From: SeongJae Park Date: Thu, 9 Jan 2025 17:51:23 +0000 (-0800) Subject: Docs/mm/damon/design: document allow/reject DAMOS filter behaviors X-Git-Tag: v6.14-rc1~77^2~98 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=f477b9b409c03b2c431ad5910f6cd9de773c58c4;p=linux-block.git Docs/mm/damon/design: document allow/reject DAMOS filter behaviors 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 Cc: Jonathan Corbet Signed-off-by: Andrew Morton --- diff --git a/Documentation/mm/damon/design.rst b/Documentation/mm/damon/design.rst index 449eb33688c2..667775bab86c 100644 --- a/Documentation/mm/damon/design.rst +++ b/Documentation/mm/damon/design.rst @@ -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.