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

[Bharata B Rao]

On 23-Feb-26 8:32 PM, Gregory Price wrote:
> 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.

For pghot-default, with target_nid alternating between the available
toptier nodes 0 and 1, the numbers catch up with pghot-precise and base
NUMAB2 case as seen below:
================================
Time in seconds         4337.98
Mop/s total             90217.86

pgpromote_success       42170085
pgpromote_candidate     0
pgpromote_candidate_nrl 42171963
pgdemote_kswapd         0
numa_pte_updates        42338538
numa_hint_faults        42185662
================================

Regards,
Bharata.