diff mbox series

[v1,1/7] mm: multi-gen LRU: ignore non-leaf pmd_young for force_scan=true

Message ID 20240504073011.4000534-2-yuanchu@google.com
State Superseded
Headers show
Series mm: workingset reporting | expand

Commit Message

Yuanchu Xie May 4, 2024, 7:30 a.m. UTC 
When non-leaf pmd accessed bits are available, MGLRU page table walks
can clear the non-leaf pmd accessed bit and ignore the accessed bit on
the pte if it's on a different node, skipping a generation update as
well. If another scan occurrs on the same node as said skipped pte.
the non-leaf pmd accessed bit might remain cleared and the pte accessed
bits won't be checked. While this is sufficient for reclaim-driven
aging, where the goal is to select a reasonably cold page, the access
can be missed when aging proactively for workingset estimation of a of a
node/memcg.

In more detail, get_pfn_folio returns NULL if the folio's nid != node
under scanning, so the page table walk skips processing of said pte. Now
the pmd_young flag on this pmd is cleared, and if none of the pte's are
accessed before another scan occurrs on the folio's node, the pmd_young
check fails and the pte accessed bit is skipped.

Since force_scan disables various other optimizations, we check
force_scan to ignore the non-leaf pmd accessed bit.

Signed-off-by: Yuanchu Xie <yuanchu@google.com>
---
 mm/vmscan.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 4f9c854ce6cc..1a7c7d537db6 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3522,7 +3522,7 @@  static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
 
 		walk->mm_stats[MM_NONLEAF_TOTAL]++;
 
-		if (should_clear_pmd_young()) {
+		if (!walk->force_scan && should_clear_pmd_young()) {
 			if (!pmd_young(val))
 				continue;