btrfs: rename page_size to io_size in submit_extent_page

The variable @page_size in submit_extent_page() is not related to page
size.

It can already be smaller than PAGE_SIZE, so rename it to io_size to
reduce confusion, this is especially important for later subpage
support.
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -3044,7 +3044,7 @@ static int submit_extent_page(unsigned int opf,
 {
 	int ret = 0;
 	struct bio *bio;
-	size_t page_size = min_t(size_t, size, PAGE_SIZE);
+	size_t io_size = min_t(size_t, size, PAGE_SIZE);
 	sector_t sector = offset >> 9;
 	struct extent_io_tree *tree = &BTRFS_I(page->mapping->host)->io_tree;
 
@@ -3060,12 +3060,12 @@ static int submit_extent_page(unsigned int opf,
 		else
 			contig = bio_end_sector(bio) == sector;
 
-		if (btrfs_bio_fits_in_stripe(page, page_size, bio, bio_flags))
+		if (btrfs_bio_fits_in_stripe(page, io_size, bio, bio_flags))
 			can_merge = false;
 
 		if (prev_bio_flags != bio_flags || !contig || !can_merge ||
 		    force_bio_submit ||
-		    bio_add_page(bio, page, page_size, pg_offset) < page_size) {
+		    bio_add_page(bio, page, io_size, pg_offset) < io_size) {
 			ret = submit_one_bio(bio, mirror_num, prev_bio_flags);
 			if (ret < 0) {
 				*bio_ret = NULL;
@@ -3074,13 +3074,13 @@ static int submit_extent_page(unsigned int opf,
 			bio = NULL;
 		} else {
 			if (wbc)
-				wbc_account_cgroup_owner(wbc, page, page_size);
+				wbc_account_cgroup_owner(wbc, page, io_size);
 			return 0;
 		}
 	}
 
 	bio = btrfs_bio_alloc(offset);
-	bio_add_page(bio, page, page_size, pg_offset);
+	bio_add_page(bio, page, io_size, pg_offset);
 	bio->bi_end_io = end_io_func;
 	bio->bi_private = tree;
 	bio->bi_write_hint = page->mapping->host->i_write_hint;
@@ -3091,7 +3091,7 @@ static int submit_extent_page(unsigned int opf,
 		bdev = BTRFS_I(page->mapping->host)->root->fs_info->fs_devices->latest_bdev;
 		bio_set_dev(bio, bdev);
 		wbc_init_bio(wbc, bio);
-		wbc_account_cgroup_owner(wbc, page, page_size);
+		wbc_account_cgroup_owner(wbc, page, io_size);
 	}
 
 	*bio_ret = bio;