From: Li Zhong <zhong@linux.vnet.ibm.com>
To: Cong Wang <xiyou.wangcong@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
akpm@linux-foundation.org
Subject: Re: [PATCH mm] limit the mm->map_count not greater than sysctl_max_map_count
Date: Wed, 18 Apr 2012 21:40:35 -0400 [thread overview]
Message-ID: <1334799635.10478.9.camel@ThinkPad-T420> (raw)
In-Reply-To: <4F8EC161.5050307@gmail.com>
On Wed, 2012-04-18 at 21:28 +0800, Cong Wang wrote:
> On 04/18/2012 05:27 PM, Li Zhong wrote:
> > When reading the mmap codes, I found the checking of mm->map_count
> > against sysctl_max_map_count is not consistent. At some places, ">" is
> > used; at some other places, ">=" is used.
> >
> > This patch changes ">" to">=", so they are consistent, and makes sure
> > the value is not greater (one more) than sysctl_max_map_count.
> >
>
> Well, according to Documentation/sysctl/vm.txt,
>
> max_map_count:
>
> This file contains the maximum number of memory map areas a process
> may have. [...]
>
> I think ->map_count == sysctl_max_map_count should be allowed, so using
> '>' is correct.
>
Yes, I agree that ->map_count == sysctl_max_map_count should be allowed.
However, with '>' used. The ->map_count could be sysctl_max_map_count+1.
It could be seen with a simple program doing continuously mmaping of a
file.
( Still it is possible, as stated in the comments of do_munmap code, if
the VMA is going to be divided into two, the map_count could temporarily
be sysctl_max_map_count+1, after the original vma split into two, and
before one of the two vmas removed. )
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WARNING: multiple messages have this Message-ID (diff)
From: Li Zhong <zhong@linux.vnet.ibm.com>
To: Cong Wang <xiyou.wangcong@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
akpm@linux-foundation.org
Subject: Re: [PATCH mm] limit the mm->map_count not greater than sysctl_max_map_count
Date: Wed, 18 Apr 2012 21:40:35 -0400 [thread overview]
Message-ID: <1334799635.10478.9.camel@ThinkPad-T420> (raw)
In-Reply-To: <4F8EC161.5050307@gmail.com>
On Wed, 2012-04-18 at 21:28 +0800, Cong Wang wrote:
> On 04/18/2012 05:27 PM, Li Zhong wrote:
> > When reading the mmap codes, I found the checking of mm->map_count
> > against sysctl_max_map_count is not consistent. At some places, ">" is
> > used; at some other places, ">=" is used.
> >
> > This patch changes ">" to">=", so they are consistent, and makes sure
> > the value is not greater (one more) than sysctl_max_map_count.
> >
>
> Well, according to Documentation/sysctl/vm.txt,
>
> max_map_count:
>
> This file contains the maximum number of memory map areas a process
> may have. [...]
>
> I think ->map_count == sysctl_max_map_count should be allowed, so using
> '>' is correct.
>
Yes, I agree that ->map_count == sysctl_max_map_count should be allowed.
However, with '>' used. The ->map_count could be sysctl_max_map_count+1.
It could be seen with a simple program doing continuously mmaping of a
file.
( Still it is possible, as stated in the comments of do_munmap code, if
the VMA is going to be divided into two, the map_count could temporarily
be sysctl_max_map_count+1, after the original vma split into two, and
before one of the two vmas removed. )
next prev parent reply other threads:[~2012-04-19 1:41 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-18 9:27 [PATCH mm] limit the mm->map_count not greater than sysctl_max_map_count Li Zhong
2012-04-18 9:27 ` Li Zhong
2012-04-18 13:28 ` Cong Wang
2012-04-18 13:28 ` Cong Wang
2012-04-19 1:40 ` Li Zhong [this message]
2012-04-19 1:40 ` Li Zhong
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