Re: [PATCH 1/4] compcache: xvmalloc memory allocator

From: Nitin Gupta <ngupta@vflare.org>
To: Christoph Lameter <cl@linux-foundation.org>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>,
	Pekka Enberg <penberg@cs.helsinki.fi>,
	akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linux-mm-cc@laptop.org
Subject: Re: [PATCH 1/4] compcache: xvmalloc memory allocator
Date: Wed, 26 Aug 2009 21:47:46 +0530	[thread overview]
Message-ID: <4A95602A.5040109@vflare.org> (raw)
In-Reply-To: <alpine.DEB.1.10.0908261209240.9933@gentwo.org>

On 08/26/2009 09:40 PM, Christoph Lameter wrote:
> On Wed, 26 Aug 2009, Nitin Gupta wrote:
>
>> I went crazy. I meant 40 bits for PFN -- not 48. This 40-bit PFN should be
>> sufficient for all archs. For archs where 40 + PAGE_SHIFT<  MAX_PHYSMEM_BITS
>> ramzswap will just issue a compiler error.
>
> How about restricting the xvmalloc memory allocator to 32 bit? If I
> understand correctly xvmalloc main use in on 32 bit in order to be
> able to use HIGHMEM?
>
>

I have just replaced all PFN usage with struct page in xvmalloc.

The main use of xvmalloc is not just the use of HIGHMEM -- its just one
of the things. Other reasons are:
  - O(1) alloc/free
  - Low fragmentation
  - Allocates 0-order pages to expand pools

Following gives more information:
http://code.google.com/p/compcache/wiki/xvMalloc
http://code.google.com/p/compcache/wiki/xvMallocPerformance

Thanks,
Nitin