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Subject: Re: [PATCH] perf_events: improve DS/BTS/PEBS buffer allocation
From: Peter Zijlstra <peterz@infradead.org>
To: Stephane Eranian <eranian@google.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        linux-kernel@vger.kernel.org, mingo@elte.hu, paulus@samba.org,
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        "markus.t.metzger" <markus.t.metzger@intel.com>
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Date: Mon, 13 Sep 2010 17:41:16 +0200
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On Mon, 2010-09-13 at 17:31 +0200, Stephane Eranian wrote:
> On Mon, Sep 13, 2010 at 5:24 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> > On Mon, 2010-09-13 at 17:20 +0200, Stephane Eranian wrote:
> >
> >> That is the case we the sizes you have chosen today. For DS, we
> >> could round up to one page for now.
> >
> > Markus chose the BTS size, for PEBS a single page was plenty since we do
> > single event things (although we could do multiple for attr.precise_ip <
> > 2).
> >
> > For DS there's:
> >  kmalloc_node(sizeof(struct ds), GFP_KERNEL | __GFP_ZERO, cpu_node(cpu));
> >
> Ok, let try again with alloc_pages_node() + kmalloc_node().
> I think we can stick with kmalloc() for DS because we are far from
> consuming a page.

Thing is, if you're really seeing allocation failures,
alloc_pages_node() isn't going to help. And the problem is, these
allocations aren't movable, so memory compaction and all the other fancy
stuff aren't really going to help much :/

There was some talk about a function that should sync all of vmalloc
space, but iirc it was broken for some configs.