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| author | T.J. Alumbaugh <talumbau@google.com> | 2023-01-18 00:18:22 +0000 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2023-02-02 22:33:26 -0800 |
| commit | db19a43d9b3a8876552f00f656008206ef9a5efa (patch) | |
| tree | 292b4d2091feacee998b664eeac0e5a3fdfc20be /Documentation/mm | |
| parent | 7b8144e63d84716f16a1b929e0c7e03ae5c4d5c1 (diff) | |
| download | linux-db19a43d9b3a8876552f00f656008206ef9a5efa.tar.gz linux-db19a43d9b3a8876552f00f656008206ef9a5efa.tar.bz2 linux-db19a43d9b3a8876552f00f656008206ef9a5efa.zip | |
mm: multi-gen LRU: section for rmap/PT walk feedback
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@google.com
Signed-off-by: T.J. Alumbaugh <talumbau@google.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'Documentation/mm')
| -rw-r--r-- | Documentation/mm/multigen_lru.rst | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/Documentation/mm/multigen_lru.rst b/Documentation/mm/multigen_lru.rst index 6e1483e70fdc..bd988a142bc2 100644 --- a/Documentation/mm/multigen_lru.rst +++ b/Documentation/mm/multigen_lru.rst @@ -156,6 +156,20 @@ This time-based approach has the following advantages: 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: |