From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: [PATCH v4 0/4] mm/page_owner: Extend page_owner to show memcg information Date: Wed, 2 Feb 2022 15:30:32 -0500 Message-ID: <20220202203036.744010-1-longman@redhat.com> References: <20220131192308.608837-5-longman@redhat.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1643833967; 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=wcENReRHFRW4er+uIjMQ9SA6VL83pYAObKBta+stQfk=; b=Oua1l7DJd7u+b4XmbJ1xBBfUnFT2dq+3PlvBE92yxSCsnZWCLMg1WW5FRmixEHICW8x6lf DXka72rZgFB6Dd6MCqZeYrnr/EgoK/ykHUurh4GJ/YV/f1jibL7FfUatburHjLrAfuqJ4j zd19mnv9f/32c3v9taaLkoHFP4+E+/w= In-Reply-To: <20220131192308.608837-5-longman@redhat.com> List-ID: Content-Type: text/plain; charset="us-ascii" To: Johannes Weiner , Michal Hocko , Vladimir Davydov , Andrew Morton , Petr Mladek , Steven Rostedt , Sergey Senozhatsky , Andy Shevchenko , Rasmus Villemoes Cc: linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, Ira Weiny , Mike Rapoport , David Rientjes , Roman Gushchin , Rafael Aquini , Waiman Long v4: - Take rcu_read_lock() when memcg is being accessed as suggested by Michal. - Make print_page_owner_memcg() return the new offset into the buffer and put CONFIG_MEMCG block inside as suggested by Mike. - Directly use TASK_COMM_LEN as length of name buffer as suggested by Roman. v3: - Add unlikely() to patch 1 and clarify that -1 will not be returned. - Use a helper function to print out memcg information in patch 3. - Add a new patch 4 to store task command name in page_owner structure. v2: - Remove the SNPRINTF() macro as suggested by Ira and use scnprintf() instead to remove some buffer overrun checks. - Add a patch to optimize vscnprintf with a size parameter of 0. While debugging the constant increase in percpu memory consumption on a system that spawned large number of containers, it was found that a lot of offline mem_cgroup structures remained in place without being freed. Further investigation indicated that those mem_cgroup structures were pinned by some pages. In order to find out what those pages are, the existing page_owner debugging tool is extended to show memory cgroup information and whether those memcgs are offline or not. With the enhanced page_owner tool, the following is a typical page that pinned the mem_cgroup structure in my test case: Page allocated via order 0, mask 0x1100cca(GFP_HIGHUSER_MOVABLE), pid 162970 (podman), ts 1097761405537 ns, free_ts 1097760838089 ns PFN 1925700 type Movable Block 3761 type Movable Flags 0x17ffffc00c001c(uptodate|dirty|lru|reclaim|swapbacked|node=0|zone=2|lastcpupid=0x1fffff) prep_new_page+0xac/0xe0 get_page_from_freelist+0x1327/0x14d0 __alloc_pages+0x191/0x340 alloc_pages_vma+0x84/0x250 shmem_alloc_page+0x3f/0x90 shmem_alloc_and_acct_page+0x76/0x1c0 shmem_getpage_gfp+0x281/0x940 shmem_write_begin+0x36/0xe0 generic_perform_write+0xed/0x1d0 __generic_file_write_iter+0xdc/0x1b0 generic_file_write_iter+0x5d/0xb0 new_sync_write+0x11f/0x1b0 vfs_write+0x1ba/0x2a0 ksys_write+0x59/0xd0 do_syscall_64+0x37/0x80 entry_SYSCALL_64_after_hwframe+0x44/0xae Charged to offline memcg libpod-conmon-15e4f9c758422306b73b2dd99f9d50a5ea53cbb16b4a13a2c2308a4253cc0ec8. So the page was not freed because it was part of a shmem segment. That is useful information that can help users to diagnose similar problems. With cgroup v1, /proc/cgroups can be read to find out the total number of memory cgroups (online + offline). With cgroup v2, the cgroup.stat of the root cgroup can be read to find the number of dying cgroups (most likely pinned by dying memcgs). The page_owner feature is not supposed to be enabled for production system due to its memory overhead. However, if it is suspected that dying memcgs are increasing over time, a test environment with page_owner enabled can then be set up with appropriate workload for further analysis on what may be causing the increasing number of dying memcgs. Waiman Long (4): lib/vsprintf: Avoid redundant work with 0 size mm/page_owner: Use scnprintf() to avoid excessive buffer overrun check mm/page_owner: Print memcg information mm/page_owner: Record task command name lib/vsprintf.c | 8 +++--- mm/page_owner.c | 70 ++++++++++++++++++++++++++++++++++++++----------- 2 files changed, 60 insertions(+), 18 deletions(-) -- 2.27.0