From patchwork Fri Jun 9 08:15:16 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Qi Zheng X-Patchwork-Id: 13273411 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 24690C7EE2E for ; Fri, 9 Jun 2023 08:18:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240303AbjFIISz (ORCPT ); Fri, 9 Jun 2023 04:18:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51746 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240382AbjFIISI (ORCPT ); Fri, 9 Jun 2023 04:18:08 -0400 Received: from out-19.mta0.migadu.com (out-19.mta0.migadu.com [IPv6:2001:41d0:1004:224b::13]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 768AF211C for ; Fri, 9 Jun 2023 01:17:27 -0700 (PDT) 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=1686298645; 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=ptGmpfMk/kHVim/COA1N68hD8MGHSDZD7U0gMdC3pxY=; b=dUWb27UUXt+8QDbQIc9tustr3Ex0BabLxTJee5D+fXjeHZBQ4qcFjuXfmS9deSWg9pnPCR 9dTR+kP4JvZRsxWTBrikjSS0f2Fm0CUyHJiy5VG+bhRcgClpEyEjDlHhnKlTs1O4PWyCUu 6wpdq+dene7opH5wdk+agSCOHXRmYcg= 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 5/7] Revert "mm: vmscan: add shrinker_srcu_generation" Date: Fri, 9 Jun 2023 08:15:16 +0000 Message-Id: <20230609081518.3039120-6-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 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Qi Zheng This reverts commit 475733dda5aedba9e086379aafe6b5ffd53e8f5e. 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 revert the shrinker_srcu related changes first. [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 | 24 ++++-------------------- 1 file changed, 4 insertions(+), 20 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index d1d309fc3212..50775b73d0c7 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -192,7 +192,6 @@ int vm_swappiness = 60; LIST_HEAD(shrinker_list); DECLARE_RWSEM(shrinker_rwsem); DEFINE_SRCU(shrinker_srcu); -static atomic_t shrinker_srcu_generation = ATOMIC_INIT(0); #ifdef CONFIG_MEMCG static int shrinker_nr_max; @@ -818,7 +817,6 @@ void unregister_shrinker(struct shrinker *shrinker) debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id); up_write(&shrinker_rwsem); - atomic_inc(&shrinker_srcu_generation); synchronize_srcu(&shrinker_srcu); shrinker_debugfs_remove(debugfs_entry, debugfs_id); @@ -840,7 +838,6 @@ void synchronize_shrinkers(void) { down_write(&shrinker_rwsem); up_write(&shrinker_rwsem); - atomic_inc(&shrinker_srcu_generation); synchronize_srcu(&shrinker_srcu); } EXPORT_SYMBOL(synchronize_shrinkers); @@ -950,20 +947,18 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid, { struct shrinker_info *info; unsigned long ret, freed = 0; - int srcu_idx, generation; - int i = 0; + int srcu_idx; + int i; if (!mem_cgroup_online(memcg)) return 0; -again: srcu_idx = srcu_read_lock(&shrinker_srcu); info = shrinker_info_srcu(memcg, nid); if (unlikely(!info)) goto unlock; - generation = atomic_read(&shrinker_srcu_generation); - for_each_set_bit_from(i, info->map, info->map_nr_max) { + for_each_set_bit(i, info->map, info->map_nr_max) { struct shrink_control sc = { .gfp_mask = gfp_mask, .nid = nid, @@ -1009,11 +1004,6 @@ static unsigned long shrink_slab_memcg(gfp_t gfp_mask, int nid, set_shrinker_bit(memcg, nid, i); } freed += ret; - if (atomic_read(&shrinker_srcu_generation) != generation) { - srcu_read_unlock(&shrinker_srcu, srcu_idx); - i++; - goto again; - } } unlock: srcu_read_unlock(&shrinker_srcu, srcu_idx); @@ -1053,7 +1043,7 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, { unsigned long ret, freed = 0; struct shrinker *shrinker; - int srcu_idx, generation; + int srcu_idx; /* * The root memcg might be allocated even though memcg is disabled @@ -1067,7 +1057,6 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, srcu_idx = srcu_read_lock(&shrinker_srcu); - generation = atomic_read(&shrinker_srcu_generation); list_for_each_entry_srcu(shrinker, &shrinker_list, list, srcu_read_lock_held(&shrinker_srcu)) { struct shrink_control sc = { @@ -1080,11 +1069,6 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, if (ret == SHRINK_EMPTY) ret = 0; freed += ret; - - if (atomic_read(&shrinker_srcu_generation) != generation) { - freed = freed ? : 1; - break; - } } srcu_read_unlock(&shrinker_srcu, srcu_idx);