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    Subject[PATCH v5 08/26] mm: Introduce zap_details.zap_flags
    Date
    Instead of trying to introduce one variable for every new zap_details fields,
    let's introduce a flag so that it can start to encode true/false informations.

    Let's start to use this flag first to clean up the only check_mapping variable.
    Firstly, the name "check_mapping" implies this is a "boolean", but actually it
    stores the mapping inside, just in a way that it won't be set if we don't want
    to check the mapping.

    To make things clearer, introduce the 1st zap flag ZAP_FLAG_CHECK_MAPPING, so
    that we only check against the mapping if this bit set. At the same time, we
    can rename check_mapping into zap_mapping and set it always.

    Since at it, introduce another helper zap_check_mapping_skip() and use it in
    zap_pte_range() properly.

    Some old comments have been removed in zap_pte_range() because they're
    duplicated, and since now we're with ZAP_FLAG_CHECK_MAPPING flag, it'll be very
    easy to grep this information by simply grepping the flag.

    It'll also make life easier when we want to e.g. pass in zap_flags into the
    callers like unmap_mapping_pages() (instead of adding new booleans besides the
    even_cows parameter).

    Signed-off-by: Peter Xu <peterx@redhat.com>
    ---
    include/linux/mm.h | 19 ++++++++++++++++++-
    mm/memory.c | 34 ++++++++++------------------------
    2 files changed, 28 insertions(+), 25 deletions(-)

    diff --git a/include/linux/mm.h b/include/linux/mm.h
    index 795b3cd643ca..26088174daab 100644
    --- a/include/linux/mm.h
    +++ b/include/linux/mm.h
    @@ -1715,14 +1715,31 @@ static inline bool can_do_mlock(void) { return false; }
    extern int user_shm_lock(size_t, struct ucounts *);
    extern void user_shm_unlock(size_t, struct ucounts *);

    +/* Whether to check page->mapping when zapping */
    +#define ZAP_FLAG_CHECK_MAPPING BIT(0)
    +
    /*
    * Parameter block passed down to zap_pte_range in exceptional cases.
    */
    struct zap_details {
    - struct address_space *check_mapping; /* Check page->mapping if set */
    + struct address_space *zap_mapping;
    struct page *single_page; /* Locked page to be unmapped */
    + unsigned long zap_flags;
    };

    +/* Return true if skip zapping this page, false otherwise */
    +static inline bool
    +zap_skip_check_mapping(struct zap_details *details, struct page *page)
    +{
    + if (!details || !page)
    + return false;
    +
    + if (!(details->zap_flags & ZAP_FLAG_CHECK_MAPPING))
    + return false;
    +
    + return details->zap_mapping != page_rmapping(page);
    +}
    +
    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 4c269d7b3d83..2a5a6650f069 100644
    --- a/mm/memory.c
    +++ b/mm/memory.c
    @@ -1333,16 +1333,8 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
    struct page *page;

    page = vm_normal_page(vma, addr, ptent);
    - if (unlikely(details) && page) {
    - /*
    - * unmap_shared_mapping_pages() wants to
    - * invalidate cache without truncating:
    - * unmap shared but keep private pages.
    - */
    - if (details->check_mapping &&
    - details->check_mapping != page_rmapping(page))
    - continue;
    - }
    + if (unlikely(zap_skip_check_mapping(details, page)))
    + continue;
    ptent = ptep_get_and_clear_full(mm, addr, pte,
    tlb->fullmm);
    tlb_remove_tlb_entry(tlb, pte, addr);
    @@ -1375,17 +1367,8 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
    is_device_exclusive_entry(entry)) {
    struct page *page = pfn_swap_entry_to_page(entry);

    - if (unlikely(details && details->check_mapping)) {
    - /*
    - * unmap_shared_mapping_pages() wants to
    - * invalidate cache without truncating:
    - * unmap shared but keep private pages.
    - */
    - if (details->check_mapping !=
    - page_rmapping(page))
    - continue;
    - }
    -
    + if (unlikely(zap_skip_check_mapping(details, page)))
    + continue;
    pte_clear_not_present_full(mm, addr, pte, tlb->fullmm);
    rss[mm_counter(page)]--;

    @@ -3369,8 +3352,9 @@ void unmap_mapping_page(struct page *page)
    first_index = page->index;
    last_index = page->index + thp_nr_pages(page) - 1;

    - details.check_mapping = mapping;
    + details.zap_mapping = mapping;
    details.single_page = page;
    + details.zap_flags = ZAP_FLAG_CHECK_MAPPING;

    i_mmap_lock_write(mapping);
    if (unlikely(!RB_EMPTY_ROOT(&mapping->i_mmap.rb_root)))
    @@ -3395,9 +3379,11 @@ 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 = { };
    + struct zap_details details = { .zap_mapping = mapping };
    +
    + if (!even_cows)
    + details.zap_flags |= ZAP_FLAG_CHECK_MAPPING;

    - details.check_mapping = even_cows ? NULL : mapping;
    if (last_index < first_index)
    last_index = ULONG_MAX;

    --
    2.31.1
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