btrfs: Add error check for add_to_page_cache_lru

From: Liu Bo <[email protected]>

If add_to_page_cache_lru() returns -EEXIST, it indicates the page that belongs to this page_index has been added and this readahead action can go on to next page.

If add_to_page_cache_lru() returns -ENOMEM, it should break for no memory left.

---
 fs/btrfs/compression.c |   19 ++++++++++++++++---
 1 files changed, 16 insertions(+), 3 deletions(-)

index 1d54c53..1bd4d92 100644
@@ -480,10 +480,23 @@ static noinline int add_ra_bio_pages(struct inode *inode,
 		if (!page)
 			break;
 
-		if (add_to_page_cache_lru(page, mapping, page_index,
-								GFP_NOFS)) {
+		ret = add_to_page_cache_lru(page, mapping, page_index,
+								GFP_NOFS);
+		if (ret) {
 			page_cache_release(page);
-			goto next;
+
+			/*
+			 * -EEXIST indicates the page has been added, so
+			 * it can move on to next page.
+			 */
+			if (ret == -EEXIST) {
+				misses++;
+				if (misses > 4)
+					break;
+				goto next;
+			}
+
+			break;
 		}
 
 		end = last_offset + PAGE_CACHE_SIZE - 1;

1.6.5.2

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All right.

Since Adding a macro may make the whole code harder to read, I add a "goto" to avoid this kind of hard coding style instead.

Thanks.

Liubo