linux-kernel - Re: [PATCH] perf: Better fit max unprivileged mlock pages for tools needs

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Date:	Wed, 23 Mar 2011 15:38:12 -0300
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Han Pingtian <phan@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>,
	Stephane Eranian <eranian@...gle.com>,
	Stable <stable@...nel.org>
Subject: Re: [PATCH] perf: Better fit max unprivileged mlock pages for
	tools needs

Em Wed, Mar 23, 2011 at 07:29:39PM +0100, Frederic Weisbecker escreveu:
> The maximum kilobytes of locked memory that an unprivileged user can
> reserve is of 512 kB = 128 pages by default, scaled to the number of
> onlined CPUs, which fits well with the tools that use 128 data pages
> by default.
> 
> However tools actually use 129 pages, because they need one more for
> the user control page. Thus the default mlock threshold is not
> sufficient for the default tools needs and we always end up to
> evaluate the constant mlock rlimit policy, which doesn't have this
> scaling with the number of online CPUs.
> 
> Hence, on systems that have more than 16 CPUs, we overlap the rlimit
> threshold and fail to mmap:
> 
> 	$ perf record ls
> 	Error: failed to mmap with 1 (Operation not permitted)
> 
> Just increase the max unprivileged mlock threshold by one page so
> that it supports well perf tools even after 16 CPUs.

Thanks!

Acked-by: Arnaldo Carvalho de Melo <acme@...hat.com>
 
> Reported-by: Han Pingtian <phan@...hat.com>
> Reported-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Reported-by: Arnaldo Carvalho de Melo <acme@...hat.com>
> Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Stephane Eranian <eranian@...gle.com>
> Cc: Stable <stable@...nel.org>
> ---
>  kernel/perf_event.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/kernel/perf_event.c b/kernel/perf_event.c
> index 3472bb1..d5943b0 100644
> --- a/kernel/perf_event.c
> +++ b/kernel/perf_event.c
> @@ -145,7 +145,8 @@ static struct srcu_struct pmus_srcu;
>   */
>  int sysctl_perf_event_paranoid __read_mostly = 1;
>  
> -int sysctl_perf_event_mlock __read_mostly = 512; /* 'free' kb per user */
> +/* Minimum for 128 pages + 1 for the user control page */
> +int sysctl_perf_event_mlock __read_mostly = 516; /* 'free' kb per user */
>  
>  /*
>   * max perf event sample rate
> -- 
> 1.7.3.2
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