Re: Memory tiering with DAMON/DAMOS auto-tuning

[SJ Park <sj@kernel.org>]

On Wed, 30 Sep 2026 19:26:31 +0300 Anton Gavriliuk <antosha20xx@gmail.com> wrote:

> I would go back to memory tiering VCF9.1-like behavior you helped me
> configure, for new few questions:
> 
> 1.  It works with the goal of 50% free memory for numa node 0, but
> when I tried to set 25% free memory, it didn't do anything...
> 
> [root@localhost ~]# COLUMNS=500 numastat -p $(pgrep valkey-server) | cat
> 
> Per-node process memory usage (in MBs) for PID 3808 (valkey-server)
>                            Node 0          Node 1          Node 2
>     Node 3           Total
>                   --------------- --------------- ---------------
> --------------- ---------------
> Huge                         0.00            0.00            0.00
>       0.00            0.00
> Heap                         0.11            0.00            0.00
>       0.00            0.11
> Stack                        0.03            0.00            0.00
>       0.00            0.03
> Private                 238356.25            2.19            3.42
>       0.00       238361.86
> ----------------  --------------- --------------- ---------------
> --------------- ---------------
> Total                   238356.39            2.19            3.42
>       0.00       238362.00
> [root@localhost ~]#

So, your workload is using ~232 GiB of node 0 memory and no demotion of it is
occurred.  According to your original mail [1], the node 0 has ~377 GiB memory.
If we make 25% of it free, it means it should have 75% of it (~282 GiB) be
utilized.  If the node0 has only your workload, it means node 0 memory
utilization is still only ~61%.  In other words, 25% free memory goal is
already achieved.  Than DAMON wouldn't do any demotion.

Does the theory makes sense?  Maybe you can confirm by checking the free memory
ratio of node 0.

[...]
> 2. If there are no un-accessed pages to demote for achieving a defined
> goal, damon will demote pages with the most rare access ?

No.  Because you set '--access_rate 0% 0%' for the demotion scheme, it will do
no demotion in the scenario.  You could try '--access_rate 0% max' if you want.
You may also need to remove '--damos_filter reject young' option from the
command if that is really what you want to do.

[1] https://lore.kernel.org/CAAiJnjp5F8ZuPG1gEsD_Wgs7Z+GToz67nzjr0490sz9y328=dg@mail.gmail.com


Thanks,
SJ

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