Re: [RFC PATCH] mm/mempolicy: add MPOL_PREFERRED_STRICT memory policy

["Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>]

Michal Hocko <mhocko@suse.com> writes:

> On Wed 13-10-21 18:53:55, Aneesh Kumar K.V wrote:
>> On 10/13/21 18:46, Andi Kleen wrote:
>> > 
>> > > The difference with MPOL_BIND is the ability to specify a preferred node
>> > > which is the first node in the nodemask argument passed.
>> > 
>> > That's always the one with the lowest number. Isn't that quite limiting
>> > in practice?
>> > 
>> > It seems if you really want to do that you would need another argument.
>> > 
>> Yes. But that would make it a new syscall. Should we do that?
>
> Yes, I do not see any reasonable to cram this into the existing syscall.
> I am not yet sure what the syscall should look like though. I can see
> two usecases, one of the is a very specific node allocation fallback
> order requirement and another one is preferrence for a cpu less node
> over other nodes. Both are slightly different.

How about

SYSCALL_DEFINE5(preferred_mbind, unsigned long, start, unsigned long, len,
		unsigned long, preferred_node, const unsigned long __user *, nmask,
		unsigned long, maxnode)
{
	return kernel_mbind(start, len, MPOL_PREFERRED_STRICT, preferred_node,
			    nmask, maxnode, 0);
}