Re: [PATCH] memcg: vmalloc: simplify MEMCG_VMALLOC updates

[Shakeel Butt]

On Thu, Apr 03, 2025 at 12:47:41PM -0400, Johannes Weiner wrote:
> On Wed, Apr 02, 2025 at 10:33:26PM -0700, Shakeel Butt wrote:
> > The vmalloc region can either be charged to a single memcg or none. At
> > the moment kernel traverses all the pages backing the vmalloc region to
> > update the MEMCG_VMALLOC stat. However there is no need to look at all
> > the pages as all those pages will be charged to a single memcg or none.
> > Simplify the MEMCG_VMALLOC update by just looking at the first page of
> > the vmalloc region.
> > 
> > Signed-off-by: Shakeel Butt <shakeel.butt@xxxxxxxxx>
> 
> It's definitely pointless to handle each page with the stat being
> per-cgroup only. But I do wonder why it's not a regular vmstat item.
> 
> There is no real reason it *should* be a private memcg stat, is there?

Yes, it can be a regular vmstat item (enum node_stat_item). However then
we have go over each page as node_stat_item are per-node and vmalloc
region can have pages from different nodes (I think but let me check).