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    snmp: reduce percpu needs by 50% · 8f0ea0fe
    Eric Dumazet 提交于
    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 be281e55 (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: NEric Dumazet <eric.dumazet@gmail.com>
    CC: Andi Kleen <andi@firstfloor.org>
    CC: Ingo Molnar <mingo@elte.hu>
    CC: Tejun Heo <tj@kernel.org>
    CC: Christoph Lameter <cl@linux-foundation.org>
    CC: Benjamin Herrenschmidt <benh@kernel.crashing.org
    CC: linux-arch@vger.kernel.org
    Signed-off-by: NDavid S. Miller <davem@davemloft.net>
    8f0ea0fe
af_inet.c 42.4 KB