[PATCH] mm: bail out when the PMD has been set in bloom filter

[zhaoyang.huang]

From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>

There are two reasons to have the recorded PMD bail out from doing
the following iteration
1. It is worth of doing such a trade off thing in terms of reclaiming
efficiency as test_bloom_filter only consume 20~30 instructions in modern
processors(25 instructions in ARM64).
2. The PMD needs to accumulate young pages until aging happens while the
new arrived folio reference checking under current max_seq refuse to do so
which will affect carrying hot PMDs to new generation.

Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
---
 mm/vmscan.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 9d900be478ea..e50e98291d0d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4227,6 +4227,10 @@ bool lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
 	/* avoid taking the LRU lock under the PTL when possible */
 	walk = current->reclaim_state ? current->reclaim_state->mm_walk : NULL;
 
+	/* may the pmd has been set in bloom filter */
+	if (test_bloom_filter(mm_state, max_seq, pvmw->pmd))
+		return true;
+
 	start = max(addr & PMD_MASK, vma->vm_start);
 	end = min(addr | ~PMD_MASK, vma->vm_end - 1) + 1;
 
-- 
2.25.1