On Tue, 17 May 2011 11:24:40 -0700 (PDT)
Hugh Dickins <hughd@xxxxxxxxxx> 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,
so I think counting vm events of the memcg is right.
Thanks,
Daisuke Nishimura.
> We don't know the target mm in shmem_getpage(), so do it at the outer
> level in shmem_fault(); and it's easier to follow if we move the
> count_vm_event(PGMAJFAULT) there too.
>
> Hah, it was using __count_vm_event() before, sneaking that update into
> the unpreemptible section under info->lock: well, it comes to the same
> on x86 at least, and I still think it's best to keep these together.
>
> Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
> ---
>
> mm/shmem.c | 13 ++++++-------
> 1 file changed, 6 insertions(+), 7 deletions(-)
>
> --- mmotm/mm/shmem.c 2011-05-13 14:57:45.367884578 -0700
> +++ linux/mm/shmem.c 2011-05-17 10:27:19.901934756 -0700
> @@ -1293,14 +1293,10 @@ repeat:
> swappage = lookup_swap_cache(swap);
> if (!swappage) {
> shmem_swp_unmap(entry);
> + spin_unlock(&info->lock);
> /* here we actually do the io */
> - if (type && !(*type & VM_FAULT_MAJOR)) {
> - __count_vm_event(PGMAJFAULT);
> - mem_cgroup_count_vm_event(current->mm,
> - PGMAJFAULT);
> + if (type)
> *type |= VM_FAULT_MAJOR;
> - }
> - spin_unlock(&info->lock);
> swappage = shmem_swapin(swap, gfp, info, idx);
> if (!swappage) {
> spin_lock(&info->lock);
> @@ -1539,7 +1535,10 @@ static int shmem_fault(struct vm_area_st
> error = shmem_getpage(inode, vmf->pgoff, &vmf->page, SGP_CACHE, &ret);
> if (error)
> return ((error == -ENOMEM) ? VM_FAULT_OOM : VM_FAULT_SIGBUS);
> -
> + if (ret & VM_FAULT_MAJOR) {
> + count_vm_event(PGMAJFAULT);
> + mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
> + }
> return ret | VM_FAULT_LOCKED;
> }
>
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