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    Subject[PATCH v13 25/72] page cache: Convert find_get_pages_range to XArray
    Date
    From: Matthew Wilcox <mawilcox@microsoft.com>

    The 'end' parameter of the xas_for_each iterator avoids a useless
    iteration at the end of the range.

    Signed-off-by: Matthew Wilcox <mawilcox@microsoft.com>
    ---
    mm/filemap.c | 52 +++++++++++++++++++---------------------------------
    1 file changed, 19 insertions(+), 33 deletions(-)

    diff --git a/mm/filemap.c b/mm/filemap.c
    index b49290131e85..019c263bb6be 100644
    --- a/mm/filemap.c
    +++ b/mm/filemap.c
    @@ -1650,64 +1650,50 @@ unsigned find_get_pages_range(struct address_space *mapping, pgoff_t *start,
    pgoff_t end, unsigned int nr_pages,
    struct page **pages)
    {
    - struct radix_tree_iter iter;
    - void **slot;
    + XA_STATE(xas, &mapping->i_pages, *start);
    + struct page *page;
    unsigned ret = 0;

    if (unlikely(!nr_pages))
    return 0;

    rcu_read_lock();
    - radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, *start) {
    - struct page *head, *page;
    -
    - if (iter.index > end)
    - break;
    -repeat:
    - page = radix_tree_deref_slot(slot);
    - if (unlikely(!page))
    + xas_for_each(&xas, page, end) {
    + struct page *head;
    + if (xas_retry(&xas, page))
    continue;
    -
    - if (radix_tree_exception(page)) {
    - if (radix_tree_deref_retry(page)) {
    - slot = radix_tree_iter_retry(&iter);
    - continue;
    - }
    - /*
    - * A shadow entry of a recently evicted page,
    - * or a swap entry from shmem/tmpfs. Skip
    - * over it.
    - */
    + /* Skip over shadow, swap and DAX entries */
    + if (xa_is_value(page))
    continue;
    - }

    head = compound_head(page);
    if (!page_cache_get_speculative(head))
    - goto repeat;
    + goto retry;

    /* The page was split under us? */
    - if (compound_head(page) != head) {
    - put_page(head);
    - goto repeat;
    - }
    + if (compound_head(page) != head)
    + goto put_page;

    /* Has the page moved? */
    - if (unlikely(page != *slot)) {
    - put_page(head);
    - goto repeat;
    - }
    + if (unlikely(page != xas_reload(&xas)))
    + goto put_page;

    pages[ret] = page;
    if (++ret == nr_pages) {
    - *start = pages[ret - 1]->index + 1;
    + *start = page->index + 1;
    goto out;
    }
    + continue;
    +put_page:
    + put_page(head);
    +retry:
    + xas_reset(&xas);
    }

    /*
    * We come here when there is no page beyond @end. We take care to not
    * overflow the index @start as it confuses some of the callers. This
    - * breaks the iteration when there is page at index -1 but that is
    + * breaks the iteration when there is a page at index -1 but that is
    * already broken anyway.
    */
    if (end == (pgoff_t)-1)
    --
    2.17.1
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