On Mon, Nov 28, 2011 at 12:33:31PM +0530, Balbir Singh wrote:

On Wed, Nov 23, 2011 at 9:12 PM, Johannes Weiner [off-list ref] wrote:

quoted

From: Johannes Weiner <redacted>

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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