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: 13273416 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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id DEF5AC7EE2E for ; Fri, 9 Jun 2023 08:17:11 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 797788E000B; Fri, 9 Jun 2023 04:17:11 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 721078E0003; Fri, 9 Jun 2023 04:17:11 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5C23B8E000B; Fri, 9 Jun 2023 04:17:11 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 481078E0003 for ; Fri, 9 Jun 2023 04:17:11 -0400 (EDT) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 19FF314013C for ; Fri, 9 Jun 2023 08:17:11 +0000 (UTC) X-FDA: 80882504262.14.7D01E26 Received: from out-58.mta0.migadu.com (out-58.mta0.migadu.com [91.218.175.58]) by imf30.hostedemail.com (Postfix) with ESMTP id 421EB80015 for ; Fri, 9 Jun 2023 08:17:09 +0000 (UTC) Authentication-Results: imf30.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=wuAhbqfY; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf30.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.58 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1686298629; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=h+9C3yhXhe+HsjvGtX6Jxz3ecYmnsu4DemmWgRFXfj8=; b=sy4foSZhKGBqlgVeHf+1yGa1w70GzwvF80dT3th7U5ZOl1dss3bh9CGs9cEtk4vx9pqZY0 +dGvowywQmgX5yYjMgWsO1Zg2sxk5sbAyStB2XwzA/VfwrY15z94ttWymMc961Xo0fb9G0 GMHK8RWJptQnhf3Y/f3QCjqGY0TWPfk= ARC-Authentication-Results: i=1; imf30.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=wuAhbqfY; dmarc=pass (policy=none) header.from=linux.dev; spf=pass (imf30.hostedemail.com: domain of qi.zheng@linux.dev designates 91.218.175.58 as permitted sender) smtp.mailfrom=qi.zheng@linux.dev ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1686298629; a=rsa-sha256; cv=none; b=VjCEEkJtklfF/1VLSkQpGnvRON8osgfpStt5PUl+1G6ELSCP8k8mpzQK3kKyGo374x2Im5 VASBWgKSsj89VwLjEfv6gGmk4JVpynLjS0pRz+7F/6qsLwknSYHjIV63VYPshR1ieHCLaT M56UmmwsWDYyfV0UXHkj+XmWTo0sQu4= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. 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-Rspamd-Queue-Id: 421EB80015 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: cgraope53uq8ck7119osa18kjmfqjdsb X-HE-Tag: 1686298629-885771 X-HE-Meta: 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 3iZA8PdJ R14XeSlEKPiYIjP9yUvy/ZL66csQxENpTAyt34DSfeHUACR3sNcyIcFTYFJoHPy45zKCjT16rhCPN/LfqcZvVesRGo+2z/viUEZTr3A6f5QI40QjD19P7Jxnq4pB5whzcTIdJ7gGePwO8HZ8tZ1xFGpNCoVfOzAoXr3QHQryTEt8xGP6BhjtbevmWKJhvkfMm2KLBUIVRK9v1dTDlZo+ikPzFSYmKPLcVttSpeFstUICSyqUaTkEQoskBE1usE8d+AdNlyttrv5VBvE4= 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: 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); }