Re: [PATCH v4] mm: per-thread vma caching

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 03 Mar 2014 16:59:38 -0800 Davidlohr Bueso <davidlohr@hp.com> wrote:

> > >...
> > >
> > > +static bool vmacache_valid(struct mm_struct *mm)
> > > +{
> > > +	struct task_struct *curr = current;
> > > +
> > > +	if (mm != curr->mm)
> > > +		return false;
> > 
> > What's going on here?  Handling a task poking around in someone else's
> > mm?  I'm thinking "__access_remote_vm", but I don't know what you were
> > thinking ;) An explanatory comment would be revealing.
> 
> I don't understand the doubt here. Seems like a pretty obvious thing to
> check -- yes it's probably unlikely but we certainly don't want to be
> validating the cache on an mm that's not ours... or are you saying it's
> redundant??

Well it has to be here for a reason and I'm wondering that that reason
is.  If nobody comes here with a foreign mm then let's remove it.  Or
perhaps stick a WARN_ON_ONCE() in there to detect the unexpected.  If
there _is_ a real reason, let's write that down.

> And no, we don't want __access_remote_vm() here.

__access_remote_vm doesn't look at the vma cache, so scrub that
explanation.

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