Re: [PATCH 2/3] mm: rmap: Fix CONT-PTE/PMD size hugetlb issue when migration
From: Mike Kravetz <hidden>
Date: 2022-05-05 23:54:49
Also in:
linux-arch, linux-arm-kernel, linux-mips, linux-mm, linux-s390, linux-sh, lkml, sparclinux
On 4/29/22 01:14, Baolin Wang wrote:
On some architectures (like ARM64), it can support CONT-PTE/PMD size hugetlb, which means it can support not only PMD/PUD size hugetlb: 2M and 1G, but also CONT-PTE/PMD size: 64K and 32M if a 4K page size specified.
<snip>
quoted hunk ↗ jump to hunk
diff --git a/mm/rmap.c b/mm/rmap.c index 6fdd198..7cf2408 100644 --- a/mm/rmap.c +++ b/mm/rmap.c@@ -1924,13 +1924,15 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, break; } } + + /* Nuke the hugetlb page table entry */ + pteval = huge_ptep_clear_flush(vma, address, pvmw.pte); } else { flush_cache_page(vma, address, pte_pfn(*pvmw.pte)); + /* Nuke the page table entry. */ + pteval = ptep_clear_flush(vma, address, pvmw.pte); }
On arm64 with CONT-PTE/PMD the returned pteval will have dirty or young set if ANY of the PTE/PMDs had dirty or young set.
quoted hunk ↗ jump to hunk
- /* Nuke the page table entry. */ - pteval = ptep_clear_flush(vma, address, pvmw.pte); - /* Set the dirty flag on the folio now the pte is gone. */ if (pte_dirty(pteval)) folio_mark_dirty(folio);@@ -2015,7 +2017,10 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, pte_t swp_pte; if (arch_unmap_one(mm, vma, address, pteval) < 0) { - set_pte_at(mm, address, pvmw.pte, pteval); + if (folio_test_hugetlb(folio)) + set_huge_pte_at(mm, address, pvmw.pte, pteval);
And, we will use that pteval for ALL the PTE/PMDs here. So, we would set the dirty or young bit in ALL PTE/PMDs. Could that cause any issues? May be more of a question for the arm64 people. -- Mike Kravetz