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Subject: Re: [PATCH] perf_events: improve DS/BTS/PEBS buffer allocation
From: Peter Zijlstra <peterz@infradead.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: eranian@google.com, linux-kernel@vger.kernel.org, mingo@elte.hu,
        paulus@samba.org, davem@davemloft.net, fweisbec@gmail.com,
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Date: Mon, 13 Sep 2010 21:49:20 +0200
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On Mon, 2010-09-13 at 21:35 +0200, Andi Kleen wrote:
> Stephane Eranian <eranian@google.com> writes:
> 
> > The DS, BTS, and PEBS memory regions were allocated using kzalloc(), i.e.,
> > requesting contiguous physical memory. There is no such restriction on
> > DS, PEBS and BTS buffers. Using kzalloc() could lead to error in case
> > no contiguous physical memory is available. BTS is requesting 64KB,
> > thus it can cause issues. PEBS is currently only requesting one page.
> > Both PEBS and BTS are static buffers allocated for each CPU at the
> > first user. When the last user exists, the buffers are released.
> 
> DS supports page tables, but I have some doubts it really 
> supports page faults. vmalloc today does page faults. 
> 
> I think the change is a good idea, but it will need vmalloc_sync_all()
> everywhere.

Right, I seem to remember from that last discussion on vmalloc vs NMI
that vmalloc_sync_all() had some issues, or am I totally mis-remembering
that?

But yes, a vmalloc_sync_all() after the vmalloc_node() and this should
indeed work.