When non-leaf pmd accessed bits are available, MGLRU page table walks can clear the accessed bit and promptly ignore the accessed bit on the pte because it's on a different node, so the walk does not update the generation of said page. When the next scan comes around on the right node, 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 measuring the working set size of a node/memcg.
Since force_scan disables various other optimizations, we check force_scan to ignore the non-leaf pmd accessed bit. Signed-off-by: Yuanchu Xie <[email protected]> --- mm/vmscan.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) 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; -- 2.44.0.396.g6e790dbe36-goog
