From patchwork Fri Jun 9 08:15:18 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Qi Zheng X-Patchwork-Id: 13273413 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 684C7C7EE25 for ; Fri, 9 Jun 2023 08:19:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240462AbjFIITJ (ORCPT ); Fri, 9 Jun 2023 04:19:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52008 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238959AbjFIISY (ORCPT ); Fri, 9 Jun 2023 04:18:24 -0400 Received: from out-14.mta0.migadu.com (out-14.mta0.migadu.com [IPv6:2001:41d0:1004:224b::e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A03722121 for ; Fri, 9 Jun 2023 01:17:37 -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=1686298655; 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=EMn+msnIJXvC+06grZ542lhB8pLG9zNhZSiyiHhRbaA=; b=QnAzENdGYWeYO57Spgjhk1adZxJY7gan2t4wYWPeZIaItdmJZDM8xOICqPyq/QELcJD9OY hG30tKtjBO4CWu/+8SDMmqFoQybaFEZQceY8dbZCLKigPc6SX9awgQJwPEusZAlihLEw5W Hw8FqnopH5nBR0yG+Weoe/3z4ob2VOY= 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 7/7] Revert "mm: vmscan: make global slab shrink lockless" Date: Fri, 9 Jun 2023 08:15:18 +0000 Message-Id: <20230609081518.3039120-8-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 f95bdb700bc6bb74e1199b1f5f90c613e152cfa7. 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. After discussion, 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 | 28 ++++++++++++++++------------ 1 file changed, 16 insertions(+), 12 deletions(-) diff --git a/mm/vmscan.c b/mm/vmscan.c index a008d7f2d0fc..5bf98d0a22c9 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -57,7 +57,6 @@ #include #include #include -#include #include #include @@ -191,7 +190,6 @@ int vm_swappiness = 60; LIST_HEAD(shrinker_list); DECLARE_RWSEM(shrinker_rwsem); -DEFINE_SRCU(shrinker_srcu); #ifdef CONFIG_MEMCG static int shrinker_nr_max; @@ -742,7 +740,7 @@ void free_prealloced_shrinker(struct shrinker *shrinker) void register_shrinker_prepared(struct shrinker *shrinker) { down_write(&shrinker_rwsem); - list_add_tail_rcu(&shrinker->list, &shrinker_list); + list_add_tail(&shrinker->list, &shrinker_list); shrinker->flags |= SHRINKER_REGISTERED; shrinker_debugfs_add(shrinker); up_write(&shrinker_rwsem); @@ -797,15 +795,13 @@ void unregister_shrinker(struct shrinker *shrinker) return; down_write(&shrinker_rwsem); - list_del_rcu(&shrinker->list); + list_del(&shrinker->list); shrinker->flags &= ~SHRINKER_REGISTERED; if (shrinker->flags & SHRINKER_MEMCG_AWARE) unregister_memcg_shrinker(shrinker); debugfs_entry = shrinker_debugfs_detach(shrinker, &debugfs_id); up_write(&shrinker_rwsem); - synchronize_srcu(&shrinker_srcu); - shrinker_debugfs_remove(debugfs_entry, debugfs_id); kfree(shrinker->nr_deferred); @@ -825,7 +821,6 @@ void synchronize_shrinkers(void) { down_write(&shrinker_rwsem); up_write(&shrinker_rwsem); - synchronize_srcu(&shrinker_srcu); } EXPORT_SYMBOL(synchronize_shrinkers); @@ -1036,7 +1031,6 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, { unsigned long ret, freed = 0; struct shrinker *shrinker; - int srcu_idx; /* * The root memcg might be allocated even though memcg is disabled @@ -1048,10 +1042,10 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, if (!mem_cgroup_disabled() && !mem_cgroup_is_root(memcg)) return shrink_slab_memcg(gfp_mask, nid, memcg, priority); - srcu_idx = srcu_read_lock(&shrinker_srcu); + if (!down_read_trylock(&shrinker_rwsem)) + goto out; - list_for_each_entry_srcu(shrinker, &shrinker_list, list, - srcu_read_lock_held(&shrinker_srcu)) { + list_for_each_entry(shrinker, &shrinker_list, list) { struct shrink_control sc = { .gfp_mask = gfp_mask, .nid = nid, @@ -1062,9 +1056,19 @@ static unsigned long shrink_slab(gfp_t gfp_mask, int nid, if (ret == SHRINK_EMPTY) ret = 0; freed += ret; + /* + * Bail out if someone want to register a new shrinker to + * prevent the registration from being stalled for long periods + * by parallel ongoing shrinking. + */ + if (rwsem_is_contended(&shrinker_rwsem)) { + freed = freed ? : 1; + break; + } } - srcu_read_unlock(&shrinker_srcu, srcu_idx); + up_read(&shrinker_rwsem); +out: cond_resched(); return freed; }