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Received: from 30.178.85.189(mailfrom:qinyuntan@linux.alibaba.com fp:SMTPD_---0XCNdeuW_1791452367 cluster:ay36) by smtp.aliyun-inc.com; Thu, 08 Oct 2026 17:39:33 +0800 Message-ID: <01f89ece-9d46-47f2-b660-d32ab5d32923@linux.alibaba.com> Date: Thu, 8 Oct 2026 17:39:26 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/4] mm: memcontrol: drop kmemcg_id and use mem_cgroup_id() for list_lru indexing To: Kairui Song Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , =?UTF-8?Q?Michal_Koutn=C3=BD?= , David Hildenbrand , Zi Yan , Baolin Wang , Usama Arif , Dave Chinner , Qi Zheng , Yosry Ahmed , Nhat Pham , Chengming Zhou , Xunlei Pang , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260910080722.3961351-1-qinyuntan@linux.alibaba.com> <20260910080722.3961351-2-qinyuntan@linux.alibaba.com> From: Qinyun Tan In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 771F0C0004 X-Rspam-User: X-Stat-Signature: smbqb4c8ag4aip9418skopn6sxbxm1kb X-HE-Tag: 1791452378-564190 X-HE-Meta: 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 Nkm5MX9r /12F2q7aTrkUdqQYdFis46inxn6E4ARp0Nt8cp/mg5zilfVY52HWfSDg2B6yxY+cSYbz1OzazMQWJo+jgFIgnRXAuLXPPl8JSBJJlN60n3VgkQlpdPsuCXX5Nyy36kxpQC+W9FtMjfSCoiK/T/JrIpINO0EkyaBnONklwBiDslgvEdH9+S+9/oaMhgqjQHeTKXh9C/Gh1PLcwEbURyTwDcJX4erfzzmN6oF8FnOl7dX+bMUZbFS2CLcT15hiaAhE8A5N7joVVT40yRSET/Lvc//q5FW9hh3m3eskN9WE/NY+Ohqajn8TgLpDOT+2gRcsOP5GUDAVCTkj8xNl39SAHPOlHN5s2o0lKSnTWXBZOd9FLnxo= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 9/27/26 4:29 AM, Kairui Song wrote: > > Hi Qinyun > > With this commit, my arm64 VM hangs at every boot with a > 100%-reproducible infinite loop in xas_find(), driven by > the dcache shrinker during the first remount of the root filesystem. > Reverting this fixes the issue: > > CPU: 2 UID: 0 PID: 579 Comm: mount Not tainted > 7.3.0-rc4.orig-00725-g09d9672a5d4f #33 PREEMPT(full) > pc : xas_find+0x184/0x1c8 > lr : xas_find+0x6c/0x1c8 > Call trace: > xas_find+0x184/0x1c8 > xa_find_after+0x88/0x120 > list_lru_walk_node+0xc0/0x2a0 > shrink_dcache_sb+0x80/0x130 > reconfigure_super+0xc0/0x1f8 > vfs_fsconfig_locked+0xa8/0x120 > __arm64_sys_fsconfig+0x280/0x33c > > Just for reference, this also fixed it: > > diff --git a/mm/list_lru.c b/mm/list_lru.c > index 7dbb6125cb1d..42c48c3b9235 100644 > --- a/mm/list_lru.c > +++ b/mm/list_lru.c > @@ -427,13 +427,13 @@ unsigned long list_lru_walk_node(struct list_lru > *lru, int nid, > unsigned long index; > > xa_for_each(&lru->xa, index, mlru) { > - rcu_read_lock(); > - memcg = mem_cgroup_from_private_id(index); > - if (!memcg || !mem_cgroup_tryget(memcg)) { > - rcu_read_unlock(); > + memcg = mem_cgroup_get_from_id(index); > + if (!memcg) > continue; > - } > - rcu_read_unlock(); > isolated += __list_lru_walk_one(lru, nid, memcg, > isolate, cb_arg, > nr_to_walk, false); > > === > > And BTW cgroup ID lookups seem much heavier, not sure about the > performance impact. Hi Kairui, Thanks for tracking this down. I missed the reverse lookup in list_lru_walk_node() when switching to cgroup IDs. Your change fixes that mismatch. There is a catch with mem_cgroup_get_from_id(), though: it calls cgroup_get_from_id(), which only looks up cgroups visible in the current task's cgroup namespace. Here we need to walk all memcgs on the LRU, including those outside that namespace, so we need a lookup without that restriction. Thanks, Qinyun Tan