From patchwork Fri Jun 9 08:15:13 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Qi Zheng X-Patchwork-Id: 105379 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:a59:994d:0:b0:3d9:f83d:47d9 with SMTP id k13csp791167vqr; Fri, 9 Jun 2023 01:20:36 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ5XtIYjw2hlK1fe0jgWfDNboX5WYmezjkdoS+tAiYUaBRevG6m+TC2gsbdmhc46f1bP9f6i X-Received: by 2002:a05:6a00:1401:b0:661:4a00:1e8b with SMTP id l1-20020a056a00140100b006614a001e8bmr364256pfu.23.1686298836171; Fri, 09 Jun 2023 01:20:36 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1686298836; cv=none; d=google.com; s=arc-20160816; b=yYcfO9Ymdj+r5w5k9pJW5HOeiAEU7Ding3X0REKvOj+6xJPWpG+U5V5tXlnV9x/JE/ ZVjsqvKODhWCzKMatTSNc+pIcx3q/JYWs6HkCaWpn0MaQNw9WxbrnqaF8pd/nb/WUPEp Ueeksj/nN+8ZJBEA6+Ut67aunlJGHHj0TsojliCAoBOgBa1kqpUnUu+FKC7DwPc8zRq4 h7lxpbd8lpiTV/lyswqE56dJx8C+k2iqvfkQKP0qbkqwcSdLxyyA5O3L1ZvKUs0UVpju MRhouzL2PlIbk1r75GoJ3va/MlznXN48othlfjJueR8ekmZdVoZide/EZbbJSoQ9mtwc Ww9g== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:content-transfer-encoding:mime-version :references:in-reply-to:message-id:date:subject:cc:to:from :dkim-signature; bh=h+9C3yhXhe+HsjvGtX6Jxz3ecYmnsu4DemmWgRFXfj8=; b=haeA2FVPF102OIgqBkzdvpBrLNPkaQc/I6DnoEYxMTik6E03B7WpjDITw+pYbqYHHk mgt6TS/XARsDOLofi9HXw/V8ddWnvKh3NwmnbXs7ZcHCWMoJFNilnBESWA73M/IN9IVY tNJAj9MKvB2pSXhIYrPypVfb2KWfxYGh4ekEmqpuXACt8FS/KfsLVACtJUmYVdTCDbek PzI7lcskuyXAlYZLOZvQ4hhcjnNUorI2DlI1vIhy2EUmUkwJD3aBz6j3aKujOTatpiNe vV9C4W4HhGlLKHphskRlgnEnDc2F+Kw3fOwslKLlIAhiXOHXUSjGY8I0xa35hFQ0jG94 5ppw== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@linux.dev header.s=key1 header.b=wuAhbqfY; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linux.dev Received: from out1.vger.email (out1.vger.email. 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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1686298627; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=h+9C3yhXhe+HsjvGtX6Jxz3ecYmnsu4DemmWgRFXfj8=; b=wuAhbqfYpfLg4xQIqqPuVD2Rfwpmfb6tYYJSrXiOZnhHIakZm73KLHKdJ6ypEmmwJn/sYE EYRhoFMKrGVqbr6Pte8aRyp7U9WXdtvlr2I/JW1Y/9T0TEaerWHAcw46nLvdes6f6TOMB6 jHd4kdRFfCPCSHABsGW0lzVmG/1Xkxw= From: Qi Zheng To: akpm@linux-foundation.org Cc: david@fromorbit.com, tkhai@ya.ru, roman.gushchin@linux.dev, vbabka@suse.cz, muchun.song@linux.dev, yujie.liu@intel.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Qi Zheng Subject: [PATCH 2/7] Revert "mm: vmscan: remove shrinker_rwsem from synchronize_shrinkers()" Date: Fri, 9 Jun 2023 08:15:13 +0000 Message-Id: <20230609081518.3039120-3-qi.zheng@linux.dev> In-Reply-To: <20230609081518.3039120-1-qi.zheng@linux.dev> References: <20230609081518.3039120-1-qi.zheng@linux.dev> MIME-Version: 1.0 X-Migadu-Flow: FLOW_OUT X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,SPF_HELO_NONE,SPF_PASS, T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1768212488288814832?= X-GMAIL-MSGID: =?utf-8?q?1768212488288814832?= From: Qi Zheng This reverts commit 1643db98d9b314e0a592d152603094fbf7ab906e. Kernel test robot reports -88.8% regression in stress-ng.ramfs.ops_per_sec test case [1], which is caused by commit f95bdb700bc6 ("mm: vmscan: make global slab shrink lockless"). The root cause is that SRCU has to be careful to not frequently check for SRCU read-side critical section exits. Therefore, even if no one is currently in the SRCU read-side critical section, synchronize_srcu() cannot return quickly. That's why unregister_shrinker() has become slower. We will try to use the refcount+RCU method [2] proposed by Dave Chinner to continue to re-implement the lockless slab shrink. So we still need shrinker_rwsem in synchronize_shrinkers() after reverting the shrinker_srcu related changes. [1]. https://lore.kernel.org/lkml/202305230837.db2c233f-yujie.liu@intel.com/ [2]. https://lore.kernel.org/lkml/ZIJhou1d55d4H1s0@dread.disaster.area/ Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-lkp/202305230837.db2c233f-yujie.liu@intel.com Signed-off-by: Qi Zheng --- mm/vmscan.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index 4730dba253c8..0ba0e1180f3f 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -831,11 +831,15 @@ EXPORT_SYMBOL(unregister_shrinker); /** * synchronize_shrinkers - Wait for all running shrinkers to complete. * - * This is useful to guarantee that all shrinker invocations have seen an - * update, before freeing memory. + * This is equivalent to calling unregister_shrink() and register_shrinker(), + * but atomically and with less overhead. This is useful to guarantee that all + * shrinker invocations have seen an update, before freeing memory, similar to + * rcu. */ void synchronize_shrinkers(void) { + down_write(&shrinker_rwsem); + up_write(&shrinker_rwsem); atomic_inc(&shrinker_srcu_generation); synchronize_srcu(&shrinker_srcu); }