Re: [PATCH v6 0/1] mm/damon: add node_eligible_mem_bp and node_ineligible_mem_bp goal metrics

[Ravi Jonnalagadda <ravis.opensrc@gmail.com>]

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Hi SJ,

I will address your comments and the feedback from sashiko's review in the
next version of the patch.

Regarding the cover letter, I originally included it to provide context on
the general methodology. However, I agree that it is unnecessary for a
single patch. I will move the relevant content to the commit message and
drop the cover letter in the next iteration.

Thanks,
Ravi Jonnalagadda

On Sun, Apr 5, 2026 at 3:51 PM SeongJae Park <sj@kernel.org> wrote:

> Hello Ravi,
>
> On Sun,  5 Apr 2026 11:42:46 -0700 Ravi Jonnalagadda <
> ravis.opensrc@gmail.com> wrote:
>
> > Changes since v5:
> > =================
> >
> https://lore.kernel.org/linux-mm/20260404012215.1539-1-ravis.opensrc@gmail.com/
> >
> > - Rebased onto mm-new instead of damon/next for sashiko review
>
> Thank you for doing this.  sashiko was able to review and find some good
> points.  I shared the full review with my opinions as a reply to the patch
> 1.
> Please check and reply.
>
> > - Removed Reported-by/Closes tags per maintainer feedback (not needed
> >   for bugs found before merge)
> >
> > Changes since v4:
> > =================
> >
> https://lore.kernel.org/linux-mm/20260320190453.1430-1-ravis.opensrc@gmail.com/
> >
> > - Fixed commit message description for DAMOS_QUOTA_NODE_INELIGIBLE_MEM_BP
> >   per review feedback
> > - Added clarifying comment for ops-common.h include (for
> damon_get_folio())
> > - Fixed build error when CONFIG_DAMON_PADDR is disabled by adding
> >   #ifdef CONFIG_DAMON_PADDR guards around functions using
> damon_get_folio()
> > - Dropped RFC tag per maintainer feedback
> >
> > This patch is based on top of mm-new.
> >
> > Background and Motivation
> > =========================
> >
> > In heterogeneous memory systems, controlling memory distribution across
> > NUMA nodes is essential for performance optimization. This patch enables
> > system-wide page distribution with target-state goals such as "maintain
> > 30% of scheme-eligible memory on CXL" using PA-mode DAMON schemes.
> >
> > What These Metrics Measure
> > ==========================
> >
> > node_eligible_mem_bp:
> >     scheme_eligible_bytes_on_node / total_scheme_eligible_bytes * 10000
> >
> > node_ineligible_mem_bp:
> >     (total - scheme_eligible_bytes_on_node) / total * 10000
> >
> > These metrics are complementary: eligible_bp + ineligible_bp = 10000 bp.
>
> As I mentioned on sashiko review, I now think node_ineligible_mem_bp is a
> confusing name, and thinking a new name, maybe
> node_eligible_mem_bp_complement
> is better.  Let's further discuss on sashiko review reply thread.
>
> >
> > Two-Scheme Setup for Hot Page Distribution
> > ==========================================
> >
> > For maintaining hot memory on DRAM (node 0) and CXL (node 1) in a 7:3
> > ratio:
> >
> >     PUSH scheme: migrate_hot from node 0 -> node 1
> >       goal: node_ineligible_mem_bp, nid=0, target=3000
> >       "Move hot pages from DRAM to CXL if more than 70% of hot data is
> >        in DRAM"
> >
> >     PULL scheme: migrate_hot from node 1 -> node 0
> >       goal: node_eligible_mem_bp, nid=0, target=7000
> >       "Move hot pages from CXL to DRAM if less than 70% of hot data is
> >        in DRAM"
> >
> > The complementary goals create a feedback loop that converges to the
> > target distribution.
> >
> > Testing Results
> > ===============
> >
> > Functionally tested on a two-node heterogeneous memory system with DRAM
> > (node 0) and CXL memory (node 1). A PUSH+PULL scheme configuration using
> > migrate_hot actions was used to reach a target hot memory ratio between
> > the two tiers. Testing used the TEMPORAL goal tuner available in
> > damon/next and mm-unstable.
> >
> > With the TEMPORAL tuner, the system converges quickly to the target
> > distribution. The tuner drives esz to maximum when under goal and to
> > zero once the goal is met, forming a simple on/off feedback loop that
> > stabilizes at the desired ratio.
> >
> > With the CONSIST tuner, the scheme still converges but more slowly, as
> > it migrates and then throttles itself based on quota feedback. The time
> > to reach the goal varies depending on workload intensity.
> >
> > Note: These metrics work with both TEMPORAL and CONSIST goal tuners.
> >
> > Ravi Jonnalagadda (1):
> >   mm/damon: add node_eligible_mem_bp and node_ineligible_mem_bp goal
> >     metrics
> >
> >  include/linux/damon.h    |   6 ++
> >  mm/damon/core.c          | 188 ++++++++++++++++++++++++++++++++++++---
> >  mm/damon/sysfs-schemes.c |  12 +++
> >  3 files changed, 192 insertions(+), 14 deletions(-)
>
> Btw, having a cover letter for single patch looks odd.  Why don't you add
> this
> cover letter to the patch's commit message?
>
>
> Thanks,
> SJ
>
> [...]
>

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