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

Commit Message

Matthew Wilcox July 15, 2021, 3:36 a.m. UTC

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) <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
---
 mm/filemap.c | 35 ++++++++++++++---------------------
 1 file changed, 14 insertions(+), 21 deletions(-)

Comments

David Howells Aug. 10, 2021, 10 p.m. UTC | #1

Matthew Wilcox (Oracle) <[e-mail]> wrote:

> 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) <[e-mail]>
> Reviewed-by: Christoph Hellwig <[e-mail]>

Reviewed-by: David Howells <[e-mail]>

Vlastimil Babka Aug. 12, 2021, 5:37 p.m. UTC | #2

On 7/15/21 5:36 AM, Matthew Wilcox (Oracle) wrote:
> 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) <[e-mail]>
> Reviewed-by: Christoph Hellwig <[e-mail]>

Acked-by: Vlastimil Babka <[e-mail]>

Patch

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;
 }
 
 /**