Re: [PATCH mmotm] add the pagefault count into memcg stats: shmem fix

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

On Wed, 18 May 2011 11:25:48 -0700 (PDT)
Hugh Dickins <hughd@google.com> wrote:

> On Wed, 18 May 2011, Daisuke Nishimura wrote:
> > On Tue, 17 May 2011 11:24:40 -0700 (PDT)
> > Hugh Dickins <hughd@google.com> wrote:
> > 
> > > mem_cgroup_count_vm_event() should update the PGMAJFAULT count for the
> > > target mm, not for current mm (but of course they're usually the same).
> > > 
> > hmm, why ?
> > In shmem_getpage(), we charge the page to the memcg where current mm belongs to,
> 
> (In the case when it's this fault which is creating the page.
> Just as when filemap_fault() reads in the page, add_to_page_cache
> will charge it to the current->mm's memcg, yes.  Arguably correct.)
> 
> > so I think counting vm events of the memcg is right.
> 
> It should be consistent with which task gets the maj_flt++, and
> it should be consistent with filemap_fault(), and it should be a
> subset of what's counted by mem_cgroup_count_vm_event(mm, PGFAULT).
> 
> In each case, those work on target mm rather than current->mm.
> 
Thank you for your explanation. I can agree that we should count PGMAJFLT of memcg
where the target mm belongs to.

Thanks,
Daisuke Nishimura.

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