Re: [RFC PATCH v0 0/2] Batch migration for NUMA balancing

[Gregory Price <gourry@gourry.net>]

On Wed, May 21, 2025 at 11:45:52AM -0700, SeongJae Park wrote:
> Hi Bharata,
> 
> On Wed, 21 May 2025 13:32:36 +0530 Bharata B Rao <bharata@amd.com> wrote:
> 
> > Hi,
> > 
> > This is an attempt to convert the NUMA balancing to do batched
> > migration instead of migrating one folio at a time. The basic
> > idea is to collect (from hint fault handler) the folios to be
> > migrated in a list and batch-migrate them from task_work context.
> > More details about the specifics are present in patch 2/2.
> > 
> > During LSFMM[1] and subsequent discussions in MM alignment calls[2],
> > it was suggested that separate migration threads to handle migration
> > or promotion request may be desirable. Existing NUMA balancing, hot
> > page promotion and other future promotion techniques could off-load
> > migration part to these threads. Or if we manage to have a single
> > source of hotness truth like kpromoted[3], then that too can hand
> > over migration requests to the migration threads. I am envisaging
> > that different hotness sources like kmmscand[4], MGLRU[5], IBS[6]
> > and CXL HMU would push hot page info to kpromoted, which would
> > then isolate and push the folios to be promoted to the migrator
> > thread.
> 
> I think (or, hope) it would also be not very worthless or rude to mention other
> existing and ongoing works that have potentials to serve for similar purpose or
> collaborate in future, here.
> 
> DAMON is designed for a sort of multi-source access information handling.  In
> LSFMM, I proposed[1] damon_report_access() interface for making it easier to be
> extended for more types of access information.  Currenlty damon_report_access()
> is under early development.  I think this has a potential to serve something
> similar to your single source goal.
> 

It seems to me that DAMON might make use of the batch migration
interface, so if you need any changes or extensions, it might be good
for you (SJ) to take a look at that for us.

~Gregory