Re: [PATCH 2/4] mm, procfs: account for shmem swap in /proc/pid/smaps

[Konstantin Khlebnikov]

On 11.03.2015 18:26, Jerome Marchand wrote:
> On 03/11/2015 04:03 PM, Konstantin Khlebnikov wrote:
> > On 11.03.2015 15:30, Konstantin Khlebnikov wrote:
> > > On Thu, Feb 26, 2015 at 4:51 PM, Vlastimil Babka <vbabka@xxxxxxx> wrote:
> > > > Currently, /proc/pid/smaps will always show "Swap: 0 kB" for
> > > > shmem-backed
> > > > mappings, even if the mapped portion does contain pages that were
> > > > swapped out.
> > > > This is because unlike private anonymous mappings, shmem does not
> > > > change pte
> > > > to swap entry, but pte_none when swapping the page out. In the smaps
> > > > page
> > > > walk, such page thus looks like it was never faulted in.
> > >
> > > Maybe just add count of swap entries allocated by mapped shmem into
> > > swap usage of this vma? That's isn't exactly correct for partially
> > > mapped shmem but this is something weird anyway.
> >
> > Something like that (see patch in attachment)
>
> -8<---
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index cf2d0ca010bc..492f78f51fc2 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1363,6 +1363,13 @@ static struct mempolicy *shmem_get_policy(struct
> vm_area_struct *vma,
>   }
>   #endif
>
> +static unsigned long shmem_get_swap_usage(struct vm_area_struct *vma)
> +{
> +	struct inode *inode = file_inode(vma->vm_file);
> +
> +	return SHMEM_I(inode)->swapped;
> +}
> +
>   int shmem_lock(struct file *file, int lock, struct user_struct *user)
>   {
>   	struct inode *inode = file_inode(file);
>
> -8<---
>
> That will not work for shared anonymous mapping since they all share the
> same vm_file (/dev/zero).

Nope. They have different files and inodes.
They're just called "/dev/zero (deleted)".

> Jerome


--
Konstantin
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