Message-ID: <43DAAAE3.2030107@cosmosbay.com>
Date: Sat, 28 Jan 2006 00:21:07 +0100
From: Eric Dumazet <dada1@cosmosbay.com>
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To: Ravikiran G Thirumalai <kiran@scalex86.org>
Cc: Andrew Morton <akpm@osdl.org>, davem@davemloft.net,
       linux-kernel@vger.kernel.org, shai@scalex86.org, netdev@vger.kernel.org,
       pravins@calsoftinc.com
Subject: Re: [patch 3/4] net: Percpufy frequently used variables -- proto.sockets_allocated
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Ravikiran G Thirumalai a ?crit :
> On Fri, Jan 27, 2006 at 11:30:23PM +0100, Eric Dumazet wrote:
>> There are several issues here :
>>
>> alloc_percpu() current implementation is a a waste of ram. (because it uses 
>> slab allocations that have a minimum size of 32 bytes)
> 
> Oh there was a solution for that :).  
> 
> http://lwn.net/Articles/119532/
> 
> I can quickly revive it if there is interest.
> 

Well, nice work ! :)

Maybe a litle bit complicated if expected percpu space is 50 KB per cpu ?

Why not use a boot time allocated percpu area (as done today in 
setup_per_cpu_areas()), but instead of reserving extra space for module's 
percpu data, being able to serve alloc_percpu() from this reserved area (ie no 
kmalloced data anymore), and keeping your

#define per_cpu_ptr(ptr, cpu)  ((__typeof__(ptr))         \
	(RELOC_HIDE(ptr,  PCPU_BLKSIZE * cpu)))

Some code from kernel/module.c could be reworked to serve both as an allocator 
when a module percpudata must be relocated (insmod)/freed (rmmod), and serve 
alloc_percpu() for 'dynamic allocations'

Eric
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