This is a note to let you know that I've just added the patch titled
mm: multi-gen LRU: ignore non-leaf pmd_young for force_scan=true
to the 6.11-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-multi-gen-lru-ignore-non-leaf-pmd_young-for-force.patch
and it can be found in the queue-6.11 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 3d088fce5c0e855d74428f888cb999405935c393
Author: Yuanchu Xie <yuanchu@xxxxxxxxxx>
Date: Tue Aug 13 09:37:59 2024 -0700
mm: multi-gen LRU: ignore non-leaf pmd_young for force_scan=true
[ Upstream commit bceeeaed4817ba7ad9013b4116c97220a60fcf7c ]
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 occurs 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 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 occurs 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.
Link: https://lkml.kernel.org/r/20240813163759.742675-1-yuanchu@xxxxxxxxxx
Signed-off-by: Yuanchu Xie <yuanchu@xxxxxxxxxx>
Acked-by: Yu Zhao <yuzhao@xxxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Lance Yang <ioworker0@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Stable-dep-of: ddd6d8e975b1 ("mm: multi-gen LRU: remove MM_LEAF_OLD and MM_NONLEAF_TOTAL stats")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 128f307da6eea..b1f88638c5ab4 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3456,7 +3456,7 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long addr, struct vm_area
goto next;
if (!pmd_trans_huge(pmd[i])) {
- if (should_clear_pmd_young())
+ if (!walk->force_scan && should_clear_pmd_young())
pmdp_test_and_clear_young(vma, addr, pmd + i);
goto next;
}
@@ -3543,7 +3543,7 @@ 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;
