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

[Andrew Morton <akpm@linux-foundation.org>]

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.

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.

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