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

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Date:	Wed, 27 Feb 2008 10:05:04 +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
Subject: Re: [PATCH 00/28] Swap over NFS -v16

Hi Peter,

On Wed, Feb 27, 2008 at 9:58 AM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
>  > 1/ I note there is no way to tell if memory returned by kmalloc is
>  >   from the emergency reserve - which contrasts with alloc_page
>  >   which does make that information available through page->reserve.
>  >   This seems a slightly unfortunate aspect of the interface.
>
>  Yes, but alas there is no room to store such information in kmalloc().
>  That is, in a sane way. I think it was Daniel Phillips who suggested
>  encoding it in the return pointer by flipping the low bit - but that is
>  just too ugly and breaks all current kmalloc sites to boot.

Why can't you add a kmem_is_emergency() to SLUB that looks up the
cache/slab/page (whatever is the smallest unit of the emergency pool
here) for the object and use that?
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