From c28ac3c7eb945fee6e20f47d576af68fdff1392a Mon Sep 17 00:00:00 2001
From: Yu Zhao <yuzhao@google.com>
Date: Fri, 22 Dec 2023 21:56:47 -0700
Subject: [PATCH] mm/mglru: skip special VMAs in lru_gen_look_around()
Special VMAs like VM_PFNMAP can contain anon pages from COW. There isn't
much profit in doing lookaround on them. Besides, they can trigger the
pte_special() warning in get_pte_pfn().
Skip them in lru_gen_look_around().
Link: https://lkml.kernel.org/r/20231223045647.1566043-1-yuzhao@google.com
Fixes: 018ee47f1489 ("mm: multi-gen LRU: exploit locality in rmap")
Signed-off-by: Yu Zhao <yuzhao@google.com>
Reported-by: syzbot+03fd9b3f71641f0ebf2d@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/000000000000f9ff00060d14c256@google.com/
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/vmscan.c | 13 +++++++++----
1 file changed, 9 insertions(+), 4 deletions(-)
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 9dd8977de5a22..bba207f41b148 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -3955,6 +3955,7 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
int young = 0;
pte_t *pte = pvmw->pte;
unsigned long addr = pvmw->address;
+ struct vm_area_struct *vma = pvmw->vma;
struct folio *folio = pfn_folio(pvmw->pfn);
bool can_swap = !folio_is_file_lru(folio);
struct mem_cgroup *memcg = folio_memcg(folio);
@@ -3969,11 +3970,15 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
if (spin_is_contended(pvmw->ptl))
return;
+ /* exclude special VMAs containing anon pages from COW */
+ if (vma->vm_flags & VM_SPECIAL)
+ return;
+
/* avoid taking the LRU lock under the PTL when possible */
walk = current->reclaim_state ? current->reclaim_state->mm_walk : NULL;
- start = max(addr & PMD_MASK, pvmw->vma->vm_start);
- end = min(addr | ~PMD_MASK, pvmw->vma->vm_end - 1) + 1;
+ start = max(addr & PMD_MASK, vma->vm_start);
+ end = min(addr | ~PMD_MASK, vma->vm_end - 1) + 1;
if (end - start > MIN_LRU_BATCH * PAGE_SIZE) {
if (addr - start < MIN_LRU_BATCH * PAGE_SIZE / 2)
@@ -3998,7 +4003,7 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
unsigned long pfn;
pte_t ptent = ptep_get(pte + i);
- pfn = get_pte_pfn(ptent, pvmw->vma, addr);
+ pfn = get_pte_pfn(ptent, vma, addr);
if (pfn == -1)
continue;
@@ -4009,7 +4014,7 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
if (!folio)
continue;
- if (!ptep_test_and_clear_young(pvmw->vma, addr, pte + i))
+ if (!ptep_test_and_clear_young(vma, addr, pte + i))
VM_WARN_ON_ONCE(true);
young++;
--
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