linux-kernel - Re: [PATCH 20/20] Get rid of the concept of hot/cold page freeing

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Date:	Tue, 24 Feb 2009 16:01:03 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
Cc:	linux-mm@...ck.org, penberg@...helsinki.fi, riel@...hat.com,
	kosaki.motohiro@...fujitsu.com, cl@...ux-foundation.org,
	hannes@...xchg.org, npiggin@...e.de, linux-kernel@...r.kernel.org,
	ming.m.lin@...el.com, yanmin_zhang@...ux.intel.com
Subject: Re: [PATCH 20/20] Get rid of the concept of hot/cold page freeing

On Tue, 24 Feb 2009 11:51:26 +0000
Mel Gorman <mel@....ul.ie> wrote:

> > > Almost the opposite with steady improvements almost all the way through.
> > > 
> > > With the patch applied, we are still using hot/cold information on the
> > > allocation side so I'm somewhat surprised the patch even makes much of a
> > > difference. I'd have expected the pages being freed to be mostly hot.
> > 
> > Oh yeah.  Back in the ancient days, hot-cold-pages was using separate
> > magazines for hot and cold pages.  Then Christoph went and mucked with
> > it, using a single queue.  That might have affected things.
> > 
> 
> It might have. The impact is that requests for cold pages can get hot pages
> if there are not enough cold pages in the queue so readahead could prevent
> an active process getting cache hot pages. I don't think that would have
> showed up in the microbenchmark though.

We switched to doing non-temporal stores in copy_from_user(), didn't
we?  That would rub out the benefit which that microbenchmark
demonstrated?

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