lkml.org 
[lkml]   [2022]   [Mar]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] mm: migrate: set demotion targets differently
Date
Baolin Wang <baolin.wang@linux.alibaba.com> writes:

> On 3/29/2022 10:04 PM, Jagdish Gediya wrote:
>> On Tue, Mar 29, 2022 at 08:26:05PM +0800, Baolin Wang wrote:
>> Hi Baolin,
>>> Hi Jagdish,
>>>
>>> On 3/29/2022 7:52 PM, Jagdish Gediya wrote:
>>>> The current implementation to identify the demotion
>>>> targets limits some of the opportunities to share
>>>> the demotion targets between multiple source nodes.
>>>>
>>>> Implement a logic to identify the loop in the demotion
>>>> targets such that all the possibilities of demotion can
>>>> be utilized. Don't share the used targets between all
>>>> the nodes, instead create the used targets from scratch
>>>> for each individual node based on for what all node this
>>>> node is a demotion target. This helps to share the demotion
>>>> targets without missing any possible way of demotion.
>>>>
>>>> e.g. with below NUMA topology, where node 0 & 1 are
>>>> cpu + dram nodes, node 2 & 3 are equally slower memory
>>>> only nodes, and node 4 is slowest memory only node,
>>>>
>>>> available: 5 nodes (0-4)
>>>> node 0 cpus: 0 1
>>>> node 0 size: n MB
>>>> node 0 free: n MB
>>>> node 1 cpus: 2 3
>>>> node 1 size: n MB
>>>> node 1 free: n MB
>>>> node 2 cpus:
>>>> node 2 size: n MB
>>>> node 2 free: n MB
>>>> node 3 cpus:
>>>> node 3 size: n MB
>>>> node 3 free: n MB
>>>> node 4 cpus:
>>>> node 4 size: n MB
>>>> node 4 free: n MB
>>>> node distances:
>>>> node 0 1 2 3 4
>>>> 0: 10 20 40 40 80
>>>> 1: 20 10 40 40 80
>>>> 2: 40 40 10 40 80
>>>> 3: 40 40 40 10 80
>>>> 4: 80 80 80 80 10
>>>>
>>>> The existing implementation gives below demotion targets,
>>>>
>>>> node demotion_target
>>>> 0 3, 2
>>>> 1 4
>>>> 2 X
>>>> 3 X
>>>> 4 X
>>>>
>>>> With this patch applied, below are the demotion targets,
>>>>
>>>> node demotion_target
>>>> 0 3, 2
>>>> 1 3, 2
>>>> 2 3
>>>> 3 4
>>>> 4 X
>>>
>>> Node 2 and node 3 both are slow memory and have same distance, why node 2
>>> should demote cold memory to node 3? They should have the same target
>>> demotion node 4, which is the slowest memory node, right?
>>>
>> Current demotion target finding algorithm works based on best distance, as distance between node 2 & 3 is 40 and distance between node 2 & 4 is 80, node 2 demotes to node 3.
>
> If node 2 can demote to node 3, which means node 3's memory is colder
> than node 2, right? The accessing time of node 3 should be larger than
> node 2, then we can demote colder memory to node 3 from node 2.
>
> But node 2 and node 3 are same memory type and have same distance, the
> accessing time of node 2 and node 3 should be same too, so why add so
> many page migration between node 2 and node 3? I'm still not sure the
> benefits.
>
> Huang Ying and Dave, how do you think about this demotion targets?

Yes. I think the demotion target of 2 should be 4, as in my another
email in this thread. Demoting from 2 to 3 makes no sense.

Best Regards,
Huang, Ying

[snip]

\
 
 \ /
  Last update: 2022-03-30 08:55    [W:0.519 / U:0.068 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site