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| -rw-r--r-- | Documentation/mm/multigen_lru.rst | 14 | ||||
| -rw-r--r-- | mm/vmscan.c | 4 |
2 files changed, 18 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: diff --git a/mm/vmscan.c b/mm/vmscan.c index a741765896b6..eb9263bf6806 100644 --- a/mm/vmscan.c +++ b/mm/vmscan.c @@ -4569,6 +4569,10 @@ static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc) } } +/****************************************************************************** + * 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 |