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

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On Wed 13-10-21 18:40:26, Aneesh Kumar K.V wrote:
> On 10/13/21 18:37, Michal Hocko wrote:
> > On Wed 13-10-21 18:28:40, Aneesh Kumar K.V wrote:
> > > On 10/13/21 18:20, Michal Hocko wrote:
> > [...]
> > > > I am still not sure the semantic makes sense though. Why should
> > > > the lowest node in the nodemask have any special meaning? What if it is
> > > > a node with a higher number that somebody preferes to start with?
> > > > 
> > > 
> > > That is true. I haven't been able to find an easy way to specify the
> > > preferred node other than expressing it as first node in the node mask. Yes,
> > > it limits the usage of the policy. Any alternate suggestion?
> > 
> > set_mempolicy is indeed not very suitable for something you are looking
> > for. Could you be more specific why the initial node is so important?
> > Is this because you want to allocate from a cpu less node first before
> > falling back to others?
> > 
> 
> One of the reason is that the thread that is faulting in pages first is not
> the one that is going to operate on this page long term. Application wants
> to hint the allocation node for the same reason they use MPOL_PREFERRED now.

Why cannot you move the faulting thread to a numa node of the preference
during the faulting and them move it out if that is really necessary?
-- 
Michal Hocko
SUSE Labs




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