Re: [RFC PATCH] mm/damon: fix damos quota walk-position tracking

[SJ Park <sj@kernel.org>]

On Tue, 25 Aug 2026 20:46:16 +0800 Liew Rui Yan <aethernet65535@gmail.com> wrote:

> DAMOS uses charge_target_from/charge_addr_from to remember how far a
> quota-limited walk has progressed.  The current implementation has two
> problems:
> 
> 1. Once set, the cursor unconditionally skips and resets at the last
>    region of the tracked target, so the last region can be skipped even
>    when it has not been processed.

I don't fully understand this.  Could you please clarify more?  Maybe adding a
realistic example scenario would be helpful.

> 
> 2. The cursor only advances when the quota becomes full.  Regions that
>    are filtered out do not move the cursor, and the scheme can remain
>    stuck on the same regions.

I don't fully understand this, either.  Could you pleae clarify more?

> 
> Fix this by treating the fields as a rotating walk cursor:
> 
> - Advance the cursor for every region walked while a quota is set,
>   regardless of whether the region is applied or filtered out.
> - Remove the unconditional last-region reset.
> - Skip regions before the cursor, and rotate to the next valid target
>   only after the current target has been fully walked.
> - Rename charge_{target,addr}_from to walk_{target,addr}_from and
>   damos_skip_charged_region() to damos_skip_walked_region().

Because I don't understand the problem, I can't understand benefit of this
change.  Again, more clarification would be helpful.

> 
> Signed-off-by: Liew Rui Yan <aethernet65535@gmail.com>
> ---
>  include/linux/damon.h |   6 +-
>  mm/damon/core.c       | 156 +++++++++++++++++++++++++++++-------------
>  2 files changed, 111 insertions(+), 51 deletions(-)

Quite amount of change.  I will review the code after the high level
understanding is done.


Thanks,
SJ

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