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    Subject[PATCH v5 09/26] mm: Introduce ZAP_FLAG_SKIP_SWAP
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    Firstly, the comment in zap_pte_range() is misleading because it checks against
    details rather than check_mappings, so it's against what the code did.

    Meanwhile, it's confusing too on not explaining why passing in the details
    pointer would mean to skip all swap entries. New user of zap_details could
    very possibly miss this fact if they don't read deep until zap_pte_range()
    because there's no comment at zap_details talking about it at all, so swap
    entries could be errornously skipped without being noticed.

    This partly reverts 3e8715fdc03e ("mm: drop zap_details::check_swap_entries"),
    but introduce ZAP_FLAG_SKIP_SWAP flag, which means the opposite of previous
    "details" parameter: the caller should explicitly set this to skip swap
    entries, otherwise swap entries will always be considered (which is still the
    major case here).

    Cc: Kirill A. Shutemov <kirill@shutemov.name>
    Reviewed-by: Alistair Popple <apopple@nvidia.com>
    Signed-off-by: Peter Xu <peterx@redhat.com>
    ---
    include/linux/mm.h | 12 ++++++++++++
    mm/memory.c | 8 +++++---
    2 files changed, 17 insertions(+), 3 deletions(-)

    diff --git a/include/linux/mm.h b/include/linux/mm.h
    index 26088174daab..62a75e4414e3 100644
    --- a/include/linux/mm.h
    +++ b/include/linux/mm.h
    @@ -1717,6 +1717,8 @@ extern void user_shm_unlock(size_t, struct ucounts *);

    /* Whether to check page->mapping when zapping */
    #define ZAP_FLAG_CHECK_MAPPING BIT(0)
    +/* Whether to skip zapping swap entries */
    +#define ZAP_FLAG_SKIP_SWAP BIT(1)

    /*
    * Parameter block passed down to zap_pte_range in exceptional cases.
    @@ -1740,6 +1742,16 @@ zap_skip_check_mapping(struct zap_details *details, struct page *page)
    return details->zap_mapping != page_rmapping(page);
    }

    +/* Return true if skip swap entries, false otherwise */
    +static inline bool
    +zap_skip_swap(struct zap_details *details)
    +{
    + if (!details)
    + return false;
    +
    + return details->zap_flags & ZAP_FLAG_SKIP_SWAP;
    +}
    +
    struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
    pte_t pte);
    struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr,
    diff --git a/mm/memory.c b/mm/memory.c
    index 2a5a6650f069..d6b1adbf29e4 100644
    --- a/mm/memory.c
    +++ b/mm/memory.c
    @@ -1379,8 +1379,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
    continue;
    }

    - /* If details->check_mapping, we leave swap entries. */
    - if (unlikely(details))
    + if (unlikely(zap_skip_swap(details)))
    continue;

    if (!non_swap_entry(entry))
    @@ -3379,7 +3378,10 @@ void unmap_mapping_pages(struct address_space *mapping, pgoff_t start,
    pgoff_t nr, bool even_cows)
    {
    pgoff_t first_index = start, last_index = start + nr - 1;
    - struct zap_details details = { .zap_mapping = mapping };
    + struct zap_details details = {
    + .zap_mapping = mapping,
    + .zap_flags = ZAP_FLAG_SKIP_SWAP,
    + };

    if (!even_cows)
    details.zap_flags |= ZAP_FLAG_CHECK_MAPPING;
    --
    2.31.1
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