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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 BCA3FC433F5 for ; Wed, 22 Sep 2021 15:28:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 95A48611CA for ; Wed, 22 Sep 2021 15:28:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236433AbhIVPaJ (ORCPT ); Wed, 22 Sep 2021 11:30:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43360 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232318AbhIVPaI (ORCPT ); Wed, 22 Sep 2021 11:30:08 -0400 Received: from mail-pg1-x535.google.com (mail-pg1-x535.google.com [IPv6:2607:f8b0:4864:20::535]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 03D0AC061574 for ; Wed, 22 Sep 2021 08:28:38 -0700 (PDT) Received: by mail-pg1-x535.google.com with SMTP id m21so2999095pgu.13 for ; Wed, 22 Sep 2021 08:28:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=kp0DKxYvjStU9lLWJtLQliS/mXlIIBkYQTnbdZfBCzE=; b=D5TUqu83Rbx8goxjtEUmUrqUWsvsTOIx2eW7pCLs3HhFTKoq8sjupa1Mo/TqMWyPCM YBCATZaRsjXgWQjzPDoDN+e0qHNzLINwjO4LaDBqM+Vmug1fKMb43OsBMIwvq4t+9TY2 GE1l7w8qrpmu3fQCjV1A52r8N6XWz3BbE0Z1TN7neq12Z12RgAwQxyI6LFQVysYe2HvE aV99P+vNQqUfFkZ7DHvM7/nnhwW7ploLm7LP2ZHtHzmCZeYCwIYVXH2ZtV8X63Vkd0nP 1mqfyNEtpJ1grBCSkHFaGKY7VF3AOD/c6scYRq9u1h5++KbMz6bj9qGXd8KzKBgt18Xy b9iQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=kp0DKxYvjStU9lLWJtLQliS/mXlIIBkYQTnbdZfBCzE=; b=kzpsHs8MIwsYVJ+RM0wruUGDkCybC1AbOAcr0fKEkGkqPVi6Pmnr2ICPHn40amJe+m bEnQFM7Boz3T2OC7Xs4LEqvpZSBDmGZ41tIKr+XZ0C5o42238F5nGmf267ZXWN5KwaSB wIJ5DemGJ5mVW8jyhkVK4MnwTVqYG2JW8CNJCVmFQZT4Yp90aZIWyzlVr3FKfgtyNBbX AbT+6Mh+lnXFn24Pjh5rDGupjhihaVtRqCyXOrG4WfvEJ46i1KP+f6qPyhOQTW1Hz5+2 gOB+JttxK5Hk7ntOzMmrwYfjVQr809tN1/xVsmnlZj4r8w8MEJSTKV76gcYy79wXP7I4 dDVg== X-Gm-Message-State: AOAM532brAiAlyyh9OUVmvAd5OsQ324rzX9as3fLaYvV344eD/Yl7bN+ bkuYgcB93BQIqH9kbaLAddA= X-Google-Smtp-Source: ABdhPJwzBOGmnpoUbHW+VZBWNC4IQ7EVl0xzVd2oXnxyijuXxiB3uZqcUW9/9PFrZ1mrsGCdoxxwjA== X-Received: by 2002:a63:3d8c:: with SMTP id k134mr208828pga.394.1632324517574; Wed, 22 Sep 2021 08:28:37 -0700 (PDT) Received: from edumazet1.svl.corp.google.com ([2620:15c:2c4:201:9ca8:a7b7:b32f:a7fb]) by smtp.gmail.com with ESMTPSA id b17sm3178446pgl.61.2021.09.22.08.28.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Sep 2021 08:28:37 -0700 (PDT) From: Eric Dumazet To: Andrew Morton Cc: linux-kernel , linux-mm , Eric Dumazet , Eric Dumazet , Hugh Dickins Subject: [PATCH] mm: do not acquire zone lock in is_free_buddy_page() Date: Wed, 22 Sep 2021 08:28:33 -0700 Message-Id: <20210922152833.4023972-1-eric.dumazet@gmail.com> X-Mailer: git-send-email 2.33.0.464.g1972c5931b-goog MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Eric Dumazet Grabbing zone lock in is_free_buddy_page() gives a wrong sense of safety, and has potential performance implications when zone is experiencing lock contention. In any case, if a caller needs a stable result, it should grab zone lock before calling this function. Signed-off-by: Eric Dumazet Cc: Hugh Dickins --- mm/page_alloc.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index e115e21524739341d409b28379942241ed403060..cd8a72372b047e55c4cde80fe6b7a428d7721027 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -9354,21 +9354,21 @@ void __offline_isolated_pages(unsigned long start_pfn, unsigned long end_pfn) } #endif +/* + * This function returns a stable result only if called under zone lock. + */ bool is_free_buddy_page(struct page *page) { - struct zone *zone = page_zone(page); unsigned long pfn = page_to_pfn(page); - unsigned long flags; unsigned int order; - spin_lock_irqsave(&zone->lock, flags); for (order = 0; order < MAX_ORDER; order++) { struct page *page_head = page - (pfn & ((1 << order) - 1)); - if (PageBuddy(page_head) && buddy_order(page_head) >= order) + if (PageBuddy(page_head) && + buddy_order_unsafe(page_head) >= order) break; } - spin_unlock_irqrestore(&zone->lock, flags); return order < MAX_ORDER; } -- 2.33.0.464.g1972c5931b-goog