[Devel] Re: [PATCH v5 3/3] cgroups: make procs file writable

[David Rientjes]

On Mon, 27 Dec 2010, Ben Blum wrote:

> > I'm not sure what the benefit of defining it as a macro would be.  You're 
> > defining these statically allocated nodemasks so they have file scope, I 
> > hope (so they can be shared amongst the users who synchronize on 
> > cgroup_lock() already).
> 
> In the attach() case, yes, but in other cases I was thinking they could
> be put on the stack if CONFIG_NODES_SHIFT < 8, and static but still
> per-function otherwise. Or should all the functions share the same
> global nodemask?
> 

I think it would be appropriate to use a shared nodemask with file scope 
whenever you have cgroup_lock() to avoid the unnecessary kmalloc() even 
with GFP_KERNEL.  Cpusets are traditionally used on very large machines in 
the first place, so there is a higher likelihood that 
CONFIG_NODES_SHIFT > 8 whenever CONFIG_CPUSETS is enabled.

All users of NODEMASK_ALLOC() should be protected by cgroup_lock() other 
than cpuset_sprintf_memlist(), right?  That should be the only remaining 
user of NODEMASK_ALLOC() and works well since it can return -ENOMEM.
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