linux-kernel - Re: [PATCH 00/28] Swap over NFS -v16

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Date:	Fri, 29 Feb 2008 13:58:52 +0200
From:	"Pekka Enberg" <penberg@...helsinki.fi>
To:	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>
Cc:	"Neil Brown" <neilb@...e.de>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	netdev@...r.kernel.org, trond.myklebust@....uio.no,
	"Christoph Lameter" <clameter@....com>
Subject: Re: [PATCH 00/28] Swap over NFS -v16

Hi Peter,

On Fri, Feb 29, 2008 at 1:51 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
>  I made page->reserve into PG_emergency and made that bit stick for the
>  lifetime of that page allocation. I then made kmem_is_emergency() look
>  up the head page backing that allocation's slab and return
>  PageEmergency().

[snip]

On Fri, Feb 29, 2008 at 1:51 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
>  This is a stricter model than I had before, and has one ramification I'm
>  not entirely sure I like.
>
>  It means the page remains a reserve page throughout its lifetime, which
>  means the slab remains a reserve slab throughout its lifetime. Therefore
>  it may never be used for !reserve allocations. Which in turn generates
>  complexities for the partial list.

Hmm, so why don't we then clear the PG_emergency flag then and
allocate a new fresh page to the reserves?

On Fri, Feb 29, 2008 at 1:51 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
>  Does this sound like something I should pursuit? I feel it might
>  complicate the slab allocators too much..

I can't answer that question until I see the code ;-). But overall, I
think it's better to put that code in SLUB rather than trying to work
around it elsewhere. The fact is, as soon as you have some sort of
reservation for _objects_, you need help from the SLUB allocator.

                           Pekka
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