mm: split ->readpages calls to avoid non-contiguous pages lists
That way file systems don't have to go spotting for non-contiguous pages
and work around them. It also kicks off I/O earlier, allowing it to
finish earlier and reduce latency.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
diff --git a/mm/readahead.c b/mm/readahead.c
index fa4d4b7..e273f0d 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -140,8 +140,8 @@ static int read_pages(struct address_space *mapping, struct file *filp,
}
/*
- * __do_page_cache_readahead() actually reads a chunk of disk. It allocates all
- * the pages first, then submits them all for I/O. This avoids the very bad
+ * __do_page_cache_readahead() actually reads a chunk of disk. It allocates
+ * the pages first, then submits them for I/O. This avoids the very bad
* behaviour which would occur if page allocations are causing VM writeback.
* We really don't want to intermingle reads and writes like that.
*
@@ -177,8 +177,18 @@ unsigned int __do_page_cache_readahead(struct address_space *mapping,
rcu_read_lock();
page = radix_tree_lookup(&mapping->i_pages, page_offset);
rcu_read_unlock();
- if (page && !radix_tree_exceptional_entry(page))
+ if (page && !radix_tree_exceptional_entry(page)) {
+ /*
+ * Page already present? Kick off the current batch of
+ * contiguous pages before continuing with the next
+ * batch.
+ */
+ if (nr_pages)
+ read_pages(mapping, filp, &page_pool, nr_pages,
+ gfp_mask);
+ nr_pages = 0;
continue;
+ }
page = __page_cache_alloc(gfp_mask);
if (!page)
