Re: [PATCH] memcg: clean up migration

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

> >> @@ -678,13 +675,11 @@ static int unmap_and_move(new_page_t get_new_page, unsigned long private,
> >> A  A  A  }
> >>
> >> A  A  A  /* charge against new page */
> >> - A  A  charge = mem_cgroup_prepare_migration(page, newpage, &mem, GFP_KERNEL);
> >> - A  A  if (charge == -ENOMEM) {
> >> - A  A  A  A  A  A  rc = -ENOMEM;
> >> + A  A  rc = mem_cgroup_prepare_migration(page, newpage, &mem, GFP_KERNEL);
> >> + A  A  if (rc)
> >> A  A  A  A  A  A  A  goto unlock;
> >> - A  A  }
> >> - A  A  BUG_ON(charge);
> >>
> >> + A  A  rc = -EAGAIN;
> >> A  A  A  if (PageWriteback(page)) {
> >> A  A  A  A  A  A  A  if (!force || !sync)
> >> A  A  A  A  A  A  A  A  A  A  A  goto uncharge;
> > How about
> >
> > A  A  A  A if (mem_cgroup_prepare_migration(..)) {
> > A  A  A  A  A  A  A  A rc = -ENOMEM;
> > A  A  A  A  A  A  A  A goto unlock;
> > A  A  A  A }
> >
> > ?
> >
> > Re-setting "rc" to -EAGAIN is not necessary in this case.
> > "if (mem_cgroup_...)" is commonly used in many places.
> >
> It works now but Johannes doesn't like it and me, either.
> It makes unnecessary dependency which mem_cgroup_preparre_migration
> can't propagate error to migrate_pages.
> Although we don't need it, I want to remove such unnecessary dependency.
> 
I see.
Thank you for your explanation.

Daisuke Nishimura.

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