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

From: Baolin Wang
Date: Mon Nov 08 2021 - 02:06:37 EST




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];