Re: [patch 4/8] mm: memcg: lookup_page_cgroup (almost) never returnsNULL

[Johannes Weiner]

On Mon, Nov 28, 2011 at 12:33:31PM +0530, Balbir Singh wrote:
> On Wed, Nov 23, 2011 at 9:12 PM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
> > From: Johannes Weiner <jweiner@xxxxxxxxxx>
> >
> > Pages have their corresponding page_cgroup descriptors set up before
> > they are used in userspace, and thus managed by a memory cgroup.
> >
> > The only time where lookup_page_cgroup() can return NULL is in the
> > page sanity checking code that executes while feeding pages into the
> > page allocator for the first time.
> >
> 
> This is a legacy check from the days when we allocated PC during fault
> time on demand. It might make sense to assert on !pc in DEBUG_VM mode
> at some point in the future

I don't think a BUG_ON bears more information than a null-pointer
dereference.
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