[PATCH v7 23/24] mm: Document why we don't set PageReadahead

[Matthew Wilcox]

From: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>

If the page is already in cache, we don't set PageReadahead on it.

Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
---
 mm/readahead.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index 453ef146de83..bbe7208fcc2d 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -196,9 +196,12 @@ void page_cache_readahead_unbounded(struct address_space *mapping,
 
 		if (page && !xa_is_value(page)) {
 			/*
-			 * Page already present?  Kick off the current batch of
-			 * contiguous pages before continuing with the next
-			 * batch.
+			 * Page already present?  Kick off the current batch
+			 * of contiguous pages before continuing with the
+			 * next batch.  This page may be the one we would
+			 * have intended to mark as Readahead, but we don't
+			 * have a stable reference to this page, and it's
+			 * not worth getting one just for that.
 			 */
 			read_pages(&rac, &page_pool);
 			continue;
-- 
2.25.0