linux-kernel - Re: [PATCH v2 1/5] mm: demotion: Set demotion list differently

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Message-ID: <4288cbad49690d7c4eb2b1d705eea01221ab8328.camel@intel.com>
Date:   Thu, 14 Apr 2022 15:09:42 +0800
From:   "ying.huang@...el.com" <ying.huang@...el.com>
To:     Jagdish Gediya <jvgediya@...ux.ibm.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     akpm@...ux-foundation.org, aneesh.kumar@...ux.ibm.com,
        baolin.wang@...ux.alibaba.com, dave.hansen@...ux.intel.com
Subject: Re: [PATCH v2 1/5] mm: demotion: Set demotion list differently

On Wed, 2022-04-13 at 14:52 +0530, Jagdish Gediya wrote:
> Sharing used_targets between multiple nodes in a single
> pass limits some of the opportunities for demotion target
> sharing.
> 
> Don't share the used targets between multiple nodes in a
> single pass, instead accumulate all the used targets in
> source nodes shared by all pass, and reset 'used_targets'
> to source nodes while finding demotion targets for any new
> node.
> 
> This results into some more opportunities to share demotion
> targets between multiple source nodes, 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              4
>  3              4
>  4              X
> 
> e.g. with below NUMA topology, where node 0, 1 & 2 are
> cpu + dram nodes and node 3 is slow memory node,
> 
> available: 4 nodes (0-3)
> 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: 4 5
> node 2 size: n MB
> node 2 free: n MB
> node 3 cpus:
> node 3 size: n MB
> node 3 free: n MB
> node distances:
> node   0   1   2   3
>   0:  10  20  20  40
>   1:  20  10  20  40
>   2:  20  20  10  40
>   3:  40  40  40  10
> 
> The existing implementation gives below demotion targets,
> 
> node    demotion_target
>  0              3
>  1              X
>  2              X
>  3              X
> 
> With this patch applied, below are the demotion targets,
> 
> node    demotion_target
>  0              3
>  1              3
>  2              3
>  3              X
> 

With the [PATCH v1], you have describe the demotion order changes for
the following system, I guess there's no change with [PATCH v2]?

With below NUMA topology, where node 0 & 2 are cpu + dram
nodes and node 1 & 3 are slow memory nodes,

available: 4 nodes (0-3)
node 0 cpus: 0 1
node 0 size: n MB
node 0 free: n MB
node 1 cpus:
node 1 size: n MB
node 1 free: n MB
node 2 cpus: 2 3
node 2 size: n MB
node 2 free: n MB
node 3 cpus:
node 3 size: n MB
node 3 free: n MB
node distances:
node   0   1   2   3
  0:  10  40  20  80
  1:  40  10  80  80
  2:  20  80  10  40
  3:  80  80  40  10

And, what is the demotion order for the following system with [PATCH
v2]?

Node 0 & 2 are cpu + dram nodes and node 1 are slow
memory node near node 0,

available: 3 nodes (0-2)
node 0 cpus: 0 1
node 0 size: n MB
node 0 free: n MB
node 1 cpus:
node 1 size: n MB
node 1 free: n MB
node 2 cpus: 2 3
node 2 size: n MB
node 2 free: n MB
node distances:
node   0   1   2
  0:  10  40  20
  1:  40  10  80
  2:  20  80  10

Best Regards,
Huang, Ying


[snip]