Re: [PATCH v31 02/13] mm/damon/core: Implement region-based sampling

[Shakeel Butt]

On Mon, Jun 21, 2021 at 1:31 AM SeongJae Park <sj38.park@xxxxxxxxx> wrote:
>
> From: SeongJae Park <sjpark@xxxxxxxxx>
>
> To avoid the unbounded increase of the overhead, DAMON groups adjacent
> pages that are assumed to have the same access frequencies into a
> region.  As long as the assumption (pages in a region have the same
> access frequencies) is kept, only one page in the region is required to
> be checked.  Thus, for each ``sampling interval``,
>
>  1. the 'prepare_access_checks' primitive picks one page in each region,
>  2. waits for one ``sampling interval``,
>  3. checks whether the page is accessed meanwhile, and
>  4. increases the access count of the region if so.
>
> Therefore, the monitoring overhead is controllable by adjusting the
> number of regions.  DAMON allows both the underlying primitives and user
> callbacks to adjust regions for the trade-off.  In other words, this
> commit makes DAMON to use not only time-based sampling but also
> space-based sampling.
>
> This scheme, however, cannot preserve the quality of the output if the
> assumption is not guaranteed.  Next commit will address this problem.
>
> Signed-off-by: SeongJae Park <sjpark@xxxxxxxxx>
> Reviewed-by: Leonard Foerster <foersleo@xxxxxxxxx>
> Reviewed-by: Fernand Sieber <sieberf@xxxxxxxxxx>

Acked-by: Shakeel Butt <shakeelb@xxxxxxxxxx>