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

On 10/13/21 18:37, Michal Hocko wrote:

On Wed 13-10-21 18:28:40, Aneesh Kumar K.V wrote:

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On 10/13/21 18:20, Michal Hocko wrote:

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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.

-aneesh