/proc/<pid>/maps question....why aren't adjacent memory chunks merged?

/proc/<pid>/maps question....why aren't adjacent memory chunks merged?

[Chris Friesen]

Hi,

I've got a system running a somewhat-modified 2.6.27 on 64-bit x86.

While investigating a userspace memory leak issue I noticed that
/proc/<pid>/maps showed a bunch of adjacent anonymous memory chunks with
identical permissions:

7fd048000000-7fd04c000000 rw-p 00000000 00:00 0
7fd04c000000-7fd050000000 rw-p 00000000 00:00 0
7fd050000000-7fd054000000 rw-p 00000000 00:00 0
7fd054000000-7fd058000000 rw-p 00000000 00:00 0
7fd058000000-7fd05c000000 rw-p 00000000 00:00 0
7fd05c000000-7fd060000000 rw-p 00000000 00:00 0
7fd060000000-7fd064000000 rw-p 00000000 00:00 0
7fd064000000-7fd068000000 rw-p 00000000 00:00 0
7fd068000000-7fd06c000000 rw-p 00000000 00:00 0
7fd06c000000-7fd070000000 rw-p 00000000 00:00 0
7fd070000000-7fd074000000 rw-p 00000000 00:00 0
7fd074000000-7fd078000000 rw-p 00000000 00:00 0
7fd078000000-7fd07c000000 rw-p 00000000 00:00 0
7fd07c000000-7fd07fffe000 rw-p 00000000 00:00 0

I was under the impression that the kernel would merge areas together in
this circumstance.  Does anyone have an idea about what's going on here?

Thanks,

Chris

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Re: /proc/<pid>/maps question....why aren't adjacent memory chunks merged?

[Américo Wang]

On Thu, May 13, 2010 at 03:34:04PM -0600, Chris Friesen wrote:
>Hi,
>
>I've got a system running a somewhat-modified 2.6.27 on 64-bit x86.
>
>While investigating a userspace memory leak issue I noticed that
>/proc/<pid>/maps showed a bunch of adjacent anonymous memory chunks with
>identical permissions:
>
>7fd048000000-7fd04c000000 rw-p 00000000 00:00 0
>7fd04c000000-7fd050000000 rw-p 00000000 00:00 0
>7fd050000000-7fd054000000 rw-p 00000000 00:00 0
>7fd054000000-7fd058000000 rw-p 00000000 00:00 0
>7fd058000000-7fd05c000000 rw-p 00000000 00:00 0
>7fd05c000000-7fd060000000 rw-p 00000000 00:00 0
>7fd060000000-7fd064000000 rw-p 00000000 00:00 0
>7fd064000000-7fd068000000 rw-p 00000000 00:00 0
>7fd068000000-7fd06c000000 rw-p 00000000 00:00 0
>7fd06c000000-7fd070000000 rw-p 00000000 00:00 0
>7fd070000000-7fd074000000 rw-p 00000000 00:00 0
>7fd074000000-7fd078000000 rw-p 00000000 00:00 0
>7fd078000000-7fd07c000000 rw-p 00000000 00:00 0
>7fd07c000000-7fd07fffe000 rw-p 00000000 00:00 0
>
>I was under the impression that the kernel would merge areas together in
>this circumstance.  Does anyone have an idea about what's going on here?
>

Well, that is not so simple, there are other considerations,
you need to check vma_merge(), especially can_vma_merge_{after,before}().

Thanks.

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