linux-kernel - Re: [PATCH 04/10] mm, page_alloc: Remove unnecessary taking of a seqlock when cpusets are disabled

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.10.1508121714290.19264@chino.kir.corp.google.com>
Date:	Wed, 12 Aug 2015 17:16:50 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Mel Gorman <mgorman@...hsingularity.net>
cc:	Linux-MM <linux-mm@...ck.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Rik van Riel <riel@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Michal Hocko <mhocko@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/10] mm, page_alloc: Remove unnecessary taking of a
 seqlock when cpusets are disabled

On Wed, 12 Aug 2015, Mel Gorman wrote:

> There is a seqcounter that protects against spurious allocation failures
> when a task is changing the allowed nodes in a cpuset. There is no need
> to check the seqcounter until a cpuset exists.
> 
> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
> Acked-by: David Rientjes <rientjes@...gle.com>
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> ---
>  include/linux/cpuset.h | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
> index 1b357997cac5..6eb27cb480b7 100644
> --- a/include/linux/cpuset.h
> +++ b/include/linux/cpuset.h
> @@ -104,6 +104,9 @@ extern void cpuset_print_task_mems_allowed(struct task_struct *p);
>   */
>  static inline unsigned int read_mems_allowed_begin(void)
>  {
> +	if (!cpusets_enabled())
> +		return 0;
> +
>  	return read_seqcount_begin(&current->mems_allowed_seq);
>  }
>  
> @@ -115,6 +118,9 @@ static inline unsigned int read_mems_allowed_begin(void)
>   */
>  static inline bool read_mems_allowed_retry(unsigned int seq)
>  {
> +	if (!cpusets_enabled())
> +		return false;
> +
>  	return read_seqcount_retry(&current->mems_allowed_seq, seq);
>  }
>  

This patch is an obvious improvement, but I think it's also possible to 
change this to be

	if (nr_cpusets() <= 1)
		return false;

and likewise in the existing cpusets_enabled() check in 
get_page_from_freelist().  A root cpuset may not exclude mems on the 
system so, even if mounted, there's no need to check or be worried about 
concurrent change when there is only one cpuset.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/