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

[Baolin Wang]

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];