Re: [RFC PATCH v5 00/10] mm: Hot page tracking and promotion infrastructure

[Gregory Price <gourry@gourry.net>]

On Mon, Feb 23, 2026 at 07:57:39PM +0530, Bharata B Rao wrote:
> 
> Time in seconds - Lower is better
> Mop/s total - Higher is better
> =====================================================================================
>                         Base            Base            pghot-default
> pghot-precise
>                         NUMAB0          NUMAB2          NUMAB2          NUMAB2
> =====================================================================================
> Time in seconds         7349.86         4422.50         6219.71         4113.56
> Mop/s total             53247.66        88493.630       62923.030       95139.810
> 
> pgpromote_success       0               42181834        248503390       41955718
> pgpromote_candidate     0               0               577086192       0
> pgpromote_candidate_nrl 0               42181834        29410329        41956171
> pgdemote_kswapd         0               0               216489010       0
> numa_pte_updates        0               42252749        607470975       42037882
> numa_hint_faults        0               42183772        606540729       41968150
> =====================================================================================
> 
> - In the base case, the benchmark numbers improve significantly due to hot page
>   promotion.
> - Though the benchmark runs for hundreds of minutes, the pages get promoted
>   within the first few mins.
> - pghot-precise is able to match the base case numbers.
> - The benchmark suffers in pghot-default case due to promotion being limited
>   to the default NID (0) only. This leads to excessive PTE updates, hint faults,
>   demotion and promotion churn.

Wow, this really seems to justify the extra memory usage.

Is it possible for you to change pghot-default to move the page to a
random (or round-robin) node on the top tier instead of NID(0) by default?

At least then pghot-default would be correct 1/N % of the time (in theory).
I'd be curious to see how close it gets to NUMAB2 with that.

~Gregory