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SubjectRe: [PATCH mmotm/next] mm: memcontrol: rewrite charge API: fix shmem_unuse
On Mon, 30 Jun 2014 17:10:54 -0700 (PDT) Hugh Dickins <hughd@google.com> wrote:

> On Mon, 30 Jun 2014, Andrew Morton wrote:
> > On Mon, 30 Jun 2014 15:48:39 -0700 (PDT) Hugh Dickins <hughd@google.com> wrote:
> > > - return 0;
> > > + return -EAGAIN;
> >
> > Maybe it's time to document the shmem_unuse_inode() return values.
>
> Oh dear. I had hoped they would look after themselves. This one is a
> private matter between shmem_unuse_inode and its one caller, just below.

Well, readers of shmem_unuse_inode() won't know that unless we tell them.


> > > + if (error) {
> > > + if (error != -ENOMEM)
> > > + error = 0;
> > > mem_cgroup_cancel_charge(page, memcg);
> > > } else
> > > mem_cgroup_commit_charge(page, memcg, true);
> >
> > If I'm reading this correctly, shmem_unuse() can now return -EAGAIN and
> > that can get all the way back to userspace. `man 2 swapoff' doesn't
> > know this...
>
> if (error) {
> if (error != -ENOMEM)
> error = 0;
> ...
> return error;
>
> So the only values returned from shmem_unuse_inode() to its caller
> try_to_unuse() are 0 and -ENOMEM. Those may get passed back to the
> user, but -EAGAIN was just an internal shmem.c detail.

OK.


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