Re: [RFC PATCH 0/4] mm/damon: Add DAMOS action to interleave data across nodes

[Bijan Tabatabai <bijan311@gmail.com>]

On Thu, Jun 12, 2025 at 9:42 PM Huang, Ying
<ying.huang@linux.alibaba.com> wrote:
>
> SeongJae Park <sj@kernel.org> writes:
>
> > Hi Bijan,
> >
> > On Thu, 12 Jun 2025 13:13:26 -0500 Bijan Tabatabai <bijan311@gmail.com> wrote:
> >
> >> From: Bijan Tabatabai <bijantabatab@micron.com>
> >>
> >> A recent patch set automatically set the interleave weight for each node
> >> according to the node's maximum bandwidth [1]. In another thread, the patch
> >> set's author, Joshua Hahn, wondered if/how these weights should be changed
> >> if the bandwidth utilization of the system changes [2].
> >
> > Thank you for sharing the background.  I do agree it is an important question.
> >
> >>
> >> This patch set adds the mechanism for dynamically changing how application
> >> data is interleaved across nodes while leaving the policy of what the
> >> interleave weights should be to userspace. It does this by adding a new
> >> DAMOS action: DAMOS_INTERLEAVE. We implement DAMOS_INTERLEAVE with both
> >> paddr and vaddr operations sets. Using the paddr version is useful for
> >> managing page placement globally. Using the vaddr version limits tracking
> >> to one process per kdamond instance, but the va based tracking better
> >> captures spacial locality.
> >>
> >> DAMOS_INTERLEAVE interleaves pages within a region across nodes using the
> >> interleave weights at /sys/kernel/mm/mempolicy/weighted_interleave/node<N>
> >> and the page placement algorithm in weighted_interleave_nid via
> >> policy_nodemask.
> >
> > So, what DAMOS_INTERLEAVE will do is, migrating pages of a given DAMON region
> > into multiple nodes, following interleaving weights, right?
Hi Ying,

> Hi, Bijan,
>
> It's hard for me to understand what you want to do in your original
> patch description.  SeongJae's description is helpful.  So, can you add
> more description in the future version?

Yes, sorry about that. I added more detail in my reply to SeongJae and
will include more detail in the cover letter of the next revision.

> So, you will migrate allocated pages to follow new weight?

Yes

> How to interact with the weight specified by users explicitly?  Usually we will
> respect explicit user policy.

I am not entirely sure I understand the question completely, but I
will try to answer
the best I can.

We interact with the user provided weights through the policy_nodemask function,
which gives us the node id a page should be on. This patch only reads the user
provided weights and migrates pages to be consistent with new weights provided
by the user, so I believe these changes do respect the explicit user
policy. Please let
me know if you disagree.

Thanks for the review,
Bijan

P.S. Sorry for sending this twice - I accidentally replied instead of
replied all.