Re: [PATCH v7 0/7] mm: Hot page tracking and promotion infrastructure

[Bharata B Rao]

On 11-May-26 8:08 PM, Gregory Price wrote:
> On Mon, May 11, 2026 at 04:07:16PM +0530, Bharata B Rao wrote:
>>
>> The entire point of this patchset is not just about improving the performance.
>> It is mainly about adding a new dedicated infrastructure for detecting and
>> promoting hot pages. It is about having a subsystem that can act as a single
>> source of truth page hotness in the kernel. Though we aren't there yet, we have
>> started by having a minimal infrastructure that centralizes the hot page
>> promotion and associated heuristics that currently sits in scheduler so that the
>> same can be used with other page hotness sources as well.
>>
> 
> The goal of hotness tracking in general is to improve performance.

Agreed. As I have mentioned elsewhere in the thread, right now we have just
moved the existing promotion mechanism to pghot, hence the initial concern has
been to ensure the earlier performance levels are still met with centralized
promotion engine that does batched promotions from non-process context.

> 
> The goal of PGHot should be a reasonable baseline for the kernel to
> course-correct LRU inversions across tiers over time, because LRU
> threads only scan invidiual nodes and don't compare across nodes.

Right.

> 
> I would hazard against trying to wholesale state it "Shall be the single
> source of truth", as we will inevitably discover some condition which is
> not covered / cannot be captured / we will simply get it wrong.

Yeah. The ideal goal of single source of truth may be a bit far fetched but
pghot is definitely a subsystem that can work with multiple page hotness
sources, aggregate hot signals from them and provide a single unified promotion
mechanism.

Regards,
Bharata.