Re: [PATCH v2 06/28] mm: memcontrol: allocate object cgroup for non-kmem case

[Johannes Weiner]

On Wed, Dec 17, 2025 at 03:27:30PM +0800, Qi Zheng wrote:
> From: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> 
> 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.

Not a big deal, but since the coverletter will be preserved in git, I
don't think you need to repeat the full thesis.

> 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.

"To allow LRU page reparenting, the objcg infrastructure [...]"

> 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@xxxxxxxxxxxxx>
> Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> Reviewed-by: Harry Yoo <harry.yoo@xxxxxxxxxx>

Looks good to me.

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>