linux-kernel - Re: [PATCH v0 1/2] perf: Add an option to ask for high order allocations for AUX buffers

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Date:   Wed, 13 Feb 2019 18:54:34 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Arnaldo Carvalho de Melo <acme@...hat.com>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        jolsa@...hat.com
Subject: Re: [PATCH v0 1/2] perf: Add an option to ask for high order
 allocations for AUX buffers

On Wed, Feb 13, 2019 at 05:47:56PM +0000, Mel Gorman wrote:
> If there is a tangiable performance benefit from using contiguous regions
> then I would suggest optimistically allocating them with appropriate
> GFP flags to avoid large latencies at startup time and fall back if
> necessary. 

Right; the code does the fallback thing. It successively tries smaller
order allocations until 0-order fails.

It currently uses:

#define PERF_AUX_GFP    (GFP_KERNEL | __GFP_ZERO | __GFP_NOWARN | __GFP_NORETRY)

Is that what you could consider appropriate?