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Date: Tue, 3 May 2022 13:17:09 -0700
From: Mike Kravetz <mike.kravetz@...cle.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>,
akpm@...ux-foundation.org
Cc: almasrymina@...gle.com, songmuchun@...edance.com,
linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/3] mm: rmap: Use flush_cache_range() to flush cache
for hugetlb pages
On 4/27/22 03:52, Baolin Wang wrote:
> Now we will use flush_cache_page() to flush cache for anonymous hugetlb
> pages when unmapping or migrating a hugetlb page mapping, but the
> flush_cache_page() only handles a PAGE_SIZE range on some architectures
> (like arm32, arc and so on), which will cause potential cache issues.
> Thus change to use flush_cache_range() to cover the whole size of a
> hugetlb page.
>
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---
> mm/rmap.c | 90 ++++++++++++++++++++++++++++++++++-----------------------------
> 1 file changed, 48 insertions(+), 42 deletions(-)
>
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 4f0d115..6fdd198 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1528,13 +1528,7 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
> anon_exclusive = folio_test_anon(folio) &&
> PageAnonExclusive(subpage);
>
> - if (folio_test_hugetlb(folio) && !folio_test_anon(folio)) {
> - /*
> - * To call huge_pmd_unshare, i_mmap_rwsem must be
> - * held in write mode. Caller needs to explicitly
> - * do this outside rmap routines.
> - */
> - VM_BUG_ON(!(flags & TTU_RMAP_LOCKED));
> + if (folio_test_hugetlb(folio)) {
> /*
> * huge_pmd_unshare may unmap an entire PMD page.
> * There is no way of knowing exactly which PMDs may
> @@ -1544,22 +1538,31 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
> */
> flush_cache_range(vma, range.start, range.end);
>
> - if (huge_pmd_unshare(mm, vma, &address, pvmw.pte)) {
> - flush_tlb_range(vma, range.start, range.end);
> - mmu_notifier_invalidate_range(mm, range.start,
> - range.end);
> -
> + if (!folio_test_anon(folio)) {
> /*
> - * The ref count of the PMD page was dropped
> - * which is part of the way map counting
> - * is done for shared PMDs. Return 'true'
> - * here. When there is no other sharing,
> - * huge_pmd_unshare returns false and we will
> - * unmap the actual page and drop map count
> - * to zero.
> + * To call huge_pmd_unshare, i_mmap_rwsem must be
> + * held in write mode. Caller needs to explicitly
> + * do this outside rmap routines.
> */
> - page_vma_mapped_walk_done(&pvmw);
> - break;
> + VM_BUG_ON(!(flags & TTU_RMAP_LOCKED));
> +
> + if (huge_pmd_unshare(mm, vma, &address, pvmw.pte)) {
> + flush_tlb_range(vma, range.start, range.end);
> + mmu_notifier_invalidate_range(mm, range.start,
> + range.end);
> +
> + /*
> + * The ref count of the PMD page was dropped
> + * which is part of the way map counting
> + * is done for shared PMDs. Return 'true'
> + * here. When there is no other sharing,
> + * huge_pmd_unshare returns false and we will
> + * unmap the actual page and drop map count
> + * to zero.
> + */
> + page_vma_mapped_walk_done(&pvmw);
> + break;
> + }
> }
> } else {
> flush_cache_page(vma, address, pte_pfn(*pvmw.pte));
> @@ -1885,13 +1888,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
> anon_exclusive = folio_test_anon(folio) &&
> PageAnonExclusive(subpage);
>
> - if (folio_test_hugetlb(folio) && !folio_test_anon(folio)) {
> - /*
> - * To call huge_pmd_unshare, i_mmap_rwsem must be
> - * held in write mode. Caller needs to explicitly
> - * do this outside rmap routines.
> - */
> - VM_BUG_ON(!(flags & TTU_RMAP_LOCKED));
> + if (folio_test_hugetlb(folio)) {
> /*
> * huge_pmd_unshare may unmap an entire PMD page.
> * There is no way of knowing exactly which PMDs may
> @@ -1901,22 +1898,31 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
> */
> flush_cache_range(vma, range.start, range.end);
>
> - if (huge_pmd_unshare(mm, vma, &address, pvmw.pte)) {
> - flush_tlb_range(vma, range.start, range.end);
> - mmu_notifier_invalidate_range(mm, range.start,
> - range.end);
> -
> + if (!folio_test_anon(folio)) {
> /*
> - * The ref count of the PMD page was dropped
> - * which is part of the way map counting
> - * is done for shared PMDs. Return 'true'
> - * here. When there is no other sharing,
> - * huge_pmd_unshare returns false and we will
> - * unmap the actual page and drop map count
> - * to zero.
> + * To call huge_pmd_unshare, i_mmap_rwsem must be
> + * held in write mode. Caller needs to explicitly
> + * do this outside rmap routines.
> */
> - page_vma_mapped_walk_done(&pvmw);
> - break;
> + VM_BUG_ON(!(flags & TTU_RMAP_LOCKED));
> +
> + if (huge_pmd_unshare(mm, vma, &address, pvmw.pte)) {
> + flush_tlb_range(vma, range.start, range.end);
> + mmu_notifier_invalidate_range(mm, range.start,
> + range.end);
> +
> + /*
> + * The ref count of the PMD page was dropped
> + * which is part of the way map counting
> + * is done for shared PMDs. Return 'true'
> + * here. When there is no other sharing,
> + * huge_pmd_unshare returns false and we will
> + * unmap the actual page and drop map count
> + * to zero.
> + */
> + page_vma_mapped_walk_done(&pvmw);
> + break;
> + }
> }
> } else {
> flush_cache_page(vma, address, pte_pfn(*pvmw.pte));
Thanks,
The code looks fine. It is unfortunate that we need so many levels of
indenting and exceed 80 columns. But, that is OK.
Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
I see you have a followup series to address the call to ptep_clear_flush()
for hugetlb pages not unmapped via huge_pmd_share and will take a look at
that soon.
--
Mike Kravetz
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