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Date: Wed, 4 May 2022 10:49:23 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Mike Kravetz <mike.kravetz@...cle.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 5/4/2022 4:17 AM, Mike Kravetz wrote:
> 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.
I'll do a cleanup to make it more readable with factoring the hugetlb
case into a new function after the fix series[1].
[1]
https://lore.kernel.org/linux-arm-kernel/20220503120343.6264e126@thinkpad/T/
>
> 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.
Thanks.
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