The patch titled
Subject: block_dev: implement readpages() to optimize sequential read
has been added to the -mm tree. Its filename is
block_dev-implement-readpages-to-optimize-sequential-read.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/block_dev-implement-readpages-to-optimize-sequential-read.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/block_dev-implement-readpages-to-optimize-sequential-read.patch
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------------------------------------------------------
From: Akinobu Mita <akinobu.mita@xxxxxxxxx>
Subject: 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: Akinobu Mita <akinobu.mita@xxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Jeff Moyer <jmoyer@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/block_dev.c | 7 +++++++
1 file changed, 7 insertions(+)
diff -puN fs/block_dev.c~block_dev-implement-readpages-to-optimize-sequential-read fs/block_dev.c
--- a/fs/block_dev.c~block_dev-implement-readpages-to-optimize-sequential-read
+++ a/fs/block_dev.c
@@ -304,6 +304,12 @@ static int blkdev_readpage(struct file *
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 pag
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,
_
Patches currently in -mm which might be from akinobu.mita@xxxxxxxxx are
vfs-make-guard_bh_eod-more-generic.patch
vfs-guard-end-of-device-for-mpage-interface.patch
block_dev-implement-readpages-to-optimize-sequential-read.patch
linux-next.patch
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