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    Subject[PATCH v14 087/138] mm/filemap: Convert mapping_get_entry to return a folio
    Date
    The pagecache only contains folios, so indicate that this is definitely
    not a tail page. Shrinks mapping_get_entry() by 56 bytes, but grows
    pagecache_get_page() by 21 bytes as gcc makes slightly different hot/cold
    code decisions. A net reduction of 35 bytes of text.

    Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    Reviewed-by: Christoph Hellwig <hch@lst.de>
    ---
    mm/filemap.c | 35 ++++++++++++++---------------------
    1 file changed, 14 insertions(+), 21 deletions(-)

    diff --git a/mm/filemap.c b/mm/filemap.c
    index 4e34383fd894..85a457c7b7a7 100644
    --- a/mm/filemap.c
    +++ b/mm/filemap.c
    @@ -1755,49 +1755,42 @@ EXPORT_SYMBOL(page_cache_prev_miss);
    * @mapping: the address_space to search
    * @index: The page cache index.
    *
    - * Looks up the page cache slot at @mapping & @index. If there is a
    - * page cache page, the head page is returned with an increased refcount.
    + * Looks up the page cache entry at @mapping & @index. If it is a folio,
    + * it is returned with an increased refcount. If it is a shadow entry
    + * of a previously evicted folio, or a swap entry from shmem/tmpfs,
    + * it is returned without further action.
    *
    - * If the slot holds a shadow entry of a previously evicted page, or a
    - * swap entry from shmem/tmpfs, it is returned.
    - *
    - * Return: The head page or shadow entry, %NULL if nothing is found.
    + * Return: The folio, swap or shadow entry, %NULL if nothing is found.
    */
    -static struct page *mapping_get_entry(struct address_space *mapping,
    - pgoff_t index)
    +static void *mapping_get_entry(struct address_space *mapping, pgoff_t index)
    {
    XA_STATE(xas, &mapping->i_pages, index);
    - struct page *page;
    + struct folio *folio;

    rcu_read_lock();
    repeat:
    xas_reset(&xas);
    - page = xas_load(&xas);
    - if (xas_retry(&xas, page))
    + folio = xas_load(&xas);
    + if (xas_retry(&xas, folio))
    goto repeat;
    /*
    * A shadow entry of a recently evicted page, or a swap entry from
    * shmem/tmpfs. Return it without attempting to raise page count.
    */
    - if (!page || xa_is_value(page))
    + if (!folio || xa_is_value(folio))
    goto out;

    - if (!page_cache_get_speculative(page))
    + if (!folio_try_get_rcu(folio))
    goto repeat;

    - /*
    - * Has the page moved or been split?
    - * This is part of the lockless pagecache protocol. See
    - * include/linux/pagemap.h for details.
    - */
    - if (unlikely(page != xas_reload(&xas))) {
    - put_page(page);
    + if (unlikely(folio != xas_reload(&xas))) {
    + folio_put(folio);
    goto repeat;
    }
    out:
    rcu_read_unlock();

    - return page;
    + return folio;
    }

    /**
    --
    2.30.2
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