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

[Qi Zheng]

On 12/18/25 5:22 AM, Johannes Weiner wrote:
> 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.

Got it.

> > 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 [...]"

OK, will do.

> > 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>

Thanks!