linux-kernel - Re: [13/14] vcompound: Use vcompound for swap

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Message-ID: <20080325075236.GG2170@one.firstfloor.org>
Date:	Tue, 25 Mar 2008 08:52:36 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Christoph Lameter <clameter@....com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [13/14] vcompound: Use vcompound for swap_map

On Mon, Mar 24, 2008 at 12:54:54PM -0700, Christoph Lameter wrote:
> On Fri, 21 Mar 2008, Andi Kleen wrote:
> 
> > But I used a simple trick to avoid the waste problem: it allocated a
> > continuous range rounded up to the next page-size order and then freed
> > the excess pages back into the page allocator. That was called
> > alloc_exact(). If you replace vmalloc with alloc_pages you should
> > use something like that too I think.
> 
> One way of dealing with it would be to define an additional allocation 
> variant that allows the limiting of the loss? I noted that both the swap
> and the wait tables vary significantly between allocations. So we could 
> specify an upper boundary of a loss that is acceptable. If too much memory
> would be lost then use vmalloc unconditionally.

I liked your idea of fixing compound pages to not rely on order
better. Ok it is likely more work to implement @)

Also if anything preserving memory should be default, but maybe
skippable a with __GFP_GO_FAST flag.

-Andi
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