap_map =3D=3D 0 || *swap_map =3D=3D SWAP_MAP_BAD) + swp_count =3D READ_ONCE(si->swap_map[offset]); + if (swp_count =3D=3D 0 || swp_count =3D=3D SWAP_MAP_BAD) goto try_next; + return -ENOMEM; } =20 --=20 2.35.2