Re: [PATCH 0/8] Avoiding fragmentation with subzone groupings v25

[Mel Gorman]

On Fri, 8 Sep 2006, Peter Zijlstra wrote:

> On Thu, 2006-09-07 at 17:58 -0700, Andrew Morton wrote:
> > On Thu,  7 Sep 2006 20:03:42 +0100 (IST)
> > Mel Gorman <mel@xxxxxxxxx> wrote:
> >
> > > When a page is allocated, the page-flags
> > > are updated with a value indicating it's type of reclaimability so that it
> > > is placed on the correct list on free.
> >
> > We're getting awful tight on page-flags.
> >
> > Would it be possible to avoid adding the flag?  Say, have a per-zone bitmap
> > of size (zone->present_pages/(1<<MAX_ORDER)) bits, then do a lookup in
> > there to work out whether a particular page is within a MAX_ORDER clump of
> > easy-reclaimable pages?
>
> That would not actually work, the fallback allocation path can move
> blocks smaller than MAX_ORDER to another recaim type.

Believe it or not, it may be desirably to have a whole block represented 
by one or two bits. If a fallback allocation occurs and I move blocks 
between lists, I want pages that free later to be freed to the new list as 
well. Currently that doesn't happen because the flags are set per-page but 
it used to happen in an early version of anti-frag.

> But yeah, page flags are getting right, perhaps Rafael can use his
> recently introduced bitmaps to rid us of the swsusp flags?

--
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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