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[2620:137:e000::1:20]) by mx.google.com with ESMTP id l9-20020a170906794900b006e894a5efc6si19865179ejo.542.2022.05.23.19.52.36; Mon, 23 May 2022 19:53:01 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@bytedance-com.20210112.gappssmtp.com header.s=20210112 header.b=WyOkLilJ; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=bytedance.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232741AbiEXCX6 (ORCPT + 99 others); Mon, 23 May 2022 22:23:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49086 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229888AbiEXCX4 (ORCPT ); Mon, 23 May 2022 22:23:56 -0400 Received: from mail-pg1-x529.google.com (mail-pg1-x529.google.com [IPv6:2607:f8b0:4864:20::529]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C7A7D880FE for ; Mon, 23 May 2022 19:23:55 -0700 (PDT) Received: by mail-pg1-x529.google.com with SMTP id h186so15176610pgc.3 for ; Mon, 23 May 2022 19:23:55 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bytedance-com.20210112.gappssmtp.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=imqsWHcVz1x3U/e/rDDis/IuDhHm/2O5Z9DNKRPykt4=; b=WyOkLilJunDPIRLV5CIPabmtUHndgCWzDzEUkYf/sX0mQMP2sA8hnmBRgH0S0FP1lW 0XJHqEHz2N4A6fSbzdea1rYKd3/h4soHXWGQrSgAOJknDMRly7t5vccn1Oy4gKb7BjED 06cEJtl6Yw8bzS2QhE1iHzt7hQrYM5+h3JABKH1szxPjCmAdMRaNiggNt/a9/BvGplZh DtnZ2/mMoTpI3P08ZnUsBNm94nQaHXDRS5WC6LqUtjljHF1OpHJM6lD9s/2C+ADqZG+o asoX2IhGQhY5P6HffdkamMxmuRY/BgTIjUbDhiFlDdxrVbVjKyIzrh2e5VslEMuOKDa4 EIEA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=imqsWHcVz1x3U/e/rDDis/IuDhHm/2O5Z9DNKRPykt4=; b=GYXDUmXxsyScvWowgfRLi3DBsoVZdFByqrKWrMQ0jeQhMqTMbnGGg2My3cPd0cFhBq kFp0uwVucxyu0U9I6fYq6oTPyN1u2Sv7XgDqRyTflazCwBS1jAzyXxdV8ROZiUTezchS ddU3EWa+hygaQA9ALq2swxfo2uW430oNOVia7XsSejdLs2Zw1I5o1U4Z7D9UXWNnPM5j 8dcp/yMLfPwhBT585rlHrKDh2HWe5nSN/8JX8VAoMZhB7Ty7k66kzdbycKY68KGJg1Ym Y4Anaimdt7HoyalCx4w2pj/Z4xmSd5X2JkCH66tMPVQG7VD2D5/J2Z3km5kh2wQw3rqU mK6w== X-Gm-Message-State: AOAM531lgtXWlfXGHSdCN291WwpWJeYKrCe2bwiUBksxU0OpEC/Owm2+ x92gB9bRzfKBQc7SBJmsvKgN6g== X-Received: by 2002:a63:c10:0:b0:3da:fb56:648d with SMTP id b16-20020a630c10000000b003dafb56648dmr22365773pgl.590.1653359035312; Mon, 23 May 2022 19:23:55 -0700 (PDT) Received: from localhost ([2408:8207:18da:2310:f940:af17:c2f5:8656]) by smtp.gmail.com with ESMTPSA id be11-20020a056a001f0b00b00518764d09cdsm6767281pfb.164.2022.05.23.19.23.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 23 May 2022 19:23:55 -0700 (PDT) Date: Tue, 24 May 2022 10:23:50 +0800 From: Muchun Song To: Roman Gushchin Cc: Andrew Morton , linux-mm@kvack.org, Dave Chinner , linux-kernel@vger.kernel.org, Kent Overstreet , Hillf Danton , Christophe JAILLET Subject: Re: [PATCH v3 6/6] mm: shrinkers: add scan interface for shrinker debugfs Message-ID: References: <20220509183820.573666-1-roman.gushchin@linux.dev> <20220509183820.573666-7-roman.gushchin@linux.dev> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS, T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 23, 2022 at 01:54:24PM -0700, Roman Gushchin wrote: > On Sun, May 22, 2022 at 07:35:59PM +0800, Muchun Song wrote: > > On Mon, May 09, 2022 at 11:38:20AM -0700, Roman Gushchin wrote: > > > Add a scan interface which allows to trigger scanning of a particular > > > shrinker and specify memcg and numa node. It's useful for testing, > > > debugging and profiling of a specific scan_objects() callback. > > > Unlike alternatives (creating a real memory pressure and dropping > > > caches via /proc/sys/vm/drop_caches) this interface allows to interact > > > with only one shrinker at once. Also, if a shrinker is misreporting > > > the number of objects (as some do), it doesn't affect scanning. > > > > > > Signed-off-by: Roman Gushchin > > > --- > > > .../admin-guide/mm/shrinker_debugfs.rst | 39 +++++++++- > > > mm/shrinker_debug.c | 73 +++++++++++++++++++ > > > 2 files changed, 108 insertions(+), 4 deletions(-) > > > > > > diff --git a/Documentation/admin-guide/mm/shrinker_debugfs.rst b/Documentation/admin-guide/mm/shrinker_debugfs.rst > > > index 6783f8190e63..8fecf81d60ee 100644 > > > --- a/Documentation/admin-guide/mm/shrinker_debugfs.rst > > > +++ b/Documentation/admin-guide/mm/shrinker_debugfs.rst > > > @@ -5,14 +5,16 @@ Shrinker Debugfs Interface > > > ========================== > > > > > > Shrinker debugfs interface provides a visibility into the kernel memory > > > -shrinkers subsystem and allows to get information about individual shrinkers. > > > +shrinkers subsystem and allows to get information about individual shrinkers > > > +and interact with them. > > > > > > For each shrinker registered in the system a directory in **/shrinker/** > > > is created. The directory's name is composed from the shrinker's name and an > > > unique id: e.g. *kfree_rcu-0* or *sb-xfs:vda1-36*. > > > > > > -Each shrinker directory contains the **count** file, which allows to trigger > > > -the *count_objects()* callback for each memcg and numa node (if applicable). > > > +Each shrinker directory contains **count** and **scan** files, which allow to > > > +trigger *count_objects()* and *scan_objects()* callbacks for each memcg and > > > +numa node (if applicable). > > > > > > Usage: > > > ------ > > > @@ -43,7 +45,7 @@ Usage: > > > > > > $ cd sb-btrfs\:vda2-24/ > > > $ ls > > > - count > > > + count scan > > > > > > 3. *Count objects* > > > > > > @@ -98,3 +100,32 @@ Usage: > > > 2877 84 0 > > > 293 1 0 > > > 735 8 0 > > > + > > > +4. *Scan objects* > > > + > > > + The expected input format:: > > > + > > > + > > > + > > > + For a non-memcg-aware shrinker or on a system with no memory > > > + cgrups **0** should be passed as cgroup id. > > > + :: > > > + > > > + $ cd /sys/kernel/debug/shrinker/ > > > + $ cd sb-btrfs\:vda2-24/ > > > + > > > + $ cat count | head -n 5 > > > + 1 212 0 > > > + 21 97 0 > > > + 55 802 5 > > > + 2367 2 0 > > > + 225 13 0 > > > + > > > + $ echo "55 0 200" > scan > > > + > > > + $ cat count | head -n 5 > > > + 1 212 0 > > > + 21 96 0 > > > + 55 752 5 > > > + 2367 2 0 > > > + 225 13 0 > > > diff --git a/mm/shrinker_debug.c b/mm/shrinker_debug.c > > > index 28b1c1ab60ef..8f67fef5a643 100644 > > > --- a/mm/shrinker_debug.c > > > +++ b/mm/shrinker_debug.c > > > @@ -101,6 +101,77 @@ static int shrinker_debugfs_count_show(struct seq_file *m, void *v) > > > } > > > DEFINE_SHOW_ATTRIBUTE(shrinker_debugfs_count); > > > > > > +static int shrinker_debugfs_scan_open(struct inode *inode, struct file *file) > > > +{ > > > + file->private_data = inode->i_private; > > > + return nonseekable_open(inode, file); > > > +} > > > + > > > +static ssize_t shrinker_debugfs_scan_write(struct file *file, > > > + const char __user *buf, > > > + size_t size, loff_t *pos) > > > +{ > > > + struct shrinker *shrinker = (struct shrinker *)file->private_data; > > > > Seems we could drop the cast since ->private_data is void * type. > > Yep, fixed. Thanks! > > > > > > + unsigned long nr_to_scan = 0, ino; > > > + struct shrink_control sc = { > > > + .gfp_mask = GFP_KERNEL, > > > + }; > > > + struct mem_cgroup *memcg = NULL; > > > + int nid; > > > + char kbuf[72]; > > > + int read_len = size < (sizeof(kbuf) - 1) ? size : (sizeof(kbuf) - 1); > > > + ssize_t ret; > > > + > > > + if (copy_from_user(kbuf, buf, read_len)) > > > + return -EFAULT; > > > + kbuf[read_len] = '\0'; > > > + > > > + if (sscanf(kbuf, "%lu %d %lu", &ino, &nid, &nr_to_scan) < 2) > > > + return -EINVAL; > > > + > > > + if (nid < 0 || nid >= nr_node_ids) > > > + return -EINVAL; > > > + > > > > Should we break here if nr_to_scan is zero? > > Not a very likely scenario, but ok. > Agree. > > > > > + if (shrinker->flags & SHRINKER_MEMCG_AWARE) { > > > + memcg = mem_cgroup_get_from_ino(ino); > > > + if (!memcg || IS_ERR(memcg)) > > > > Should we drop the check of "!memcg" since mem_cgroup_get_from_ino > > cannot return NULL? > > It can if !CONFIG_MEMCG. You might argue that then shrinker can not have > the SHRINKER_MEMCG_AWARE flag, but since it's not a hot path at all, > I'll keep it for extra safety. > Make sense. > > > > > + return -ENOENT; > > > + > > > + if (!mem_cgroup_online(memcg)) { > > > + mem_cgroup_put(memcg); > > > + return -ENOENT; > > > + } > > > + } else { > > > + if (ino != 0) > > > + return -EINVAL; > > > + memcg = NULL; > > > > IIUC, memcg is already NULL if we reach here, right? Then the > > assignment is not necessary. Or we cound remove the initialization > > of 'memcg' where it is definned. > > Right, removed. > > > > > > + } > > > + > > > + ret = down_read_killable(&shrinker_rwsem); > > > + if (ret) { > > > + mem_cgroup_put(memcg); > > > + return ret; > > > + } > > > + > > > + sc.nid = nid; > > > + sc.memcg = memcg; > > > + sc.nr_to_scan = nr_to_scan; > > > + sc.nr_scanned = nr_to_scan; > > > + > > > + shrinker->scan_objects(shrinker, &sc); > > > + > > > + up_read(&shrinker_rwsem); > > > + mem_cgroup_put(memcg); > > > + > > > + return ret ? ret : size; > > > > Seems "ret" is always equal to 0 here, should we simplify this > > to "return size"? > > Right. > > Thank you for the review! > My pleasure. Thanks.