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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 15DA5C001DE for ; Mon, 19 Jun 2023 20:20:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229570AbjFSUU0 (ORCPT ); Mon, 19 Jun 2023 16:20:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33514 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230020AbjFSUUV (ORCPT ); Mon, 19 Jun 2023 16:20:21 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3528DE7E for ; Mon, 19 Jun 2023 13:20:17 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 144FB60EB0 for ; Mon, 19 Jun 2023 20:20:17 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6C19BC433C8; Mon, 19 Jun 2023 20:20:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1687206016; bh=/icd64qkLbqreKJd3BuDyH2okX0wHugcTzM+I54Va2E=; h=Date:To:From:Subject:From; b=EerlLHu7OY9NXuElwIZYEEVkTN1TGdrrITnS79LmZFnGhnIMq1Sh7ThStUKsDT2cO W9M+yGyMQenm7sZDT6y9jmnVlZ0PmyfIriAKaS7GDNibveUMS/l0aCyVvJP9OWlc8x ODpf58BSVaiYrU5fpA/fHnGgquN2RrDc4noK6WZ8= Date: Mon, 19 Jun 2023 13:20:15 -0700 To: mm-commits@vger.kernel.org, yujie.liu@intel.com, vbabka@suse.cz, tkhai@ya.ru, roman.gushchin@linux.dev, muchun.song@linux.dev, david@fromorbit.com, zhengqi.arch@bytedance.com, akpm@linux-foundation.org From: Andrew Morton Subject: [merged mm-hotfixes-stable] revert-mm-vmscan-remove-shrinker_rwsem-from-synchronize_shrinkers.patch removed from -mm tree Message-Id: <20230619202016.6C19BC433C8@smtp.kernel.org> Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org The quilt patch titled Subject: Revert "mm: vmscan: remove shrinker_rwsem from synchronize_shrinkers()" has been removed from the -mm tree. Its filename was revert-mm-vmscan-remove-shrinker_rwsem-from-synchronize_shrinkers.patch This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm ------------------------------------------------------ From: Qi Zheng Subject: Revert "mm: vmscan: remove shrinker_rwsem from synchronize_shrinkers()" Date: Fri, 9 Jun 2023 08:15:13 +0000 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/ Link: https://lkml.kernel.org/r/20230609081518.3039120-3-qi.zheng@linux.dev Reported-by: kernel test robot Closes: https://lore.kernel.org/oe-lkp/202305230837.db2c233f-yujie.liu@intel.com Signed-off-by: Qi Zheng Cc: Dave Chinner Cc: Kirill Tkhai Cc: Muchun Song Cc: Roman Gushchin Cc: Vlastimil Babka Signed-off-by: Andrew Morton --- mm/vmscan.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) --- a/mm/vmscan.c~revert-mm-vmscan-remove-shrinker_rwsem-from-synchronize_shrinkers +++ a/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); } _ Patches currently in -mm which might be from zhengqi.arch@bytedance.com are