From: SeongJae Park Date: Fri, 27 Feb 2026 17:06:20 +0000 (-0800) Subject: mm/damon/core: set quota-score histogram with core filters X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=e7e1a26b8ddf0c8df117cc5b211a81ce635a0613;p=thirdparty%2Flinux.git mm/damon/core: set quota-score histogram with core filters Patch series "mm/damon/core: improve DAMOS quota efficiency for core layer filters". Improve two below problematic behaviors of DAMOS that makes it less efficient when core layer filters are used. DAMOS generates the under-quota regions prioritization-purpose access temperature histogram [1] with only the scheme target access pattern. The DAMOS filters are ignored on the histogram, and this can result in the scheme not applied to eligible regions. For working around this, users had to use separate DAMON contexts. The memory tiering approaches are such examples. DAMOS splits regions that intersect with address filters, so that only filtered-out part of the region is skipped. But, the implementation is skipping the other part of the region that is not filtered out, too. As a result, DAMOS can work slower than expected. Improve the two inefficient behaviors with two patches, respectively. Read the patches for more details about the problem and how those are fixed. This patch (of 2): The histogram for under-quota region prioritization [1] is made for all regions that are eligible for the DAMOS target access pattern. When there are DAMOS filters, the prioritization-threshold access temperature that generated from the histogram could be inaccurate. For example, suppose there are three regions. Each region is 1 GiB. The access temperature of the regions are 100, 50, and 0. And a DAMOS scheme that targets _any_ access temperature with quota 2 GiB is being used. The histogram will look like below: temperature size of regions having >=temperature temperature 0 3 GiB 50 2 GiB 100 1 GiB Based on the histogram and the quota (2 GiB), DAMOS applies the action to only the regions having >=50 temperature. This is all good. Let's suppose the region of temperature 50 is excluded by a DAMOS filter. Regardless of the filter, DAMOS will try to apply the action on only regions having >=50 temperature. Because the region of temperature 50 is filtered out, the action is applied to only the region of temperature 100. Worse yet, suppose the filter is excluding regions of temperature 50 and 100. Then no action is really applied to any region, while the region of temperature 0 is there. People used to work around this by utilizing multiple contexts, instead of the core layer DAMOS filters. For example, DAMON-based memory tiering approaches including the quota auto-tuning based one [2] are using a DAMON context per NUMA node. If the above explained issue is effectively alleviated, those can be configured again to run with single context and DAMOS filters for applying the promotion and demotion to only specific NUMA nodes. Alleviate the problem by checking core DAMOS filters when generating the histogram. The reason to check only core filters is the overhead. While core filters are usually for coarse-grained filtering (e.g., target/address filters for process, NUMA, zone level filtering), operation layer filters are usually for fine-grained filtering (e.g., for anon page). Doing this for operation layer filters would cause significant overhead. There is no known use case that is affected by the operation layer filters-distorted histogram problem, though. Do this for only core filters for now. We will revisit this for operation layer filters in future. We might be able to apply a sort of sampling based operation layer filtering. After this fix is applied, for the first case that there is a DAMOS filter excluding the region of temperature 50, the histogram will be like below: temperature size of regions having >=temperature temperature 0 2 GiB 100 1 GiB And DAMOS will set the temperature threshold as 0, allowing both regions of temperatures 0 and 100 be applied. For the second case that there is a DAMOS filter excluding the regions of temperature 50 and 100, the histogram will be like below: temperature size of regions having >=temperature temperature 0 1 GiB And DAMOS will set the temperature threshold as 0, allowing the region of temperature 0 be applied. [1] 'Prioritization' section of Documentation/mm/damon/design.rst [2] commit 0e1c773b501f ("mm/damon/core: introduce damos quota goal metrics for memory node utilization") Link: https://lkml.kernel.org/r/20260227170623.95384-1-sj@kernel.org Link: https://lkml.kernel.org/r/20260227170623.95384-2-sj@kernel.org Signed-off-by: SeongJae Park Signed-off-by: Andrew Morton --- diff --git a/mm/damon/core.c b/mm/damon/core.c index 0e5ada441b058..722dcb8fff7a1 100644 --- a/mm/damon/core.c +++ b/mm/damon/core.c @@ -2319,6 +2319,8 @@ static void damos_adjust_quota(struct damon_ctx *c, struct damos *s) damon_for_each_region(r, t) { if (!__damos_valid_target(r, s)) continue; + if (damos_core_filter_out(c, t, r, s)) + continue; score = c->ops.get_scheme_score(c, r, s); c->regions_score_histogram[score] += damon_sz_region(r);