58 lines
2.3 KiB
Diff
58 lines
2.3 KiB
Diff
From 5ddf9d53d375e42af49b744bd7c2f8247c6bce15 Mon Sep 17 00:00:00 2001
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From: "T.J. Alumbaugh" <talumbau@google.com>
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Date: Wed, 18 Jan 2023 00:18:22 +0000
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Subject: [PATCH 13/19] UPSTREAM: mm: multi-gen LRU: section for rmap/PT walk
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feedback
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Add a section for lru_gen_look_around() in the code and the design doc.
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Link: https://lkml.kernel.org/r/20230118001827.1040870-3-talumbau@google.com
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Change-Id: I5097af63f61b3b69ec2abee6cdbdc33c296df213
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Signed-off-by: T.J. Alumbaugh <talumbau@google.com>
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Cc: Yu Zhao <yuzhao@google.com>
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Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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(cherry picked from commit db19a43d9b3a8876552f00f656008206ef9a5efa)
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Bug: 274865848
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Signed-off-by: T.J. Mercier <tjmercier@google.com>
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---
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Documentation/mm/multigen_lru.rst | 14 ++++++++++++++
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mm/vmscan.c | 4 ++++
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2 files changed, 18 insertions(+)
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--- a/Documentation/mm/multigen_lru.rst
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+++ b/Documentation/mm/multigen_lru.rst
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@@ -156,6 +156,20 @@ This time-based approach has the followi
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and memory sizes.
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2. It is more reliable because it is directly wired to the OOM killer.
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+Rmap/PT walk feedback
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+---------------------
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+Searching the rmap for PTEs mapping each page on an LRU list (to test
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+and clear the accessed bit) can be expensive because pages from
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+different VMAs (PA space) are not cache friendly to the rmap (VA
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+space). For workloads mostly using mapped pages, searching the rmap
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+can incur the highest CPU cost in the reclaim path.
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+
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+``lru_gen_look_around()`` exploits spatial locality to reduce the
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+trips into the rmap. It scans the adjacent PTEs of a young PTE and
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+promotes hot pages. If the scan was done cacheline efficiently, it
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+adds the PMD entry pointing to the PTE table to the Bloom filter. This
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+forms a feedback loop between the eviction and the aging.
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+
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Summary
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-------
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The multi-gen LRU can be disassembled into the following parts:
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--- a/mm/vmscan.c
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+++ b/mm/vmscan.c
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@@ -4555,6 +4555,10 @@ static void lru_gen_age_node(struct pgli
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}
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}
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+/******************************************************************************
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+ * rmap/PT walk feedback
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+ ******************************************************************************/
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+
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/*
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* This function exploits spatial locality when shrink_folio_list() walks the
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* rmap. It scans the adjacent PTEs of a young PTE and promotes hot pages. If
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