Re: [RFC PATCH 0/4] mm/damon: add DAMOS_MIGRATE_{HOT,COLD} destination nodes and weights

[SeongJae Park <sj@kernel.org>]

On Tue,  1 Jul 2025 17:39:37 -0500 Bijan Tabatabai <bijan311@gmail.com> wrote:

> On Sat, 21 Jun 2025 10:31:27 -0700 SeongJae Park <sj@kernel.org> wrote:
> 
> > DAMOS_MIGRATE_{HOT,COLD} action can migrate pages to only single node.
> > It could be useful to allow it migrates pages to multiple nodes with
> > different weights.  A work for dynamic interleaving[1] is in progress.
> > We also discussed this could be useful for memory tiering, e.g., when we
> > want to move pages to multiple noes of same tier.
> > 
> > Extend the API and ABI interface for specifying the multiple destination
> > nodes and their weights.
> > 
> > Note that this RFC is a prototype of the interface change for Bijan's
> > interleaving work[1].  Hence this patch series is only implementing the
> > interface part, not the real implementation of the migration behavior.
> > 
> > [1] https://lore.kernel.org/20250620180458.5041-1-bijan311@gmail.com
> > [2] https://lore.kernel.org/20240408175228.91414-1-sj@kernel.org
> > 
> > SeongJae Park (4):
> >   mm/damon: add struct damos_migrate_dest
> >   mm/damon/core: add damos->migrate_dest field
> >   mm/damon/sysfs-schemes: implement DAMOS action destinations directory
> >   mm/damon/sysfs-schemes: set damos->migrate_dest
> > 
> >  include/linux/damon.h    |  29 ++++-
> >  mm/damon/core.c          |   4 +
> >  mm/damon/sysfs-schemes.c | 253 ++++++++++++++++++++++++++++++++++++++-
> >  3 files changed, 282 insertions(+), 4 deletions(-)
> > 
> > 
> > base-commit: 78745efafbb93197e476717385616ed57ea2df22
> > -- 
> > 2.39.5
> 
> Hi SeongJae,
> 
> Thanks for putting this patch together. Sorry for taking a while to
> respond to it.

No worry!

> 
> I am finishing up V3 of the interleave patchset using these patches. It
> has mostly worked great, but I noticed that damos->migrate_dest was not
> being updated in damos_commit(), so new weights would not be applied. This
> meant that you could not update the interleave weights by committing the
> damon state. I also saw that damos->target_nid was also not being updated
> here. I will will have a patch fixing

Nice catch, thank you for finding the bug and making the fix!

> this with the V3 of the interleave
> patchset that I will hopefully send out tomorrow.

I cannot wait, but please take your time! :)


Thanks,
SJ

[...]