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author | T.J. Alumbaugh <talumbau@google.com> | 2023-01-18 03:18:24 +0300 |
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committer | Andrew Morton <akpm@linux-foundation.org> | 2023-02-03 09:33:27 +0300 |
commit | 36c7b4db7c942ae9e1b111f0c6b468c8b2e33842 (patch) | |
tree | db10757d8ae91e1ee93b3c2b272adfb934c2fa66 /Documentation/mm | |
parent | ccbbbb85945d8f0255aa9dbc1b617017e2294f2c (diff) | |
download | linux-36c7b4db7c942ae9e1b111f0c6b468c8b2e33842.tar.xz |
mm: multi-gen LRU: section for memcg LRU
Move memcg LRU code into a dedicated section. Improve the design doc to
outline its architecture.
Link: https://lkml.kernel.org/r/20230118001827.1040870-5-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 | 33 |
1 files changed, 32 insertions, 1 deletions
diff --git a/Documentation/mm/multigen_lru.rst b/Documentation/mm/multigen_lru.rst index 770b5d539856..5f1f6ecbb79b 100644 --- a/Documentation/mm/multigen_lru.rst +++ b/Documentation/mm/multigen_lru.rst @@ -186,9 +186,40 @@ is false positive, the cost is an additional scan of a range of PTEs, which may yield hot pages anyway. Parameters of the filter itself can control the false positive rate in the limit. +Memcg LRU +--------- +An memcg LRU is a per-node LRU of memcgs. It is also an LRU of LRUs, +since each node and memcg combination has an LRU of folios (see +``mem_cgroup_lruvec()``). Its goal is to improve the scalability of +global reclaim, which is critical to system-wide memory overcommit in +data centers. Note that memcg LRU only applies to global reclaim. + +The basic structure of an memcg LRU can be understood by an analogy to +the active/inactive LRU (of folios): + +1. It has the young and the old (generations), i.e., the counterparts + to the active and the inactive; +2. The increment of ``max_seq`` triggers promotion, i.e., the + counterpart to activation; +3. Other events trigger similar operations, e.g., offlining an memcg + triggers demotion, i.e., the counterpart to deactivation. + +In terms of global reclaim, it has two distinct features: + +1. Sharding, which allows each thread to start at a random memcg (in + the old generation) and improves parallelism; +2. Eventual fairness, which allows direct reclaim to bail out at will + and reduces latency without affecting fairness over some time. + +In terms of traversing memcgs during global reclaim, it improves the +best-case complexity from O(n) to O(1) and does not affect the +worst-case complexity O(n). Therefore, on average, it has a sublinear +complexity. + Summary ------- -The multi-gen LRU can be disassembled into the following parts: +The multi-gen LRU (of folios) can be disassembled into the following +parts: * Generations * Rmap walks |