linux-kernel - Re: [PATCH v1 05/26] mm: memcontrol: allocate object cgroup for non-kmem case

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Message-ID: <aRrWgxZ0kxtcBcJ6@hyeyoo>
Date: Mon, 17 Nov 2025 17:02:11 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: Qi Zheng <qi.zheng@...ux.dev>
Cc: hannes@...xchg.org, hughd@...gle.com, mhocko@...e.com,
        roman.gushchin@...ux.dev, shakeel.butt@...ux.dev,
        muchun.song@...ux.dev, david@...hat.com, lorenzo.stoakes@...cle.com,
        ziy@...dia.com, imran.f.khan@...cle.com, kamalesh.babulal@...cle.com,
        axelrasmussen@...gle.com, yuanchu@...gle.com, weixugc@...gle.com,
        akpm@...ux-foundation.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        Muchun Song <songmuchun@...edance.com>,
        Qi Zheng <zhengqi.arch@...edance.com>
Subject: Re: [PATCH v1 05/26] mm: memcontrol: allocate object cgroup for
 non-kmem case

On Tue, Oct 28, 2025 at 09:58:18PM +0800, Qi Zheng wrote:
> From: Muchun Song <songmuchun@...edance.com>
> 
> Pagecache pages are charged at allocation time and hold a reference
> to the original memory cgroup until reclaimed. Depending on memory
> pressure, page sharing patterns between different cgroups and cgroup
> creation/destruction rates, many dying memory cgroups can be pinned
> by pagecache pages, reducing page reclaim efficiency and wasting
> memory. Converting LRU folios and most other raw memory cgroup pins
> to the object cgroup direction can fix this long-living problem.
> 
> As a result, the objcg infrastructure is no longer solely applicable
> to the kmem case. In this patch, we extend the scope of the objcg
> infrastructure beyond the kmem case, enabling LRU folios to reuse
> it for folio charging purposes.
> 
> It should be noted that LRU folios are not accounted for at the root
> level, yet the folio->memcg_data points to the root_mem_cgroup. Hence,
> the folio->memcg_data of LRU folios always points to a valid pointer.
> However, the root_mem_cgroup does not possess an object cgroup.
> Therefore, we also allocate an object cgroup for the root_mem_cgroup.
> 
> Signed-off-by: Muchun Song <songmuchun@...edance.com>
> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
> ---

Looks good to me,
Reviewed-by: Harry Yoo <harry.yoo@...cle.com>

-- 
Cheers,
Harry / Hyeonggon