Re: [PATCH 2/2] Helping prezoring with reduced fragmentation allocation

[Mel Gorman <mel@csn.ul.ie>]

On Tue, 1 Feb 2005, Christoph Lameter wrote:

> On Tue, 1 Feb 2005, Mel Gorman wrote:
>
> > > Would it not be better to zero the global 2^MAX_ORDER pages by the scrub
> > > daemon and have a global zeroed page list? That way you may avoid zeroing
> > > when splitting pages?
> > >
> >
> > Maybe, but right now when there are no 2^MAX_ORDER pages, the scrub daemon
> > is going to be doing nothing which is why I think it needs to look at the
> > free pages of lower orders.
> >
> > That is solveable though in one of two ways. One, the scrub daemon can
> > zero pages from the global list and then add them to the USERZERO pool. It
> > has the advantage of requiring no more memory and is simple. The second is
> > to create a second global list. However, I think it only makes sense to
> > have this as part of the scrub daemon patch (I can write it if thats a
> > problem) rather than a standalone patch from me.
>
> Approach one is fine and I will do an update the remaining prezero patches
> to do just that.

There is another problem with approach one. Assuming all 2^MAX_ORDER pages
have been zeroed and in USERZERO pool and there are no other free pages,
an allocation for the USERRCLM pool would search all the other pools
before finding the zerod pages. This could really slow things up but it is
not a problem approach two suffers from.

> When will your patches be in Linus tree? ;-)
>

Your guess is as good as mine :) . I am fairly sure the allocator is
somewhere in Andrew's list of patches to look at to consider for inclusion
into -mm so I suppose it'll get a spin in that tree when he feels it's
ready.

-- 
Mel Gorman
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