From nobody Sun Feb 8 10:48:39 2026 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 37E9BC7EE25 for ; Fri, 9 Jun 2023 08:18:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240514AbjFIISf (ORCPT ); Fri, 9 Jun 2023 04:18:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51716 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240324AbjFIIRv (ORCPT ); Fri, 9 Jun 2023 04:17:51 -0400 Received: from out-21.mta0.migadu.com (out-21.mta0.migadu.com [91.218.175.21]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A94463AA4 for ; Fri, 9 Jun 2023 01:17:23 -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=1686298638; 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=fW5UuGuy06FRX8Px/N9YG/QTNF0coGlqdNSj4AuBaaM=; b=tddMOX9hrmBcUy1TaN6PYmjZr8N6htWv1AKIwBbCiMwwdMPB0GeJMYgG8Z8I93aOe/HBvd 5BXFnyv6bfT5hursOmsbSE208IL5wiQKL+bwZlti5+T99GzbUZ4tm7iuHx6iPsFe8QHCGt jtNfOoIRqSFtiW109WCZ6dTaNr7m36M= 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 4/7] Revert "mm: shrinkers: make count and scan in shrinker debugfs lockless" Date: Fri, 9 Jun 2023 08:15:15 +0000 Message-Id: <20230609081518.3039120-5-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 Content-Transfer-Encoding: quoted-printable X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Qi Zheng This reverts commit 20cd1892fcc3efc10a7ac327cc3790494bec46b5. 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. Therefor= e, 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@inte= l.com Signed-off-by: Qi Zheng --- mm/shrinker_debug.c | 25 +++++++++++++++++-------- 1 file changed, 17 insertions(+), 8 deletions(-) diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c index 2be15b8a6d0b..3ab53fad8876 100644 --- a/mm/shrinker_debug.c +++ b/mm/shrinker_debug.c @@ -5,12 +5,10 @@ #include #include #include -#include =20 /* defined in vmscan.c */ extern struct rw_semaphore shrinker_rwsem; extern struct list_head shrinker_list; -extern struct srcu_struct shrinker_srcu; =20 static DEFINE_IDA(shrinker_debugfs_ida); static struct dentry *shrinker_debugfs_root; @@ -51,13 +49,18 @@ static int shrinker_debugfs_count_show(struct seq_file = *m, void *v) struct mem_cgroup *memcg; unsigned long total; bool memcg_aware; - int ret =3D 0, nid, srcu_idx; + int ret, nid; =20 count_per_node =3D kcalloc(nr_node_ids, sizeof(unsigned long), GFP_KERNEL= ); if (!count_per_node) return -ENOMEM; =20 - srcu_idx =3D srcu_read_lock(&shrinker_srcu); + ret =3D down_read_killable(&shrinker_rwsem); + if (ret) { + kfree(count_per_node); + return ret; + } + rcu_read_lock(); =20 memcg_aware =3D shrinker->flags & SHRINKER_MEMCG_AWARE; =20 @@ -88,7 +91,8 @@ static int shrinker_debugfs_count_show(struct seq_file *m= , void *v) } } while ((memcg =3D mem_cgroup_iter(NULL, memcg, NULL)) !=3D NULL); =20 - srcu_read_unlock(&shrinker_srcu, srcu_idx); + rcu_read_unlock(); + up_read(&shrinker_rwsem); =20 kfree(count_per_node); return ret; @@ -111,8 +115,9 @@ static ssize_t shrinker_debugfs_scan_write(struct file = *file, .gfp_mask =3D GFP_KERNEL, }; struct mem_cgroup *memcg =3D NULL; - int nid, srcu_idx; + int nid; char kbuf[72]; + ssize_t ret; =20 read_len =3D size < (sizeof(kbuf) - 1) ? size : (sizeof(kbuf) - 1); if (copy_from_user(kbuf, buf, read_len)) @@ -141,7 +146,11 @@ static ssize_t shrinker_debugfs_scan_write(struct file= *file, return -EINVAL; } =20 - srcu_idx =3D srcu_read_lock(&shrinker_srcu); + ret =3D down_read_killable(&shrinker_rwsem); + if (ret) { + mem_cgroup_put(memcg); + return ret; + } =20 sc.nid =3D nid; sc.memcg =3D memcg; @@ -150,7 +159,7 @@ static ssize_t shrinker_debugfs_scan_write(struct file = *file, =20 shrinker->scan_objects(shrinker, &sc); =20 - srcu_read_unlock(&shrinker_srcu, srcu_idx); + up_read(&shrinker_rwsem); mem_cgroup_put(memcg); =20 return size; --=20 2.30.2