Commit c28ac3c7 authored by Yu Zhao's avatar Yu Zhao Committed by Andrew Morton
Browse files

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: 018ee47f ("mm: multi-gen LRU: exploit locality in rmap")
Signed-off-by: default avatarYu Zhao <yuzhao@google.com>
Reported-by: default avatar <syzbot+03fd9b3f71641f0ebf2d@syzkaller.appspotmail.com>
Closes: https://lore.kernel.org/000000000000f9ff00060d14c256@google.com/


Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 4bdd58df

mm/vmscan.c

+9 −4
Original line number Diff line number Diff line
@@ -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++;