linux-kernel - [PATCH 36/62] page cache: Convert find_get

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Date:   Wed, 22 Nov 2017 13:07:13 -0800
From:   Matthew Wilcox <willy@...radead.org>
To:     linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Matthew Wilcox <mawilcox@...rosoft.com>
Subject: [PATCH 36/62] page cache: Convert find_get_entry to xarray

From: Matthew Wilcox <mawilcox@...rosoft.com>

Slightly simpler and shorter code.

Signed-off-by: Matthew Wilcox <mawilcox@...rosoft.com>
---
 mm/filemap.c | 56 +++++++++++++++++++++-----------------------------------
 1 file changed, 21 insertions(+), 35 deletions(-)

diff --git a/mm/filemap.c b/mm/filemap.c
index f60f22867a1a..2172c9f9efb9 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1391,51 +1391,37 @@ EXPORT_SYMBOL(page_cache_prev_hole);
  */
 struct page *find_get_entry(struct address_space *mapping, pgoff_t offset)
 {
-	void **pagep;
+	XA_STATE(xas, offset);
 	struct page *head, *page;
 
 	rcu_read_lock();
 repeat:
-	page = NULL;
-	pagep = radix_tree_lookup_slot(&mapping->pages, offset);
-	if (pagep) {
-		page = radix_tree_deref_slot(pagep);
-		if (unlikely(!page))
-			goto out;
-		if (radix_tree_exception(page)) {
-			if (radix_tree_deref_retry(page))
-				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.
-			 */
-			goto out;
-		}
+	page = xas_load(&mapping->pages, &xas);
+	if (!page || xa_is_value(page))
+		goto out;
 
-		head = compound_head(page);
-		if (!page_cache_get_speculative(head))
-			goto repeat;
+	head = compound_head(page);
+	if (!page_cache_get_speculative(head))
+		goto repeat;
 
-		/* The page was split under us? */
-		if (compound_head(page) != head) {
-			put_page(head);
-			goto repeat;
-		}
+	/* The page was split under us? */
+	if (compound_head(page) != head) {
+		put_page(head);
+		goto repeat;
+	}
 
-		/*
-		 * Has the page moved?
-		 * This is part of the lockless pagecache protocol. See
-		 * include/linux/pagemap.h for details.
-		 */
-		if (unlikely(page != *pagep)) {
-			put_page(head);
-			goto repeat;
-		}
+	/*
+	 * Has the page moved?
+	 * This is part of the lockless pagecache protocol. See
+	 * include/linux/pagemap.h for details.
+	 */
+	if (unlikely(page != xas_reload(&mapping->pages, &xas))) {
+		put_page(head);
+		goto repeat;
 	}
+
 out:
 	rcu_read_unlock();
-
 	return page;
 }
 EXPORT_SYMBOL(find_get_entry);
-- 
2.15.0