linux-kernel - Re: [patch 01/28] cpu alloc: The allocator

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Message-ID: <473A1DEA.7000307@cosmosbay.com>
Date:	Tue, 13 Nov 2007 22:58:02 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Christoph Lameter <clameter@....com>
CC:	David Miller <davem@...emloft.net>, akpm@...ux-foundation.org,
	linux-mm@...r.kernel.org, linux-kernel@...r.kernel.org,
	schwidefsky@...ibm.com
Subject: Re: [patch 01/28] cpu alloc: The allocator

Christoph Lameter a écrit :
> On Tue, 13 Nov 2007, David Miller wrote:
> 
>> One thing you could do is simply use a vmalloc allocation in the
>> non-virtualized case.
> 
> Yuck. Meaning to add more crappy code. The bss limitations to 8M is a bit 
> strange though. Do other platforms have the same issues? 

Maybe not so crappy, because even for i386 code, you might use not a strict 
vmalloc() implementation but at least reserving percpu space inside the 
vmalloc range. (ie not use a dedicated area as your current patchset does)

This is because NR_CPUS is defaulted to 32 on i386 (with a limit of 256), so 
reserving 256*256KB = 64 MB of virtual space might be too much. (this is half 
the typical vmalloc area)

The idea would be :

- Reserving an area of NR_CPUS*256KB inside vmalloc() space (but of course not 
allocating pages)

- Then for each non possible cpu, 'release' its 256KB area and give it back to 
vmalloc free areas pool.

Once you add in mm/vmalloc.c all needed helpers, no need to use BSS Megablob 
anymore ?
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