Re: [PATCH] Hugetlb pages rss accounting is incorrect in /proc/<pid>/smaps

[Michal Hocko]

[CCing Naoya]

On Tue 24-10-17 16:56:08, Prakash Sangappa wrote:
> Resident set size(Rss) accounting of hugetlb pages is not done
> currently in /proc/<pid>/smaps. The pmap command reads rss from
> this file and so it shows Rss to be 0 in pmap -x output for
> hugetlb mapped vmas. This patch fixes it.

We do not account in rss because we do have a dedicated counters
depending on whether the hugetlb page is mapped privately or it is
shared. The reason this is not in RSS IIRC is that a large unexpected
RSS from hugetlb pages might confuse system monitors. This is one of
those backward compatibility issues when you start accounting something
too late.

> Signed-off-by: Prakash Sangappa <prakash.sangappa@xxxxxxxxxx>
> ---
>  fs/proc/task_mmu.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 5589b4b..c7e1048 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -724,6 +724,7 @@ static int smaps_hugetlb_range(pte_t *pte, unsigned long hmask,
>  			mss->shared_hugetlb += huge_page_size(hstate_vma(vma));
>  		else
>  			mss->private_hugetlb += huge_page_size(hstate_vma(vma));
> +		mss->resident += huge_page_size(hstate_vma(vma));
>  	}
>  	return 0;
>  }
> -- 
> 2.7.4
> 

-- 
Michal Hocko
SUSE Labs