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Docs/mm/damon/design: document allow/reject DAMOS filter behaviors

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Update DAMOS filters design document to describe the allow/reject behavior
of filters.

Link: https://lkml.kernel.org/r/20250109175126.57878-8-sj@kernel.org
Signed-off-by: SeongJae Park <sj@kernel.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
SeongJae Park 2025-01-09 09:51:23 -08:00 • committed by Andrew Morton
parent faa636c0ec
commit f477b9b409
1 changed files with 29 additions and 4 deletions
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33
Documentation/mm/damon/design.rst
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@ -504,9 +504,34 @@ have a list of latency-critical processes.
To let users optimize DAMOS schemes with such special knowledge, DAMOS provides
a feature called DAMOS filters. The feature allows users to set an arbitrary
number of filters for each scheme. Each filter specifies the type of target
memory, and whether it should exclude the memory of the type (filter-out), or
all except the memory of the type (filter-in).
number of filters for each scheme. Each filter specifies
- a type of memory (``type``),
- whether it is for the memory of the type or all except the type
(``matching``), and
- whether it is to allow (include) or reject (exclude) applying
the scheme's action to the memory (``allow``).
When multiple filters are installed, each filter is evaluated in the installed
order. If a part of memory is matched to one of the filter, next filters are
ignored. If the memory passes through the filters evaluation stage because it
is not matched to any of the filters, applying the scheme's action to it is
allowed, same to the behavior when no filter exists.
For example, let's assume 1) a filter for allowing anonymous pages and 2)
another filter for rejecting young pages are installed in the order. If a page
of a region that eligible to apply the scheme's action is an anonymous page,
the scheme's action will be applied to the page regardless of whether it is
young or not, since it matches with the first allow-filter. If the page is
not anonymous but young, the scheme's action will not be applied, since the
second reject-filter blocks it. If the page is neither anonymous nor young,
the page will pass through the filters evaluation stage since there is no
matching filter, and the action will be applied to the page.
Note that the action can equally be applied to memory that either explicitly
filter-allowed or filters evaluation stage passed. It means that installing
allow-filters at the end of the list makes no practical change but only
filters-checking overhead.
For efficient handling of filters, some types of filters are handled by the
core layer, while others are handled by operations set. In the latter case,
@ -516,7 +541,7 @@ filter are not counted as the scheme has tried to the region. In contrast, if
a memory regions is filtered by an operations set layer-handled filter, it is
counted as the scheme has tried. This difference affects the statistics.
Below types of filters are currently supported.
Below ``type`` of filters are currently supported.
- anonymous page
- Applied to pages that containing data that not stored in files.