Re: [PATCH] IPC initialize shmmax and shmall from the current value not the default

[Manfred Spraul]

Hi Marian,

Note: The limits will soon be increased to (nearly) ULONG_MAX.
I.e.: If you propose the patch because you are running into issues with 
a too small SEMMAX after an unshare(CLONE_NEWIPC), then this will be 
fixed soon.


On 05/04/2014 01:53 AM, Davidlohr Bueso wrote:
> On Sun, 2014-05-04 at 01:48 +0300, Marian Marinov wrote:
> > When we are creating new IPC namespace that should be cloned from the current namespace it is a good idea to copy the
> > values of the current shmmax and shmall to the new namespace.
The idea sounds reasonable:
If an admin has reduced the limits, then the reduction should also apply 
after a unshare(CLONE_NEWIPC).

But:
Your patch doesn't use the current shmmax, it uses the shmmax from 
init_ipc_ns.
Would it be possible to use the current values?

> Why is this a good idea?
>
> This would break userspace that relies on the current behavior.
> Furthermore we've recently changed the default value of both these
> limits to be as large as you can get, thus deprecating them. I don't
> like the idea of this being replaced by namespaces.
Davidlohr: We are not deprecating them, we make the default huge.
The limits should stay as usable as they were.

With regards to breaking user space, I must think about it a bit more.
Right now, each new namespace starts with SEMMAX=32MB, i.e. an often 
unusable default.

--
    Manfred
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