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Old 03-15-2011, 02:48 PM
Pascal Vitoux
 
Default Bug#618485: linux-image-2.6.32-5-vserver-686: VM value in /proc/virtual/xxx/limit decreases abnormally

Package: linux-2.6
Version: 2.6.32-30
Severity: important

When a process starts and ends inside a virtual server, virtual memory reported
by /proc/virtual/xxx/limit (as VM) decreases (at least by 1). The value drifts
slowly and reaches negative values.

As long as no hard/soft limit is set, this bug seems to have no incidence.
Otherwise, the virtual server become unusable when virtual memory reaches
negative values (memory allocation failures, new process get killed)

Someone reports the same issue on linux-vserver mailling list :
http://list.linux-vserver.org/archive?mss:4894lhpkllgpffjhcfianop

After some tests and kernel rebuilds, it turns out that :
- previous version (2.6.32-29) is not affected
- drift does not occur when I exclude the patch debian/exec-Get-rid-of-
linux_binprm-vma_pages.patch

This patch is related to :
bugfix/all/exec-make-argv-envp-memory-visible-to-oom-killer.patch
bugfix/all/exec-copy-and-paste-the-fixes-into-compat_do_execve-paths.patch

-- Package-specific info:
** Version:
Linux version 2.6.32-5-vserver-686 (Debian 2.6.32-30) (ben@decadent.org.uk)
(gcc version 4.3.5 (Debian 4.3.5-4) ) #1 SMP Wed Jan 12 06:32:10 UTC 2011

** Command line:
BOOT_IMAGE=/boot/vmlinuz-2.6.32-5-vserver-686 root=UUID=bfc8ab24-de75-41cf-
8c2b-78686042fd9a ro quiet

-- System Information:
Debian Release: wheezy/sid
APT prefers testing
APT policy: (500, 'testing')
Architecture: i386 (i686)

-- vserver packages versions:
ii linux-image-2.6-vserver-686 2.6.32+29
Linux 2.6 for modern PCs (meta-package), Linux-VServer support
ii linux-image-2.6.32-5-vserver-686 2.6.32-30
Linux 2.6.32 for modern PCs, Linux-VServer support
ii linux-image-2.6.32-5-vserver-686-bigmem 2.6.32-30
Linux 2.6.32 for PCs with 4GB+ RAM, Linux-VServer support
ii linux-image-vserver-686 2.6.32+29
Linux for modern PCs (meta-package), Linux-VServer support
ii linux-image-vserver-686-bigmem 2.6.32+29
Linux for PCs with 4GB+ RAM (meta-package), Linux-VServer support
ii util-vserver 0.30.216-pre2864-2+b1
user-space tools for Linux-VServer virtual private servers
ii vserver-debiantools 0.8.0
Tools to manage debian virtual servers



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Archive: 20110315154843.4215.91351.reportbug@debian">http://lists.debian.org/20110315154843.4215.91351.reportbug@debian
 
Old 03-22-2011, 05:11 AM
Ben Hutchings
 
Default Bug#618485: linux-image-2.6.32-5-vserver-686: VM value in /proc/virtual/xxx/limit decreases abnormally

On Tue, 2011-03-15 at 16:48 +0100, Pascal Vitoux wrote:
> Package: linux-2.6
> Version: 2.6.32-30
> Severity: important
>
> When a process starts and ends inside a virtual server, virtual memory reported
> by /proc/virtual/xxx/limit (as VM) decreases (at least by 1). The value drifts
> slowly and reaches negative values.
>
> As long as no hard/soft limit is set, this bug seems to have no incidence.
> Otherwise, the virtual server become unusable when virtual memory reaches
> negative values (memory allocation failures, new process get killed)
>
> Someone reports the same issue on linux-vserver mailling list :
> http://list.linux-vserver.org/archive?mss:4894lhpkllgpffjhcfianop
>
> After some tests and kernel rebuilds, it turns out that :
> - previous version (2.6.32-29) is not affected
> - drift does not occur when I exclude the patch debian/exec-Get-rid-of-
> linux_binprm-vma_pages.patch

The purpose of this patch is to avoid an ABI change, which would be
disruptive to users who make use of external modules.

> This patch is related to :
> bugfix/all/exec-make-argv-envp-memory-visible-to-oom-killer.patch
> bugfix/all/exec-copy-and-paste-the-fixes-into-compat_do_execve-paths.patch
[...]

It looks like these don't do enough on VServer, anyway: the memory used
by arguments and environment is no longer hidden from the OOM killer, it
*is* hidden from VServer per-server accounting.

The attached patch (on top of 2.6.32-31) appears to fix this.

Ben.

--
Ben Hutchings
Once a job is fouled up, anything done to improve it makes it worse.
 

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