Re: [patch] x86, perf: avoid spamming kernel log for bts buffer failure

[Peter Zijlstra]

On Mon, Jun 30, 2014 at 04:04:08PM -0700, David Rientjes wrote:
> It's unnecessary to excessively spam the kernel log anytime the BTS buffer 
> cannot be allocated, so make this allocation __GFP_NOWARN.
> 
> The user probably will want to at least find some artifact that the 
> allocation has failed in the past, probably due to fragmentation because 
> of its large size, when it's not allocated at bootstrap.  Thus, add a 
> WARN_ONCE() so something is left behind for them to understand why perf 
> commnads that require PEBS is not working properly.

Can you elaborate a bit under which conditions this triggered? Typically
we should be doing fairly well allocating such buffers with GFP_KERNEL,
that should allow things like compaction to run and create higher order
pages.

And the BTS (branch trace store) isn't _that_ large.

That said, the patch is reasonable; although arguably we should maybe do
the same to alloc_pebs_buffer().

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