Re: [rfc] [patch] mm: zone_reclaim fix for pseudo file systems

Christoph Lameter
2007-07-31T02:01:07Z

On Mon, 30 Jul 2007, Ravikiran G Thirumalai wrote:

> On Mon, Jul 30, 2007 at 05:27:41PM -0700, Christoph Lameter wrote:
> >On Mon, 30 Jul 2007, Andrew Morton wrote:
> >
> >> The problem is that __zone_reclaim() doesn't use all_unreclaimable at all.
> >> You'll note that all the other callers of shrink_zone() do take avoiding
> >> action if the zone is in all_unreclaimable state, but __zone_reclaim() forgot
> >> to.
> >
> >zone reclaim only runs if there are unmapped file backed pages that can be
> >reclaimed.
>
> Yes, and in this case, without the patch, VM considers RAMFS pages to be
> file backed, thus being fooled into entering reclaim. The process entering
> into reclaim in our tests gets in through zone_reclaim.

That means RAMFS pages are accounted as NR_FILE_PAGES but not as
NR_FILE_MAPPED..... So we have unmapped pages that are not reclaimable.

But they are not really file backed pages. They are backed by memory. Can
we just not increment NR_FILE_MAPPED? Should they not be accounted for an
NR_ANON_PAGES or so?