From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-171.mta1.migadu.com (out-171.mta1.migadu.com [95.215.58.171]) (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 E3BBB23EAA0 for ; Mon, 20 Jul 2026 02:23:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.171 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784514238; cv=none; b=QlnZ+CkVOKXEZLDSwmmMPjfp0mehIPnJWhkg6Eq9nva8cjBkSR2GNm+1BNLSIABCwQm6OcEZxOnEYDWOfJ8lNLWklaUCNTgwM+0avKIQWPtrJqWYpRUR0jSPuPIU1cpqlCUDN81qMwRgnhRsL7TsgKbLo1YRhASVdW+/D8AmuCo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784514238; c=relaxed/simple; bh=z1dUIPn5zZxx4L79rGXrMiW655gMTDUnbJO9GzsftCY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=QZabjUzsfpQHtknP7QPjxzqLMl6d66wGS0hrbIq9tCV9El6v7vCYvcI8Vr5jTq/CJKyM7SzSoO+pUv5FbhzesahdVE1JLjfuhSDzT0ai+Ss7XyCaH1G08cPsgjizlc4qwjvWCFNRdx7u+1lLnkmuZaFcoB+1N8VxA4bJ0Pd+EHk= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=J91TRnw/; arc=none smtp.client-ip=95.215.58.171 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="J91TRnw/" Message-ID: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1784514233; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=p8X2N36SkSYXjR3Lmfvw9oc82NSEhF0xR/1+TvWCook=; b=J91TRnw/4A5FT66aJBIZ+uOdUSXLsRzfDF3RvMU8zEjoBvqfQAoDKQkOq0W9YGBjOm2SfO G689c4vi4VadKqANJ6lfllc2vTi49Fbw+SaVc6EYEU/Y0ij5BjMCDmMdhCzCUKoJ7BBf9a DXxPAxpQZWms4TkrGowKF3I7Kav/1dU= Date: Mon, 20 Jul 2026 10:23:41 +0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH] mm: shmem: make unused huge shrinker memcg aware To: Baolin Wang , hughd@google.com, akpm@linux-foundation.org, usama.arif@linux.dev Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20260714031918.308-1-qi.zheng@linux.dev> <7624107f-6a2d-4959-b2ee-aa362a8972eb@linux.alibaba.com> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Qi Zheng In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Hi Baolin, On 7/17/26 8:50 PM, Baolin Wang wrote: > > > On 7/15/26 5:55 PM, Qi Zheng wrote: >> Hi Baolin, > > Sorry for late reply. > >> On 7/15/26 5:37 PM, Baolin Wang wrote: >>> Hi Qi, >>> >>> On 7/14/26 11:19 AM, Qi Zheng wrote: >>>> From: Qi Zheng >>>> >>>> The shmem unused huge shrinker keeps a per-superblock list of inodes >>>> whose >>>> tail huge folio extends beyond i_size. Since that list is not memcg >>>> aware, >>>> reclaim triggered by one memcg can scan inodes from the whole >>>> superblock >>>> and split shmem huge folios charged to unrelated memcgs. >>>> >>>> Convert the shrink list to a memcg-aware list_lru. Queue each inode >>>> on the >>>> list_lru sublist matching the memcg and node of the current tail huge >>>> folio, so non-root memcg reclaim only walks candidates charged to the >>>> reclaiming memcg. Global reclaim, root memcg reclaim and shmem quota >>>> reclaim keep global semantics. >>>> >>>> The list_lru still tracks inodes while the actual split target is the >>>> current tail huge folio, so validate the folio memcg/node during >>>> scan. If >>>> the folio no longer matches the reclaim context or splitting cannot >>>> proceed, requeue the inode according to the current tail folio; if the >>>> inode is no longer shrinkable, drop the scan entry. >>>> >>>> This can be tested with the shrinker debugfs interface by allocating 32 >>>> tmpfs tail THPs in each of two memcgs, then scanning the sb-tmpfs >>>> shrinker >>>> with memcg A's cgroup id: >>>> >>>>                 before A scan        after A scan >>>>    base         A=64M, B=64M         A=0,  B=0 >>>>    patched      A=64M, B=64M         A=0,  B=64M >>>> >>>> Signed-off-by: Qi Zheng >>>> --- >>> >>> Thanks for your patch. This work has been on my TODO list for a while :) >>> >>> Overall it looks good. I'll take a closer look and run some tests. >> >> Thanks! >> >>> >>>> This patch is based on next-20260701 because it doesn't include this >>>> patch: >>>> >>>> https://lore.kernel.org/all/20260609123047.1948242-1- >>>> usama.arif@linux.dev/ >>>> >>>> Later on, Usama will consider moving this restriction down into the >>>> fs callback. >>>> >>>>   include/linux/shmem_fs.h |  14 +- >>>>   mm/shmem.c               | 379 +++++++++++++++++++++++++++++ >>>> +--------- >>>>   2 files changed, 310 insertions(+), 83 deletions(-) >>>> >>>> diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h >>>> index e729b9b0e38d4..0b14de1e890a9 100644 >>>> --- a/include/linux/shmem_fs.h >>>> +++ b/include/linux/shmem_fs.h >>>> @@ -11,6 +11,7 @@ >>>>   #include >>>>   #include >>>>   #include >>>> +#include >>>>   struct swap_iocb; >>>> @@ -56,6 +57,13 @@ struct shmem_inode_info { >>>>       struct dquot __rcu    *i_dquot[MAXQUOTAS]; >>>>   #endif >>>>       struct inode        vfs_inode; >>>> + >>>> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE >>>> +    struct list_head    shrinklist_scan; >>> >>> Why introduce another list_head member? Why can't we reuse >>> 'shrinklist' in this structure? In other words, if we isolate this >>> inode from list_lru, then 'inode_info->shrinklist' can be reused to >>> link it into the temporary list, right? >> >> After list_lru isolation, the shrinker drops the list_lru lock and >> processes the inode on a local scan list. During that time, shmem >> faults can make the inode's current tail huge folio change, and >> shmem_unused_huge_add() may need to queue the same inode again on >> the active list_lru, possibly under a different memcg/node sublist. >> >> If we reused info->shrinklist for the temporary scan list, then while >> the inode is being scanned: >> >> 1. info->shrinklist would be non-empty because it is on the local scan >>     list, so shmem_unused_huge_add() could not tell that the inode is no >>     longer on the active list_lru. >> 2. Re-adding it to list_lru with the same list_head would corrupt the >>     local scan list. > > Right. Just some preliminary thoughts: > > If the current inode needs to be re-added to the list_lru, it means the > inode's i_size has changed. If 'info->shrinklist' is on the temporary > list at this point, we can follow the same logic as the original 'info- > >shrinklist' handling and simply skip the re-adding to list_lru. > Instead, we can let shmem_unused_huge_shrink() get the end folio via > filemap_get_entry(i_size), and then check the memcg and nid — if they > differ from the 'sc', we can re-add the inode back to the list_lru in > shmem_unused_huge_shrink(). That also sounds workable. > > Of course, there may be other races that need to be considered as well. I will look into it. > > In any case, we should try to avoid adding too many members to the > 'shmem_inode_info' struct, since when there are many tmpfs files this > could introduce noticeable memory overhead. Got it. Thanks, Qi > >> 3. Skipping the add would lose the new current tail huge folio if the >>     scan later drops the old scan entry instead of requeueing it. >> >> So isolation removes the inode from the active list_lru and leaves >> info->shrinklist empty. A concurrent fault can safely add the inode back >> to the active list_lru with the current folio's memcg/node, while the >> shrinker still owns the old scan entry through shrinklist_scan. The scan >> loop then detects that re-add and drops the stale scan entry, leaving >> the active entry for a later scan. >> >>> >>>> +    struct mem_cgroup    *shrinklist_memcg; >>>> +    int            shrinklist_nid; >>>> +    bool            shrinklist_isolated; >>> >>> Do we need an extra bool to indicate whether it's isolated? Can't we >>> just use 'list_empty(inode_info->shrinklist)'? I may have missed some >>> details. >> >> list_empty(info->shrinklist) cannot be used for this. That list node >> tracks active list_lru membership only. But you are right that the >> explicit bool is not necessary, we can use list_empty(&info- >>  >shrinklist_scan) instead. >> >> Thanks, >> Qi >> >> >