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From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: rcuiant1k3ntdkyepz65f4zagaqt489g X-Rspam-User: X-Rspamd-Queue-Id: 89C42180009 X-Rspamd-Server: rspam02 X-HE-Tag: 1782179902-959925 X-HE-Meta: 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 Y+6IRaAV 0jIMdW88IOXYnG5YJf4TgQNyejlgYOGhjVVVjtTsjydagh+nvHL0Iw4S7frS53hf704EC2//fajWzaaKojR9fiAHefyPzTTgw4xjLmsmU+n+mhcccd4O2MzKw8pz3h4a3ZaQ5KMthqu1lUdZkgt3jApIeCHzeSWvmmzaGp3/ae35V+pWZPap5VHqvSgarKVRzOTjuZukM3ajkP++KoOpBx6ws4Gvv6CIj3MO7zY4l6jP+aHpugRC6wZziuIREdvOOFkY84VvK/BmRuyhrpV7YjLD8wiwr5aGoLsIG Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Barry, On 6/23/26 6:52 AM, Barry Song wrote: > On Mon, Jun 22, 2026 at 3:38 PM Qi Zheng wrote: >> >> From: Qi Zheng >> >> The mglru page table walker batches per-generation size deltas in >> walk->nr_pages while walking page tables without holding the lruvec lock. >> The reset_batch_size() later folds those deltas into walk->lruvec under >> the lruvec lock. >> >> The page table walker can run concurrently with the memcg reparenting path >> as follows: >> >> CPU0 CPU1 >> ==== ==== >> >> walk_mm >> --> walk_page_range >> --> update_batch_size >> --> walk->nr_pages += delta >> >> mem_cgroup_css_offline >> --> memcg_reparent_objcgs >> --> lock lruvec >> lru_gen_reparent_memcg >> --> reparent child folios to parent >> unlock lruvec >> >> lock lruvec >> reset_batch_size >> --> child lrugen->nr_pages += delta >> >> This can trigger the following warning: >> >> WARNING: mm/vmscan.c:5867 at lru_gen_exit_memcg+0x26f/0x300 >> RIP: 0010:lru_gen_exit_memcg+0x26f/0x300 mm/vmscan.c:5867 > > I can't find 5867; instead, I can find 5828: > > VM_WARN_ON_ONCE(memchr_inv(lruvec->lrugen.nr_pages, 0, > sizeof(lruvec->lrugen.nr_pages))); > > Is this the warning? Yes, I just copy-pasted the warning log from Peiyang's report. Maybe the description should be changed to: This will trigger the following warning in lru_gen_exit_memcg(): VM_WARN_ON_ONCE(memchr_inv(lruvec->lrugen.nr_pages, 0, sizeof(lruvec->lrugen.nr_pages))); > >> Call Trace: >> >> mem_cgroup_free mm/memcontrol.c:3972 [inline] >> mem_cgroup_css_free+0x76/0xb0 mm/memcontrol.c:4241 >> css_free_rwork_fn+0x125/0x1260 kernel/cgroup/cgroup.c:5575 >> process_one_work+0xa0d/0x1c30 kernel/workqueue.c:3314 >> process_scheduled_works kernel/workqueue.c:3397 [inline] >> worker_thread+0x645/0xe80 kernel/workqueue.c:3478 >> kthread+0x367/0x480 kernel/kthread.c:436 >> ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158 >> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 >> >> >> To fix it, add lrugen->reparented to remember the new owner of a >> reparented lruvec, and make reset_batch_size() charge pending deltas to >> that owner. >> >> Reported-by: Peiyang He >> Closes: https://lore.kernel.org/all/5A9E929D82717101+12fcf643-efb8-4b9a-a53a-1e28cc894f0b@smail.nju.edu.cn >> Fixes: f304652609ea ("mm: vmscan: prepare for reparenting MGLRU folios") >> Cc: >> Signed-off-by: Qi Zheng > > Looks reasonable to me. > Reviewed-by: Barry Song Thanks!