Messages in this thread Patch in this message | | | From | Akinobu Mita <> | Subject | [PATCH] block_dev: implement readpages() to optimize sequential read | Date | Thu, 17 Jul 2014 23:17:39 +0900 |
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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. It enables to 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/sdb ... (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@gmail.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Jens Axboe <axboe@kernel.dk> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org --- fs/block_dev.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/fs/block_dev.c b/fs/block_dev.c index 6d72746..e2f3ad08 100644 --- a/fs/block_dev.c +++ b/fs/block_dev.c @@ -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, -- 1.9.1
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