Re: [PATCH 3/3] ipc namespace: copy settings from parent namespace

From: Manfred Spraul
Date: Tue Aug 12 2014 - 16:39:16 EST

Hi Eric,

On 08/12/2014 12:37 PM, Eric W. Biederman wrote:
Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> writes:

Sigh. Patches for new code during the merge window. It is a really
rotten time to look at new things.

Right now, each new IPC namespace starts with the kernel default values.
This means that changes that were made to the limits get overwritten.

With this patch, a new namespace inherits the settings from the parent
namespace, which is less surprising.
In principle I agree.

In practice I have to ask what have you done to survey applications
that use the ipc namespace to see if they will break with this change in
I know this is the wrong answer, but:
What I find are problems caused by the current behavior.

See e.g.:

Some background:
The e.g. sysvshm limits were not updated for many years and many
applications only ran properly if sysvshm limits are increased.
(now the defaults are large, but only since ~3.15)

Increasing is simple: sysctl kernel.shmmax=<>, but somehow this
must happen inside the container.

Right now, the most common approach seems to be the solution from the bugzilla above:
Just marc /proc as read-write and do it manually.

With the patch, the kernel would propagate the value from parent to child.

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