linux-kernel - Re: [PATCH] memcg: vmalloc: simplify MEMCG

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Message-ID: <Z-5uQlaPjZtB61C4@pc636>
Date: Thu, 3 Apr 2025 13:17:22 +0200
From: Uladzislau Rezki <urezki@...il.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...nel.org>,
	Roman Gushchin <roman.gushchin@...ux.dev>,
	Muchun Song <muchun.song@...ux.dev>, linux-mm@...ck.org,
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Meta kernel team <kernel-team@...a.com>
Subject: Re: [PATCH] memcg: vmalloc: simplify MEMCG_VMALLOC updates

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@...ux.dev>
> ---
>  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?

Yes, the comment is clear, but git blame/log takes time.

Reviewed-by: Uladzislau Rezki (Sony) <urezki@...il.com>

--
Uladzislau Rezki