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

[Hugh Dickins <hughd@google.com>]

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.

Hugh

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