Commit 447f05bb authored by Akinobu Mita's avatar Akinobu Mita Committed by Linus Torvalds

block_dev: implement readpages() to optimize sequential read

Sequential read from a block device is expected to be equal or faster than
from the file on a filesystem.  But it is not correct due to the lack of
effective readpages() in the address space operations for block device.

This implements readpages() operation for block device by using
mpage_readpages() which can create multipage BIOs instead of BIOs for each
page and reduce system CPU time consumption.

Install 1GB of RAM disk storage:

	# modprobe scsi_debug dev_size_mb=1024 delay=0

Sequential read from file on a filesystem:

	# mkfs.ext4 /dev/$DEV
	# mount /dev/$DEV /mnt
	# fio --name=t --size=512m --rw=read --filename=/mnt/file
	...
	  read : io=524288KB, bw=2133.4MB/s, iops=546133, runt=   240msec

Sequential read from a block device:
	# fio --name=t --size=512m --rw=read --filename=/dev/$DEV
	...
(Without this commit)
	  read : io=524288KB, bw=1700.2MB/s, iops=435455, runt=   301msec

(With this commit)
	  read : io=524288KB, bw=2160.4MB/s, iops=553046, runt=   237msec
Signed-off-by: default avatarAkinobu Mita <[email protected]>
Cc: Jens Axboe <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Jeff Moyer <[email protected]>
Signed-off-by: default avatarAndrew Morton <[email protected]>
Signed-off-by: default avatarLinus Torvalds <[email protected]>
parent 4db96b71
......@@ -304,6 +304,12 @@ static int blkdev_readpage(struct file * file, struct page * page)
return block_read_full_page(page, blkdev_get_block);
}
static int blkdev_readpages(struct file *file, struct address_space *mapping,
struct list_head *pages, unsigned nr_pages)
{
return mpage_readpages(mapping, pages, nr_pages, blkdev_get_block);
}
static int blkdev_write_begin(struct file *file, struct address_space *mapping,
loff_t pos, unsigned len, unsigned flags,
struct page **pagep, void **fsdata)
......@@ -1622,6 +1628,7 @@ static int blkdev_releasepage(struct page *page, gfp_t wait)
static const struct address_space_operations def_blk_aops = {
.readpage = blkdev_readpage,
.readpages = blkdev_readpages,
.writepage = blkdev_writepage,
.write_begin = blkdev_write_begin,
.write_end = blkdev_write_end,
......
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