The patch titled Subject: mm/mglru: skip special VMAs in lru_gen_look_around() has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-mglru-skip-special-vmas-in-lru_gen_look_around.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Yu Zhao yuzhao@google.com Subject: mm/mglru: skip special VMAs in lru_gen_look_around() Date: Fri, 22 Dec 2023 21:56:47 -0700

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(-)

--- a/mm/vmscan.c~mm-mglru-skip-special-vmas-in-lru_gen_look_around +++ a/mm/vmscan.c @@ -3955,6 +3955,7 @@ void lru_gen_look_around(struct page_vma 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 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 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 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++; _

Patches currently in -mm which might be from yuzhao@google.com are

mm-mglru-skip-special-vmas-in-lru_gen_look_around.patch