From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out30-101.freemail.mail.aliyun.com (out30-101.freemail.mail.aliyun.com [115.124.30.101]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E39E31CD2C for ; Fri, 4 Sep 2026 02:10:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=115.124.30.101 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788487830; cv=none; b=nqpPznDUliLpIhZRDEit99cRXzu1xBpfc8ryo1whEyaFUrlOCynrdtR7/kmfOxVfVgibH4txczv54Zalm85OaK4gMk2vJ404oh4qoC2PfAXh5oZ9a1wh4lF0tWIYbh0fHe5nKlbTvXf17WIj/tz7NFgG928gPCE4/Ghw3rOzxNk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788487830; c=relaxed/simple; bh=TvrAl2cYMtM+/ORC2WefEChu8OnPh6WDj583uPi1jAQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZdTGjc9lv0Ru2WebDLVr8ixfbbeCd30KICfV1pc4SV12XED5jECU4ZpCcJagoZT9UnK3/AxK0KgjzkCMobD2Fm/jhc3AFmxzZeYKl5bJKdYmQv7oX8Muake85PdCumL6gogzAiI8HR4T+3QknqyPzN/ENpu4gcI+wMjGecjS47A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com; spf=pass smtp.mailfrom=linux.alibaba.com; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b=w/8PNvjb; arc=none smtp.client-ip=115.124.30.101 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.alibaba.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.alibaba.com header.i=@linux.alibaba.com header.b="w/8PNvjb" DKIM-Signature:v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1788487824; h=Message-ID:Date:MIME-Version:Subject:To:From:Content-Type; bh=J+SHGWUY7CbETPDlAl8WdiZ5m/7wagn5ECpymwWOZn0=; b=w/8PNvjblp7RmBFdKubmxBQBCYmaCVsTgeD3sgfxrlLpAzMSUBXdOwHrwFriourbvjt7HRvdbIqJAJVdz0ondCmGuxzWUYCxAoxA5YSz9e3FLUwEkN5+ORKv9Dgbx0aeV//IHVJ7B9kO9QWlZPIgk8c7za0xpQCvbp7rDqYoagA= X-Alimail-AntiSpam:AC=PASS;BC=-1|-1;BR=01201311R111e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=maildocker-contentspam033037026112;MF=qinyuntan@linux.alibaba.com;NM=1;PH=DS;RN=13;SR=0;TI=SMTPD_---0XAHIyJ-_1788487822; Received: from 30.178.82.219(mailfrom:qinyuntan@linux.alibaba.com fp:SMTPD_---0XAHIyJ-_1788487822 cluster:ay36) by smtp.aliyun-inc.com; Fri, 04 Sep 2026 10:10:23 +0800 Message-ID: <697713c4-0857-485b-aba7-c74f37a3c8b4@linux.alibaba.com> Date: Fri, 4 Sep 2026 10:10:20 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/list_lru: don't copy stale shrinker id from non-memcg-aware shrinkers To: =?UTF-8?Q?Michal_Koutn=C3=BD?= Cc: Johannes Weiner , Andrew Morton , Lance Yang , Qi Zheng , Roman Gushchin , Muchun Song , Dave Chinner , Baolin Wang , David Hildenbrand , Xunlei Pang , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260901115104.2944996-1-qinyuntan@linux.alibaba.com> <0c5aba0f-137a-4aaf-bddc-060118322602@linux.alibaba.com> From: Qinyun Tan In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi, Michal On 9/3/26 5:20 PM, Michal Koutný wrote: > On Thu, Sep 03, 2026 at 12:06:53PM +0800, Qinyun Tan wrote: >> You're right, that sentence is imprecise - SHRINKER_NONSLAB shrinkers >> do register per-memcg under nokmem. What I meant is that on a system >> where no NONSLAB shrinker happens to register, shrinker_nr_max stays 0. > > And ideally, with cgroup.memory=nokmem no slab-based code should call > set_shrinker_bit() with whatever shrinker_id. > Agreed, and with this patch that holds: slab-based lrus fall back to shrinker_id == -1 and set_shrinker_bit() is never reached. >> That said, I see the flag restoration and this patch as complementary >> rather than either-or: > > Yes, it fixes your immediate issue and it is a prudent approach in > list_lru_init(). OTOH, with this fixup, we won't be able to learn about > shrinkers that are missing SHRINKER_NONSLAB. > True. Though the old behavior wasn't a reliable canary either: the warning only fired while shrinker_nr_max was still 0. Once any SHRINKER_NONSLAB shrinker had expanded the maps, a missing flag showed up as a silently mis-set bit 0 rather than a warning. With your audit below covering the current tree, I think losing that accidental signal is an acceptable trade-off. > >> other MEMCG_AWARE-but-not-NONSLAB shrinkers >> (superblock, workingset shadow nodes) still take the fallback path >> under nokmem by design, and __list_lru_init() copying an unassigned >> id there is a landmine independent of the deferred split case. So I >> think this patch is still wanted as the generic fix, with the flag >> restoration on top for THP. >> >> (zswap might deserve the same NONSLAB treatment as THP, btw - its >> entries resolve the memcg from the folio's objcg, which is available >> regardless of nokmem.) > > _That_ is an important point. > So that would need a fix too, and likely Fixes: b5ba474f3f518 ("zswap: > shrink zswap pool based on memory pressure"). > Will do. > (I'd have preferred if there weren't Fixes: 03375203e1da8 which honors > the SHRINKER_NONSLAB semantics and it only uncovered pre-existing > missing flags. Or keep that Fixes: but explain the relation to the other > commits. (To make it clear to backporters.)) > Fair point. I'd propose retargeting the tag to Fixes: fafaeceb89a5e ("mm: switch deferred split shrinker to list_lru") as that is the commit that made the problem user-visible: it put a list_lru holding charged user folios behind a fallback shrinker, and the boot-time warning is reproducible from v7.2 on. Does that work for you? Andrew, thanks for the sentence fixup yesterday. If Michal agrees, could you please also retarget the Fixes: tag: -Fixes: 03375203e1da8 ("mm: do not allocate shrinker info with cgroup.memory=nokmem") +Fixes: fafaeceb89a5e ("mm: switch deferred split shrinker to list_lru") >> Would you like me to send a separate patch restoring SHRINKER_NONSLAB >> in thp_shrinker_init() (Fixes: fafaeceb89a5e)? Happy to do so if >> that works for you. > > SHRINKER_MEMCG_AWARE are due to be checked for correct marking with > SHRINKER_NONSLAB. I can see that it is missing in: thp-deferred_split, > zswap-shrinker in the v7.3-rc1. (The shrinkers in nfs42xattr.c seem to > be slab-based so they're correct.) > Thanks for auditing the whole tree. I'll send a two-patch series restoring/adding SHRINKER_NONSLAB for thp-deferred_split (Fixes: fafaeceb89a5e) and zswap-shrinker (Fixes: b5ba474f3f518). > The shrinkers mentioned in your original commit message: workingset > shadow nodes, superblock lrus are both slab-based, so systemd with only > those shouldn't be affected by this bug. > Right - they were listed only as lrus that end up carrying the bogus id 0, not as triggers; as the changelog notes, their objects resolve to a NULL memcg under nokmem so set_shrinker_bit() is never called for them. The only actual trigger is thp-deferred_split. > Thanks, > Michal Thanks, Qinyun Tan