Re: [PATCH] Page allocator: Get rid of the list of cold pages

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

On (21/11/07 15:23), Andrew Morton didst pronounce:
> On Wed, 21 Nov 2007 22:20:59 +0000
> Mel Gorman <mel@csn.ul.ie> wrote:
> 
> > I cannot see the evidence of this 3x improvement around the 32K filesize
> > mark. It may be because my test is very different to what happened before,
> > I got something wrong or the per-CPU allocator is not as good as it used to
> > be and does not give out the same hot-pages all the time.
> 
> Could be that when you return a handful of pages to the page allocator
> and then allocate a handful of pages, you get the same pages back.  But
> that the page allocator wasn't doing that 4-5 years ago when that code
> went in.
> 

Maybe.

> Of course, even if the page allocator is indeed doing this for us, you'd
> still expect to see benefits from the per-cpu magazines when each CPU is
> allocating and freeing a number of pages which is close to the size of
> that CPU's L1 cache.  Because when the pages are going into and coming from
> a shared-by-all-cpus pool, each CPU will often get pages which are hot in
> a different cpu's L1.
> 

I checked and I am not seeing any clear benefit around the size of the L1
cache (64K D-cache). It could be because the granularity of the time is
too low and the cost of zeroing the page is drowning everything else
out in this test.

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

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