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

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Message-ID: <alpine.DEB.1.10.0902261226370.26440@qirst.com>
Date:	Thu, 26 Feb 2009 12:30:45 -0500 (EST)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Mel Gorman <mel@....ul.ie>
cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	penberg@...helsinki.fi, riel@...hat.com,
	kosaki.motohiro@...fujitsu.com, 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 Thu, 26 Feb 2009, Mel Gorman wrote:

> > I tried the general use of a pool of zeroed pages back in 2005. Zeroing
> > made sense only if the code allocating the page did not immediately touch
> > the cachelines of the page.
>
> Any feeling as to how often this was the case?

Not often enough to justify the merging of my patches at the time. This
was publicly discussed on lkml:

http://lkml.indiana.edu/hypermail/linux/kernel/0503.2/0482.html

> Indeed, any gain if it existed would be avoiding zeroing the pages used
> by userspace. The cleanup would be reducing the amount of
> architecture-specific code.
>
> I reckon it's worth an investigate but there is still other lower-lying
> fruit.

I hope we can get rid of various ugly elements of the quicklists if the
page allocator would offer some sort of support. I would think that the
slow allocation and freeing behavior is also a factor that makes
quicklists advantageous. The quicklist page lists are simply a linked list
of pages and a page can simply be dequeued and used.


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