Re: [PATCH v5 update 30/32] mm: memcontrol: convert objcg to be per-memcg per-node type

[Qi Zheng]

On 2/26/26 10:27 AM, Shakeel Butt wrote:
> On Wed, Feb 25, 2026 at 05:44:56PM +0800, Qi Zheng wrote:
> > From: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> >
> > Convert objcg to be per-memcg per-node type, so that when reparent LRU
> > folios later, we can hold the lru lock at the node level, thus avoiding
> > holding too many lru locks at once.
> >
> > Signed-off-by: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
> > ---
> > changlog:
> >   - fix a missing root_obj_cgroup conversion and completely delete
> >     root_obj_cgroup.
> >
> >   include/linux/memcontrol.h | 23 +++++------
> >   include/linux/sched.h      |  2 +-
> >   mm/memcontrol.c            | 79 +++++++++++++++++++++++---------------
> >   3 files changed, 62 insertions(+), 42 deletions(-)
> >
> > diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> > index 45d911dd903e7..6e11552a90618 100644
> > --- a/include/linux/memcontrol.h
> > +++ b/include/linux/memcontrol.h
> > @@ -116,6 +116,16 @@ struct mem_cgroup_per_node {
> >   	unsigned long		lru_zone_size[MAX_NR_ZONES][NR_LRU_LISTS];
> >   	struct mem_cgroup_reclaim_iter	iter;
> >   
> > +	/*
> > +	 * objcg is wiped out as a part of the objcg repaprenting process.
> > +	 * orig_objcg preserves a pointer (and a reference) to the original
> > +	 * objcg until the end of live of memcg.
> > +	 */
> > +	struct obj_cgroup __rcu	*objcg;
> > +	struct obj_cgroup	*orig_objcg;
>
> The layout of struct mem_cgroup_per_node is very performance sensitive. Please
> couple of performance benchmarks after rearranging the fields particularly the
> above two pointers together at the start of the struct.

Got it, will try to do it. Additionally, it would be even better if
there were existing test cases available. ;)

> Otherwise:
>
> Acked-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>

Thanks!