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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1652121524; 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=G0nsxyzGb1i11ycGLFmpikTl6TwBBRGWt6VA6PTf/VI=; b=MGMq29EFa8FQSOBa6oumVjlBpR2OcRgE4ObbYzl2jTIkeEugSFzKva5kAUVdBmBYGHXCKH 5L0j+wlTWkeAq93clx7+ie2Mkn/7ttrWEW2I4TScScRoM/uIVtxtPaOmdKG/4PH2p6xyL8 eoQgEswaQWIZITazBVUeekuPoHBqq/8= From: Roman Gushchin To: Andrew Morton , linux-mm@kvack.org Cc: Dave Chinner , linux-kernel@vger.kernel.org, Kent Overstreet , Hillf Danton , Christophe JAILLET , Roman Gushchin Subject: [PATCH v3 6/6] mm: shrinkers: add scan interface for shrinker debugfs Date: Mon, 9 May 2022 11:38:20 -0700 Message-Id: <20220509183820.573666-7-roman.gushchin@linux.dev> In-Reply-To: <20220509183820.573666-1-roman.gushchin@linux.dev> References: <20220509183820.573666-1-roman.gushchin@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Migadu-Auth-User: linux.dev X-Spam-Status: No, score=-2.0 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RDNS_NONE,SPF_HELO_NONE,T_SCC_BODY_TEXT_LINE autolearn=no 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 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; + 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; + + if (shrinker->flags & SHRINKER_MEMCG_AWARE) { + memcg = mem_cgroup_get_from_ino(ino); + if (!memcg || IS_ERR(memcg)) + return -ENOENT; + + if (!mem_cgroup_online(memcg)) { + mem_cgroup_put(memcg); + return -ENOENT; + } + } else { + if (ino != 0) + return -EINVAL; + memcg = NULL; + } + + 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; +} + +static const struct file_operations shrinker_debugfs_scan_fops = { + .owner = THIS_MODULE, + .open = shrinker_debugfs_scan_open, + .write = shrinker_debugfs_scan_write, +}; + int shrinker_debugfs_add(struct shrinker *shrinker) { struct dentry *entry; @@ -130,6 +201,8 @@ int shrinker_debugfs_add(struct shrinker *shrinker) debugfs_create_file("count", 0220, entry, shrinker, &shrinker_debugfs_count_fops); + debugfs_create_file("scan", 0440, entry, shrinker, + &shrinker_debugfs_scan_fops); return 0; } -- 2.35.3