linux-kernel - Re: [PATCH net-next-2.6] snmp: reduce percpu needs by 50%

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Message-Id: <20110611.162416.414198854514319441.davem@davemloft.net>
Date:	Sat, 11 Jun 2011 16:24:16 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org, andi@...stfloor.org,
	linux-kernel@...r.kernel.org, benh@...nel.crashing.org,
	mingo@...e.hu, tj@...nel.org, cl@...ux-foundation.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH net-next-2.6] snmp: reduce percpu needs by 50%

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Sat, 11 Jun 2011 07:45:51 +0200

> SNMP mibs use two percpu arrays, one used in BH context, another in USER
> context. With increasing number of cpus in machines, and fact that ipv6
> uses per network device ipstats_mib, this is consuming a lot of memory
> if many network devices are registered.
> 
> commit be281e554e2a (ipv6: reduce per device ICMP mib sizes) shrinked
> percpu needs for ipv6, but we can reduce memory use a bit more.
> 
> With recent percpu infrastructure (irqsafe_cpu_inc() ...), we no longer
> need this BH/USER separation since we can update counters in a single
> x86 instruction, regardless of the BH/USER context.
> 
> Other arches than x86 might need to disable irq in their
> irqsafe_cpu_inc() implementation : If this happens to be a problem, we
> can make SNMP_ARRAY_SZ arch dependent, but a previous poll
> ( https://lkml.org/lkml/2011/3/17/174 ) to arch maintainers did not
> raise strong opposition.
> 
> Only on 32bit arches, we need to disable BH for 64bit counters updates
> done from USER context (currently used for IP MIB)
> 
> This also reduces vmlinux size :
> 
> 1) x86_64 build
> $ size vmlinux.before vmlinux.after
>    text	   data	    bss	    dec	    hex	filename
> 7853650	1293772	1896448	11043870	 a8841e	vmlinux.before
> 7850578	1293772	1896448	11040798	 a8781e	vmlinux.after
> 
> 2) i386  build
> $ size vmlinux.before vmlinux.afterpatch 
>    text	   data	    bss	    dec	    hex	filename
> 6039335	 635076	3670016	10344427	 9dd7eb	vmlinux.before
> 6037342	 635076	3670016	10342434	 9dd022	vmlinux.afterpatch
> 
> Signed-off-by: Eric Dumazet <eric.dumazet@...il.com>

Looks good to me, applied, thanks Eric.
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