Re: [PATCH 08/25] Calculate the preferred zone for allocation only once

Pekka Enberg
2009-04-21T08:28:52Z

On Tue, 2009-04-21 at 09:27 +0100, Mel Gorman wrote:
> > You might want to add an explanation to the changelog why this change is
> > safe. It looked like a functional change at first glance and it was
> > pretty difficult to convince myself that __alloc_pages_slowpath() will
> > always return NULL when there's no preferred zone because of the other
> > cleanups in this patch series.
> >
>
> Is this better?
>
> get_page_from_freelist() can be called multiple times for an allocation.
> Part of this calculates the preferred_zone which is the first usable zone in
> the zonelist but the zone depends on the GFP flags specified at the beginning
> of the allocation call. This patch calculates preferred_zone once. It's safe
> to do this because if preferred_zone is NULL at the start of the call, no
> amount of direct reclaim or other actions will change the fact the allocation
> will fail.

Perfect!