mm/readahead: make do_page_cache_ra take a readahead_control

Rename __do_page_cache_readahead() to do_page_cache_ra() and call it
directly from ondemand_readahead() instead of indirecting via ra_submit().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: David Howells <dhowells@redhat.com>
Cc: Eric Biggers <ebiggers@google.com>
Link: https://lkml.kernel.org/r/20200903140844.14194-5-willy@infradead.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Author: Matthew Wilcox (Oracle)

mm/internal.h

@@ -51,18 +51,17 @@ void unmap_page_range(struct mmu_gather *tlb,
 
 void force_page_cache_readahead(struct address_space *, struct file *,
 		pgoff_t index, unsigned long nr_to_read);
-void __do_page_cache_readahead(struct address_space *, struct file *,
-		pgoff_t index, unsigned long nr_to_read,
-		unsigned long lookahead_size);
+void do_page_cache_ra(struct readahead_control *,
+		unsigned long nr_to_read, unsigned long lookahead_size);
 
 /*
  * Submit IO for the read-ahead request in file_ra_state.
  */
 static inline void ra_submit(struct file_ra_state *ra,
-		struct address_space *mapping, struct file *filp)
+		struct address_space *mapping, struct file *file)
 {
-	__do_page_cache_readahead(mapping, filp,
-			ra->start, ra->size, ra->async_size);
+	DEFINE_READAHEAD(ractl, file, mapping, ra->start);
+	do_page_cache_ra(&ractl, ra->size, ra->async_size);
 }
 
 struct page *find_get_entry(struct address_space *mapping, pgoff_t index);

mm/readahead.c

@@ -241,17 +241,16 @@ void page_cache_ra_unbounded(struct readahead_control *ractl,
 EXPORT_SYMBOL_GPL(page_cache_ra_unbounded);
 
 /*
- * __do_page_cache_readahead() actually reads a chunk of disk.  It allocates
+ * do_page_cache_ra() 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.
  */
-void __do_page_cache_readahead(struct address_space *mapping,
-		struct file *file, pgoff_t index, unsigned long nr_to_read,
-		unsigned long lookahead_size)
+void do_page_cache_ra(struct readahead_control *ractl,
+		unsigned long nr_to_read, unsigned long lookahead_size)
 {
-	DEFINE_READAHEAD(ractl, file, mapping, index);
-	struct inode *inode = mapping->host;
+	struct inode *inode = ractl->mapping->host;
+	unsigned long index = readahead_index(ractl);
 	loff_t isize = i_size_read(inode);
 	pgoff_t end_index;	/* The last page we want to read */
 
@@ -265,18 +264,19 @@ void __do_page_cache_readahead(struct address_space *mapping,
 	if (nr_to_read > end_index - index)
 		nr_to_read = end_index - index + 1;
 
-	page_cache_ra_unbounded(&ractl, nr_to_read, lookahead_size);
+	page_cache_ra_unbounded(ractl, nr_to_read, lookahead_size);
 }
 
 /*
  * Chunk the readahead into 2 megabyte units, so that we don't pin too much
  * memory at once.
  */
 void force_page_cache_readahead(struct address_space *mapping,
-		struct file *filp, pgoff_t index, unsigned long nr_to_read)
+		struct file *file, pgoff_t index, unsigned long nr_to_read)
 {
+	DEFINE_READAHEAD(ractl, file, mapping, index);
 	struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
-	struct file_ra_state *ra = &filp->f_ra;
+	struct file_ra_state *ra = &file->f_ra;
 	unsigned long max_pages;
 
 	if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages &&
@@ -294,7 +294,7 @@ void force_page_cache_readahead(struct address_space *mapping,
 
 		if (this_chunk > nr_to_read)
 			this_chunk = nr_to_read;
-		__do_page_cache_readahead(mapping, filp, index, this_chunk, 0);
+		do_page_cache_ra(&ractl, this_chunk, 0);
 
 		index += this_chunk;
 		nr_to_read -= this_chunk;
@@ -432,10 +432,11 @@ 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 *filp,
+		struct file_ra_state *ra, struct file *file,
 		bool hit_readahead_marker, pgoff_t index,
 		unsigned long req_size)
 {
+	DEFINE_READAHEAD(ractl, file, mapping, index);
 	struct backing_dev_info *bdi = inode_to_bdi(mapping->host);
 	unsigned long max_pages = ra->ra_pages;
 	unsigned long add_pages;
@@ -516,7 +517,7 @@ static void ondemand_readahead(struct address_space *mapping,
 	 * standalone, small random read
 	 * Read as is, and do not pollute the readahead state.
 	 */
-	__do_page_cache_readahead(mapping, filp, index, req_size, 0);
+	do_page_cache_ra(&ractl, req_size, 0);
 	return;
 
 initial_readahead:
@@ -542,7 +543,8 @@ static void ondemand_readahead(struct address_space *mapping,
 		}
 	}
 
-	ra_submit(ra, mapping, filp);
+	ractl._index = ra->start;
+	do_page_cache_ra(&ractl, ra->size, ra->async_size);
 }
 
 /**