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

[Shakeel Butt]

On Thu, Apr 03, 2025 at 01:17:22PM +0200, Uladzislau Rezki 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>
> > ---
> >  mm/vmalloc.c | 13 +++++--------
> >  1 file changed, 5 insertions(+), 8 deletions(-)
> > 
> > diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> > index 3ed720a787ec..cdae76994488 100644
> > --- a/mm/vmalloc.c
> > +++ b/mm/vmalloc.c
> > @@ -3370,12 +3370,12 @@ void vfree(const void *addr)
> >  
> >  	if (unlikely(vm->flags & VM_FLUSH_RESET_PERMS))
> >  		vm_reset_perms(vm);
> > +	if (vm->nr_pages && !(vm->flags & VM_MAP_PUT_PAGES))
> > +		mod_memcg_page_state(vm->pages[0], MEMCG_VMALLOC, -vm->nr_pages);
> >
> Could you please add a comment stating that the first page should be
> modified?
> 

Sorry, what do you mean by first page should be modified?
mod_memcg_page_state() will not modify the page but extract memcg from
it and modify its vmalloc stat.


> Yes, the comment is clear, but git blame/log takes time.
> 
> Reviewed-by: Uladzislau Rezki (Sony) <urezki@xxxxxxxxx>

Thanks.

> 
> --
> Uladzislau Rezki