Re: [RFC][PATCH] lib: generic percpu counter array

From: Christoph Lameter
Date: Thu Nov 05 2009 - 15:04:24 EST

On Thu, 5 Nov 2009, KAMEZAWA Hiroyuki wrote:

> Anothter major percpu coutner is vm_stat[]. This patch implements
> vm_stat[] style counter array in lib/percpu_counter.c
> This is designed for introducing vm_stat[] style counter to memcg,
> but maybe useful for other people. By using this, counter array
> using percpu can be implemented easily in compact structure.

Note that vm_stat support was written that way because we have extreme
space constraints due to the need to keep statistics per zone and per cpu
and avoid cache line pressure that would result through the use of big
integer arrays per zone and per cpu. For a large number of zones and cpus
this is desastrous.

If you only need to keep statistics per cpu for an entity then the vmstat
approach is overkill. A per cpu allocation of a counter is enough.

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