The patch titled
Subject: mm: multi-gen LRU: section for rmap/PT walk feedback
has been added to the -mm mm-unstable branch. Its filename is
mm-multi-gen-lru-section-for-rmap-pt-walk-feedback.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-multi-gen-lru-section-for-rmap-pt-walk-feedback.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: "T.J. Alumbaugh" <talumbau@xxxxxxxxxx>
Subject: mm: multi-gen LRU: section for rmap/PT walk feedback
Date: Wed, 18 Jan 2023 00:18:22 +0000
Add a section for lru_gen_look_around() in the code and the design doc.
Link: https://lkml.kernel.org/r/20230118001827.1040870-3-talumbau@xxxxxxxxxx
Signed-off-by: T.J. Alumbaugh <talumbau@xxxxxxxxxx>
Cc: Yu Zhao <yuzhao@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/Documentation/mm/multigen_lru.rst~mm-multi-gen-lru-section-for-rmap-pt-walk-feedback
+++ a/Documentation/mm/multigen_lru.rst
@@ -156,6 +156,20 @@ This time-based approach has the followi
and memory sizes.
2. It is more reliable because it is directly wired to the OOM killer.
+Rmap/PT walk feedback
+---------------------
+Searching the rmap for PTEs mapping each page on an LRU list (to test
+and clear the accessed bit) can be expensive because pages from
+different VMAs (PA space) are not cache friendly to the rmap (VA
+space). For workloads mostly using mapped pages, searching the rmap
+can incur the highest CPU cost in the reclaim path.
+
+``lru_gen_look_around()`` exploits spatial locality to reduce the
+trips into the rmap. It scans the adjacent PTEs of a young PTE and
+promotes hot pages. If the scan was done cacheline efficiently, it
+adds the PMD entry pointing to the PTE table to the Bloom filter. This
+forms a feedback loop between the eviction and the aging.
+
Summary
-------
The multi-gen LRU can be disassembled into the following parts:
--- a/mm/vmscan.c~mm-multi-gen-lru-section-for-rmap-pt-walk-feedback
+++ a/mm/vmscan.c
@@ -4569,6 +4569,10 @@ static void lru_gen_age_node(struct pgli
}
}
+/******************************************************************************
+ * rmap/PT walk feedback
+ ******************************************************************************/
+
/*
* This function exploits spatial locality when shrink_folio_list() walks the
* rmap. It scans the adjacent PTEs of a young PTE and promotes hot pages. If
_
Patches currently in -mm which might be from talumbau@xxxxxxxxxx are
mm-multi-gen-lru-section-for-working-set-protection.patch
mm-multi-gen-lru-section-for-rmap-pt-walk-feedback.patch
mm-multi-gen-lru-section-for-bloom-filters.patch
mm-multi-gen-lru-section-for-memcg-lru.patch
mm-multi-gen-lru-improve-lru_gen_exit_memcg.patch
mm-multi-gen-lru-improve-walk_pmd_range.patch
mm-multi-gen-lru-simplify-lru_gen_look_around.patch
