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

On Wed 13-10-21 18:40:26, Aneesh Kumar K.V wrote:

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

quoted

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

quoted

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.

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