linux-kernel - Re: [RFC PATCH 1/2] perf_events: add support for per-cpu per-cgroup monitoring (v3)

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Message-ID: <1284106566.402.26.camel@laptop>
Date:	Fri, 10 Sep 2010 10:16:06 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, paulus@...ba.org,
	davem@...emloft.net, fweisbec@...il.com,
	perfmon2-devel@...ts.sf.net, eranian@...il.com,
	robert.richter@....com, acme@...hat.com, Tejun Heo <tj@...nel.org>
Subject: Re: [RFC PATCH 1/2] perf_events: add support for per-cpu
 per-cgroup monitoring (v3)

On Thu, 2010-09-09 at 23:41 +0200, Stephane Eranian wrote:
> > alloc_percpu() is zalloc_percpu() in fact, memory is already cleared.
> >
> I remember thinking about this and trying to trace to the code down
> to figure this out. But it is rather complicated. If alloc_percpu() always
> clears the memory, then I think that calling is zalloc_percpu()
> would be more helpful.... 

pcpu_populate_chunk() in mm/percpu-vm.c does indeed do that memset, the
one in mm/percpu-km.c does not.

It is not obviously clear to me the -km allocator does indeed result in
zero filled memory.

Tejun?
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