Re: Roadmap for extending DAMON beyond pte-accessed bit

[SJ Park <sj@kernel.org>]

On Fri, 10 Jul 2026 17:48:08 -0700 SJ Park <sj@kernel.org> wrote:

> On Wed, 24 Jun 2026 07:56:14 -0700 SeongJae Park <sj@kernel.org> wrote:
> 
> > On Mon, 25 May 2026 15:52:08 -0700 SeongJae Park <sj@kernel.org> wrote:
> > 
> > > Hello,
> > > 
> > > 
> > > TLDR: Let's extend DAMON for data attributes monitoring, andd then further
> > > extend that for multiple access check primitives including page faults, perf
> > > memory-access events and optimized AMD IBS-like h/w feature drivers.
> > [...] 
> > > Roadmap
> > > =======
> > > 
> > > Assuming you agree to use the data attributes monitoring interface, I suggest
> > > us to do the work in below roadmap.
> > > 
> > > Milestone 1: PTE Accessed bit as one of the data attributes
> > > -----------------------------------------------------------
> > > 
> > > I will work on stabilizing and further extending the data attributes interface
> > > and internal framework to be able to support PTE Accessed bit.  This may take
> > > no small amount of efforts, but hopefully doable by the end of this year.
> > 
> > Let me share more detailed plan for this milestone.  Nothing is set on the
> > stone.  Everything can be changed on the road.
> > 
> > The overall goal is, making attributes monitoring be able to do everything we
> > are doing now with PTE Accessed-bit based monitoring.  It is needed because we
> > want to do everythin we can do now with the PMU/page fault-based DAMON.  Also
> > it is needed because we will need to deprecate nr_accesses in long term without
> > breaking users.  For this, below changes will be made.
[...]
> > 3. Extend attrs for PTE Accessed bit check
> > 
> > Further, we will extend DAMON attributes monitoring to handle PTE Accessed bit
> > check.  We will extend it to let users configure probing preparation
> > operations.  The first operation to support will be the PTE Accessed bit
> > clearing operation.  Together, we will introduce new DAMON probe filter that
> > checks the PTE Accessed bit.  Using those, users will be able to do the
> > PTE Accessed bit based access monitoring in attrs-only monitoring mode.
> 
> I have a hacking level prototype for this in damon/next tree.  I will take more
> time for stabilizing it.  I'm aiming to make this be merged into 7.4-rc1.

The patch series [1] for this is now merged into mm.git.  Hopefully it will be
merged into 7.4-rc1 as planned.

Note that the series is supporting only paddr.  I'm working on extending it for
vaddr.  Actually there were user requests for this.  A working prototype is in
damon/next.

> 
> > 
> > 4. Extend attrs for DAMOS
> > 
> > Finally, we will extend DAMOS to be able to run with probe_hits.  That is, it
> > will be extended to let users configure the DAMOS target access pattern and do
> > its quota-prioritization based on the probe_hits.
> > 
> > After the four major changes are made, the attributes only mode DAMON can do
> > everything current DAAMON is doing, without nr_accesses.  We will then move on
> > to the milestone 2 of this project, and start a long term nr_accesses
> > deprecation.
> > 
> > I hope all changes to be landed by 7.5-rc1.

I'm now working on this.  Actually there were user requests for this.  A
working prototype implementation of an essential change is in damon/next.
Hopefully that will be landed by 7.5-rc1.  Some additional works for full DAMOS
support are expected, and those may be done after 7.5-rc1.

> 
> So I believe we are still on the track :)
> 
> [1] moving sum: https://lore.kernel.org/20260703170605.94472-1-sj@kernel.org
> [2] attrs-only: https://lore.kerrnel.org/20260710134651.18084-1-sj@kernel.org
> [3] attrs-only enqueue notice:
>     https://lore.kernel.org/20260710202349.2F2DA1F000E9@smtp.kernel.org/

[1] https://lore.kernel.org/20260901132506.99243-1-sj@kernel.org


Thanks,
SJ

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