[PATCH v6 04/19] mm: Rearrange readahead loop

Matthew Wilcox
2020-02-17T18:47:14Z

From: "Matthew Wilcox (Oracle)" <willy@infradead.org>

Move the declaration of 'page' to inside the loop and move the 'kick
off a fresh batch' code to the end of the function for easier use in
subsequent patches.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
mm/readahead.c | 21 +++++++++++++--------
1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/mm/readahead.c b/mm/readahead.c
index 15329309231f..3eca59c43a45 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -154,7 +154,6 @@ void __do_page_cache_readahead(struct address_space *mapping,
unsigned long lookahead_size)
{
struct inode *inode = mapping->host;
- struct page *page;
unsigned long end_index; /* The last page we want to read */
LIST_HEAD(page_pool);
int page_idx;
@@ -175,6 +174,7 @@ void __do_page_cache_readahead(struct address_space *mapping,
* Preallocate as many pages as we will need.
*/
for (page_idx = 0; page_idx < nr_to_read; page_idx++) {
+ struct page *page;
pgoff_t page_offset = offset + page_idx;

if (page_offset > end_index)
@@ -183,14 +183,14 @@ void __do_page_cache_readahead(struct address_space *mapping,
page = xa_load(&mapping->i_pages, page_offset);
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.
*/
- if (readahead_count(&rac))
- read_pages(&rac, &page_pool, gfp_mask);
- rac._nr_pages = 0;
- continue;
+ goto read;
}

page = __page_cache_alloc(gfp_mask);
@@ -201,6 +201,11 @@ void __do_page_cache_readahead(struct address_space *mapping,
if (page_idx == nr_to_read - lookahead_size)
SetPageReadahead(page);
rac._nr_pages++;
+ continue;
+read:
+ if (readahead_count(&rac))
+ read_pages(&rac, &page_pool, gfp_mask);
+ rac._nr_pages = 0;
}

/*
--
2.25.0