linux-kernel - Re: [PATCH] hugetlbfs: correct handling of negative input to /proc/sys/vm/nr

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Message-ID: <20110222100235.GA15652@csn.ul.ie>
Date:	Tue, 22 Feb 2011 10:02:36 +0000
From:	Mel Gorman <mel@....ul.ie>
To:	Petr Holasek <pholasek@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>, linux-mm@...ck.org
Subject: Re: [PATCH] hugetlbfs: correct handling of negative input to
	/proc/sys/vm/nr_hugepages

On Mon, Feb 21, 2011 at 04:47:49PM +0100, Petr Holasek wrote:
> When user insert negative value into /proc/sys/vm/nr_hugepages it will result
> in the setting a random number of HugePages in system (can be easily showed
> at /proc/meminfo output).

I bet you a shiny penny that the value of HugePages becomes the maximum
number that could be allocated by the system at the time rather than a
random value.

> This patch fixes the wrong behavior so that the
> negative input will result in nr_hugepages value unchanged.
> 

As pointed out elsewhere, nr_overcommit_hugepages also needs fixing but
the fix is essentially the same.

> Signed-off-by: Petr Holasek <pholasek@...hat.com>
> ---
>  mm/hugetlb.c |    3 +--
>  1 files changed, 1 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index bb0b7c1..f99d7a8 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1872,8 +1872,7 @@ static int hugetlb_sysctl_handler_common(bool obey_mempolicy,
>  	unsigned long tmp;
>  	int ret;
>  
> -	if (!write)
> -		tmp = h->max_huge_pages;
> +	tmp = h->max_huge_pages;
>  
>  	if (write && h->order >= MAX_ORDER)
>  		return -EINVAL;
> -- 
> 1.7.1
> 

-- 
Mel Gorman
SUSE Labs
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