block: remove ->rw_page

The ->rw_page method is a special purpose bypass of the usual bio handling
path that is limited to single-page reads and writes and synchronous which
causes a lot of extra code in the drivers, callers and the block layer.

The only remaining user is the MM swap code.  Switch that swap code to
simply submit a single-vec on-stack bio an synchronously wait on it based
on a newly added QUEUE_FLAG_SYNCHRONOUS flag set by the drivers that
currently implement ->rw_page instead.  While this touches one extra cache
line and executes extra code, it simplifies the block layer and drivers
and ensures that all feastures are properly supported by all drivers, e.g.
right now ->rw_page bypassed cgroup writeback entirely.

[akpm@linux-foundation.org: fix comment typo, per Dan]
Link: https://lkml.kernel.org/r/20230125133436.447864-8-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Keith Busch <kbusch@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 1 insertions, 14 deletions

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 20acc4a1fd6d..37dce184eb56 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -309,23 +309,9 @@ static void brd_submit_bio(struct bio *bio)
 	bio_endio(bio);
 }
 
-static int brd_rw_page(struct block_device *bdev, sector_t sector,
-		       struct page *page, enum req_op op)
-{
-	struct brd_device *brd = bdev->bd_disk->private_data;
-	int err;
-
-	if (PageTransHuge(page))
-		return -ENOTSUPP;
-	err = brd_do_bvec(brd, page, PAGE_SIZE, 0, op, sector);
-	page_endio(page, op_is_write(op), err);
-	return err;
-}
-
 static const struct block_device_operations brd_fops = {
 	.owner =		THIS_MODULE,
 	.submit_bio =		brd_submit_bio,
-	.rw_page =		brd_rw_page,
 };
 
 /*
@@ -411,6 +397,7 @@ static int brd_alloc(int i)
 
 	/* Tell the block layer that this is not a rotational device */
 	blk_queue_flag_set(QUEUE_FLAG_NONROT, disk->queue);
+	blk_queue_flag_set(QUEUE_FLAG_SYNCHRONOUS, disk->queue);
 	blk_queue_flag_clear(QUEUE_FLAG_ADD_RANDOM, disk->queue);
 	err = add_disk(disk);
 	if (err)