mm/readahead: make ondemand_readahead take a readahead_control

Make ondemand_readahead() take a readahead_control struct in preparation
for making do_sync_mmap_readahead() pass down an RAC struct.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Eric Biggers <ebiggers@google.com>
Link: https://lkml.kernel.org/r/20200903140844.14194-6-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/readahead.c

@@ -431,15 +431,14 @@ static int try_context_readahead(struct address_space *mapping,
 /*
  * A minimal readahead algorithm for trivial sequential/random reads.
  */
-static void ondemand_readahead(struct address_space *mapping,
-		struct file_ra_state *ra, struct file *file,
-		bool hit_readahead_marker, pgoff_t index,
+static void ondemand_readahead(struct readahead_control *ractl,
+		struct file_ra_state *ra, bool hit_readahead_marker,
 		unsigned long req_size)
 {
-	DEFINE_READAHEAD(ractl, file, mapping, index);
-	struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
+	struct backing_dev_info *bdi = inode_to_bdi(ractl->mapping->host);
 	unsigned long max_pages = ra->ra_pages;
 	unsigned long add_pages;
+	unsigned long index = readahead_index(ractl);
 	pgoff_t prev_index;
 
 	/*
@@ -477,7 +476,8 @@ static void ondemand_readahead(struct address_space *mapping,
 		pgoff_t start;
 
 		rcu_read_lock();
-		start = page_cache_next_miss(mapping, index + 1, max_pages);
+		start = page_cache_next_miss(ractl->mapping, index + 1,
+				max_pages);
 		rcu_read_unlock();
 
 		if (!start || start - index > max_pages)
@@ -510,14 +510,15 @@ static void ondemand_readahead(struct address_space *mapping,
 	 * Query the page cache and look for the traces(cached history pages)
 	 * that a sequential stream would leave behind.
 	 */
-	if (try_context_readahead(mapping, ra, index, req_size, max_pages))
+	if (try_context_readahead(ractl->mapping, ra, index, req_size,
+			max_pages))
 		goto readit;
 
 	/*
 	 * standalone, small random read
 	 * Read as is, and do not pollute the readahead state.
 	 */
-	do_page_cache_ra(&ractl, req_size, 0);
+	do_page_cache_ra(ractl, req_size, 0);
 	return;
 
 initial_readahead:
@@ -543,8 +544,8 @@ readit:
 		}
 	}
 
-	ractl._index = ra->start;
-	do_page_cache_ra(&ractl, ra->size, ra->async_size);
+	ractl->_index = ra->start;
+	do_page_cache_ra(ractl, ra->size, ra->async_size);
 }
 
 /**
@@ -564,6 +565,8 @@ void page_cache_sync_readahead(struct address_space *mapping,
 			       struct file_ra_state *ra, struct file *filp,
 			       pgoff_t index, unsigned long req_count)
 {
+	DEFINE_READAHEAD(ractl, filp, mapping, index);
+
 	/* no read-ahead */
 	if (!ra->ra_pages)
 		return;
@@ -578,7 +581,7 @@ void page_cache_sync_readahead(struct address_space *mapping,
 	}
 
 	/* do read-ahead */
-	ondemand_readahead(mapping, ra, filp, false, index, req_count);
+	ondemand_readahead(&ractl, ra, false, req_count);
 }
 EXPORT_SYMBOL_GPL(page_cache_sync_readahead);
 
@@ -602,6 +605,8 @@ page_cache_async_readahead(struct address_space *mapping,
 			   struct page *page, pgoff_t index,
 			   unsigned long req_count)
 {
+	DEFINE_READAHEAD(ractl, filp, mapping, index);
+
 	/* no read-ahead */
 	if (!ra->ra_pages)
 		return;
@@ -624,7 +629,7 @@ page_cache_async_readahead(struct address_space *mapping,
 		return;
 
 	/* do read-ahead */
-	ondemand_readahead(mapping, ra, filp, true, index, req_count);
+	ondemand_readahead(&ractl, ra, true, req_count);
 }
 EXPORT_SYMBOL_GPL(page_cache_async_readahead);