linux-kernel - Re: [PATCH -next 1/5] mm/mglru: use mem_cgroup

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Message-ID: <8aff3f15-79d6-48a0-a63d-735fabf6759d@huaweicloud.com>
Date: Tue, 23 Dec 2025 08:45:38 +0800
From: Chen Ridong <chenridong@...weicloud.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: akpm@...ux-foundation.org, axelrasmussen@...gle.com, yuanchu@...gle.com,
 weixugc@...gle.com, david@...nel.org, lorenzo.stoakes@...cle.com,
 Liam.Howlett@...cle.com, vbabka@...e.cz, rppt@...nel.org, surenb@...gle.com,
 mhocko@...e.com, corbet@....net, hannes@...xchg.org,
 roman.gushchin@...ux.dev, muchun.song@...ux.dev, zhengqi.arch@...edance.com,
 linux-mm@...ck.org, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
 cgroups@...r.kernel.org, lujialin4@...wei.com, zhongjinji@...or.com
Subject: Re: [PATCH -next 1/5] mm/mglru: use mem_cgroup_iter for global
 reclaim



On 2025/12/23 5:18, Shakeel Butt wrote:
> On Mon, Dec 22, 2025 at 03:27:26PM +0800, Chen Ridong wrote:
>>
> [...]
>>
>>>> -		if (should_abort_scan(lruvec, sc))
>>>> +		if (should_abort_scan(lruvec, sc)) {
>>>> +			if (cookie)
>>>> +				mem_cgroup_iter_break(target, memcg);
>>>>  			break;
>>>
>>> This seems buggy as we may break the loop without calling
>>> mem_cgroup_iter_break(). I think for kswapd the cookie will be NULL and
>>> if should_abort_scan() returns true, we will break the loop without
>>> calling mem_cgroup_iter_break() and will leak a reference to memcg.
>>>
>>
>> Thank you for catching that—my mistake.
>>
>> This also brings up another point: In kswapd, the traditional LRU iterates through all memcgs, but
>> stops for the generational LRU (GENLRU) when should_abort_scan is met (i.e., enough pages are
>> reclaimed or the watermark is satisfied). Shouldn't both behave consistently?
>>
>> Perhaps we should add should_abort_scan(lruvec, sc) in shrink_node_memcgs for the traditional LRU as
>> well?
> 
> We definitely should discuss about should_abort_scan() for traditional
> reclaim but to keep things simple, let's do that after this series. For
> now, follow Johannes' suggestion of lru_gen_should_abort_scan().
> 

Okey, understood.

-- 
Best regards,
Ridong