Re: [RFC PATCH] mm: migrate: Add new node demotion strategy

[Baolin Wang]

On 2021/11/8 16:12, Huang, Ying writes:
> Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> writes:
>
> > On 2021/11/8 14:48, Huang, Ying writes:
> > > Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx> writes:
> > >
> > > > On 2021/11/7 23:20, Dave Hansen wrote:
> > > > > On 11/7/21 1:33 AM, Baolin Wang wrote:
> > > > > > Thanks for your suggestion. After some thinking, can we change the
> > > > > > node_demotion[] structure like below? Which means one source node can be
> > > > > > demoted to mutiple target node, and we can set up the target node mask
> > > > > > according to the node distance. How do you think? Thanks.
> > > > > >
> > > > > > static nodemask_t node_demotion[MAX_NUMNODES] __read_mostly =
> > > > > >        {[0 ... MAX_NUMNODES - 1] = NODE_MASK_NONE};
> > > > > How large is that in the worst case?
> > > >
> > > > For the worst case (MAX_NUMNODES=1024), the size of the node_demotion
> > > > is 131072 bytes, while the size of original data structure is 4096
> > > > bytes. Maybe we can allocate the node_demotion dynamically?
> > > Per my understanding, in most cases, the number of demotion target
> > > nodes
> > > should be quite small.  So why not restrict the number of demotion
> > > target nodes to make it some kind of simple array?
> >
> > Yes, agree. Something like below is reasonable for you?
> >
> > #define DEMOTION_TARGET_NODES 16
> > typedef struct { DECLARE_BITMAP(bits, DEMOTION_TARGET_NODES); }
> > demotemask_t;
> >
> > static demotemask_t node_demotion[MAX_NUMNODES];
>
> I don't think we need a bitmap.  May be something as following,
>
> #define DEMOTION_TARGET_NODES 15
> struct demotion_nodes {
>    unsigned short nr;
>    unsigned short nodes[DEMOTION_TARGET_NODES];
> };

OK. Let me try it in next version. Thanks.