mpage: add argument structure for do_mpage_readpage()

Patch series "Submit ->readpages() IO as read-ahead", v4.

The only caller of ->readpages() is from read-ahead, yet we don't submit
IO flagged with REQ_RAHEAD.  This means we don't see it in blktrace, for
instance, which is a shame.  Additionally, it's preventing further
functional changes in the block layer for deadling with read-ahead more
intelligently.  We already make assumptions about ->readpages() just
being for read-ahead in the mpage implementation, using
readahead_gfp_mask(mapping) as out GFP mask of choice.

This small series fixes up mpage_readpages() to submit with REQ_RAHEAD,
which takes care of file systems using mpage_readpages().  The first
patch is a prep patch, that makes do_mpage_readpage() take an argument
structure.

This patch (of 4):

We're currently passing 8 arguments to this function, clean it up a bit
by packing the arguments in an args structure we pass to it.

No intentional functional changes in this patch.

[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/20180621010725.17813-2-axboe@kernel.dkSigned-off-by: NJens Axboe <axboe@kernel.dk>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Chris Mason <clm@fb.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/mpage.c

@@ -133,6 +133,17 @@ map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
 	} while (page_bh != head);
 }
 
+struct mpage_readpage_args {
+	struct bio *bio;
+	struct page *page;
+	unsigned int nr_pages;
+	sector_t last_block_in_bio;
+	struct buffer_head map_bh;
+	unsigned long first_logical_block;
+	get_block_t *get_block;
+	gfp_t gfp;
+};
+
 /*
  * This is the worker routine which does all the work of mapping the disk
  * blocks and constructs largest possible bios, submits them for IO if the
@@ -142,16 +153,14 @@ map_buffer_to_page(struct page *page, struct buffer_head *bh, int page_block)
  * represent the validity of its disk mapping and to decide when to do the next
  * get_block() call.
  */
-static struct bio *
-do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
-		sector_t *last_block_in_bio, struct buffer_head *map_bh,
-		unsigned long *first_logical_block, get_block_t get_block,
-		gfp_t gfp)
+static struct bio *do_mpage_readpage(struct mpage_readpage_args *args)
 {
+	struct page *page = args->page;
 	struct inode *inode = page->mapping->host;
 	const unsigned blkbits = inode->i_blkbits;
 	const unsigned blocks_per_page = PAGE_SIZE >> blkbits;
 	const unsigned blocksize = 1 << blkbits;
+	struct buffer_head *map_bh = &args->map_bh;
 	sector_t block_in_file;
 	sector_t last_block;
 	sector_t last_block_in_file;
@@ -168,7 +177,7 @@ do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
 		goto confused;
 
 	block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
-	last_block = block_in_file + nr_pages * blocks_per_page;
+	last_block = block_in_file + args->nr_pages * blocks_per_page;
 	last_block_in_file = (i_size_read(inode) + blocksize - 1) >> blkbits;
 	if (last_block > last_block_in_file)
 		last_block = last_block_in_file;
@@ -178,9 +187,10 @@ do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
 	 * Map blocks using the result from the previous get_blocks call first.
 	 */
 	nblocks = map_bh->b_size >> blkbits;
-	if (buffer_mapped(map_bh) && block_in_file > *first_logical_block &&
-			block_in_file < (*first_logical_block + nblocks)) {
-		unsigned map_offset = block_in_file - *first_logical_block;
+	if (buffer_mapped(map_bh) &&
+			block_in_file > args->first_logical_block &&
+			block_in_file < (args->first_logical_block + nblocks)) {
+		unsigned map_offset = block_in_file - args->first_logical_block;
 		unsigned last = nblocks - map_offset;
 
 		for (relative_block = 0; ; relative_block++) {
@@ -208,9 +218,9 @@ do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
 
 		if (block_in_file < last_block) {
 			map_bh->b_size = (last_block-block_in_file) << blkbits;
-			if (get_block(inode, block_in_file, map_bh, 0))
+			if (args->get_block(inode, block_in_file, map_bh, 0))
 				goto confused;
-			*first_logical_block = block_in_file;
+			args->first_logical_block = block_in_file;
 		}
 
 		if (!buffer_mapped(map_bh)) {
@@ -273,43 +283,45 @@ do_mpage_readpage(struct bio *bio, struct page *page, unsigned nr_pages,
 	/*
 	 * This page will go to BIO.  Do we need to send this BIO off first?
 	 */
-	if (bio && (*last_block_in_bio != blocks[0] - 1))
-		bio = mpage_bio_submit(REQ_OP_READ, 0, bio);
+	if (args->bio && (args->last_block_in_bio != blocks[0] - 1))
+		args->bio = mpage_bio_submit(REQ_OP_READ, 0, args->bio);
 
 alloc_new:
-	if (bio == NULL) {
+	if (args->bio == NULL) {
 		if (first_hole == blocks_per_page) {
 			if (!bdev_read_page(bdev, blocks[0] << (blkbits - 9),
 								page))
 				goto out;
 		}
-		bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
-				min_t(int, nr_pages, BIO_MAX_PAGES), gfp);
-		if (bio == NULL)
+		args->bio = mpage_alloc(bdev, blocks[0] << (blkbits - 9),
+					min_t(int, args->nr_pages,
+					      BIO_MAX_PAGES),
+					args->gfp);
+		if (args->bio == NULL)
 			goto confused;
 	}
 
 	length = first_hole << blkbits;
-	if (bio_add_page(bio, page, length, 0) < length) {
-		bio = mpage_bio_submit(REQ_OP_READ, 0, bio);
+	if (bio_add_page(args->bio, page, length, 0) < length) {
+		args->bio = mpage_bio_submit(REQ_OP_READ, 0, args->bio);
 		goto alloc_new;
 	}
 
-	relative_block = block_in_file - *first_logical_block;
+	relative_block = block_in_file - args->first_logical_block;
 	nblocks = map_bh->b_size >> blkbits;
 	if ((buffer_boundary(map_bh) && relative_block == nblocks) ||
 	    (first_hole != blocks_per_page))
-		bio = mpage_bio_submit(REQ_OP_READ, 0, bio);
+		args->bio = mpage_bio_submit(REQ_OP_READ, 0, args->bio);
 	else
-		*last_block_in_bio = blocks[blocks_per_page - 1];
+		args->last_block_in_bio = blocks[blocks_per_page - 1];
 out:
-	return bio;
+	return args->bio;
 
 confused:
-	if (bio)
-		bio = mpage_bio_submit(REQ_OP_READ, 0, bio);
+	if (args->bio)
+		args->bio = mpage_bio_submit(REQ_OP_READ, 0, args->bio);
 	if (!PageUptodate(page))
-	        block_read_full_page(page, get_block);
+		block_read_full_page(page, args->get_block);
 	else
 		unlock_page(page);
 	goto out;
@@ -363,15 +375,12 @@ int
 mpage_readpages(struct address_space *mapping, struct list_head *pages,
 				unsigned nr_pages, get_block_t get_block)
 {
-	struct bio *bio = NULL;
+	struct mpage_readpage_args args = {
+		.get_block = get_block,
+		.gfp = readahead_gfp_mask(mapping),
+	};
 	unsigned page_idx;
-	sector_t last_block_in_bio = 0;
-	struct buffer_head map_bh;
-	unsigned long first_logical_block = 0;
-	gfp_t gfp = readahead_gfp_mask(mapping);
 
-	map_bh.b_state = 0;
-	map_bh.b_size = 0;
 	for (page_idx = 0; page_idx < nr_pages; page_idx++) {
 		struct page *page = lru_to_page(pages);
 
@@ -379,18 +388,16 @@ mpage_readpages(struct address_space *mapping, struct list_head *pages,
 		list_del(&page->lru);
 		if (!add_to_page_cache_lru(page, mapping,
 					page->index,
-					gfp)) {
-			bio = do_mpage_readpage(bio, page,
-					nr_pages - page_idx,
-					&last_block_in_bio, &map_bh,
-					&first_logical_block,
-					get_block, gfp);
+					args.gfp)) {
+			args.page = page;
+			args.nr_pages = nr_pages - page_idx;
+			args.bio = do_mpage_readpage(&args);
 		}
 		put_page(page);
 	}
 	BUG_ON(!list_empty(pages));
-	if (bio)
-		mpage_bio_submit(REQ_OP_READ, 0, bio);
+	if (args.bio)
+		mpage_bio_submit(REQ_OP_READ, 0, args.bio);
 	return 0;
 }
 EXPORT_SYMBOL(mpage_readpages);
@@ -400,18 +407,16 @@ EXPORT_SYMBOL(mpage_readpages);
  */
 int mpage_readpage(struct page *page, get_block_t get_block)
 {
-	struct bio *bio = NULL;
-	sector_t last_block_in_bio = 0;
-	struct buffer_head map_bh;
-	unsigned long first_logical_block = 0;
-	gfp_t gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL);
+	struct mpage_readpage_args args = {
+		.page = page,
+		.nr_pages = 1,
+		.get_block = get_block,
+		.gfp = mapping_gfp_constraint(page->mapping, GFP_KERNEL),
+	};
 
-	map_bh.b_state = 0;
-	map_bh.b_size = 0;
-	bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
-			&map_bh, &first_logical_block, get_block, gfp);
-	if (bio)
-		mpage_bio_submit(REQ_OP_READ, 0, bio);
+	args.bio = do_mpage_readpage(&args);
+	if (args.bio)
+		mpage_bio_submit(REQ_OP_READ, 0, args.bio);
 	return 0;
 }
 EXPORT_SYMBOL(mpage_readpage);