ext4: make ext4_bio_write_page() use BH_Async_Write flags

So far ext4_bio_write_page() attached all the pages to ext4_io_end
structure.  This makes that structure pretty heavy (1 KB for pointers
+ 16 bytes per page attached to the bio).  Also later we would like to
share ext4_io_end structure among several bios in case IO to a single
extent needs to be split among several bios and pointing to pages from
ext4_io_end makes this complex.

We remove page pointers from ext4_io_end and use pointers from bio
itself instead.  This isn't as easy when blocksize < pagesize because
then we can have several bios in flight for a single page and we have
to be careful when to call end_page_writeback().  However this is a
known problem already solved by block_write_full_page() /
end_buffer_async_write() so we mimic its behavior here.  We mark
buffers going to disk with BH_Async_Write flag and in
ext4_bio_end_io() we check whether there are any buffers with
BH_Async_Write flag left.  If there are not, we can call
end_page_writeback().

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Dmitry Monakhov <dmonakhov@openvz.org>
Reviewed-by: Zheng Liu <wenqing.lz@taobao.com>

1 files changed, 0 insertions, 14 deletions

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 75b2326b04c..3b41d4ae6f9 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -198,19 +198,8 @@ struct mpage_da_data {
 #define EXT4_IO_END_ERROR	0x0002
 #define EXT4_IO_END_DIRECT	0x0004
 
-struct ext4_io_page {
-	struct page	*p_page;
-	atomic_t	p_count;
-};
-
-#define MAX_IO_PAGES 128
-
 /*
  * For converting uninitialized extents on a work queue.
- *
- * 'page' is only used from the writepage() path; 'pages' is only used for
- * buffered writes; they are used to keep page references until conversion
- * takes place.  For AIO/DIO, neither field is filled in.
  */
 typedef struct ext4_io_end {
 	struct list_head	list;		/* per-file finished IO list */
@@ -220,15 +209,12 @@ typedef struct ext4_io_end {
 	ssize_t			size;		/* size of the extent */
 	struct kiocb		*iocb;		/* iocb struct for AIO */
 	int			result;		/* error value for AIO */
-	int			num_io_pages;   /* for writepages() */
-	struct ext4_io_page	*pages[MAX_IO_PAGES]; /* for writepages() */
 } ext4_io_end_t;
 
 struct ext4_io_submit {
 	int			io_op;
 	struct bio		*io_bio;
 	ext4_io_end_t		*io_end;
-	struct ext4_io_page	*io_page;
 	sector_t		io_next_block;
 };