[PATCH v14 087/138] mm/filemap: Convert mapping_get_entry to return a folio

Matthew Wilcox (Oracle)
2021-07-15T04:47:59Z

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