Hi Christoph,
On Tue, Aug 01, 2023 at 07:22:00PM +0200, Christoph Hellwig wrote:
> Use iomap in buffer_head compat mode to write to block devices.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> Reviewed-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> Reviewed-by: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
> Reviewed-by: Hannes Reinecke <hare@xxxxxxx>
> ---
> block/Kconfig | 1 +
> block/fops.c | 31 +++++++++++++++++++++++++++++--
> 2 files changed, 30 insertions(+), 2 deletions(-)
>
> diff --git a/block/Kconfig b/block/Kconfig
> index 86122e459fe046..1a13ef0b1ca10c 100644
> --- a/block/Kconfig
> +++ b/block/Kconfig
> @@ -5,6 +5,7 @@
> menuconfig BLOCK
> bool "Enable the block layer" if EXPERT
> default y
> + select FS_IOMAP
> select SBITMAP
> help
> Provide block layer support for the kernel.
> diff --git a/block/fops.c b/block/fops.c
> index f0b822c28ddfe2..063ece37d44e44 100644
> --- a/block/fops.c
> +++ b/block/fops.c
> @@ -15,6 +15,7 @@
> #include <linux/falloc.h>
> #include <linux/suspend.h>
> #include <linux/fs.h>
> +#include <linux/iomap.h>
> #include <linux/module.h>
> #include "blk.h"
>
> @@ -386,6 +387,27 @@ static ssize_t blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
> return __blkdev_direct_IO(iocb, iter, bio_max_segs(nr_pages));
> }
>
> +static int blkdev_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> + unsigned int flags, struct iomap *iomap, struct iomap *srcmap)
> +{
> + struct block_device *bdev = I_BDEV(inode);
> + loff_t isize = i_size_read(inode);
> +
> + iomap->bdev = bdev;
> + iomap->offset = ALIGN_DOWN(offset, bdev_logical_block_size(bdev));
> + if (iomap->offset >= isize)
> + return -EIO;
> + iomap->type = IOMAP_MAPPED;
> + iomap->addr = iomap->offset;
> + iomap->length = isize - iomap->offset;
> + iomap->flags |= IOMAP_F_BUFFER_HEAD;
> + return 0;
> +}
> +
> +static const struct iomap_ops blkdev_iomap_ops = {
> + .iomap_begin = blkdev_iomap_begin,
> +};
> +
> static int blkdev_writepage(struct page *page, struct writeback_control *wbc)
> {
> return block_write_full_page(page, blkdev_get_block, wbc);
> @@ -556,6 +578,11 @@ blkdev_direct_write(struct kiocb *iocb, struct iov_iter *from)
> return written;
> }
>
> +static ssize_t blkdev_buffered_write(struct kiocb *iocb, struct iov_iter *from)
> +{
> + return iomap_file_buffered_write(iocb, from, &blkdev_iomap_ops);
> +}
> +
> /*
> * Write data to the block device. Only intended for the block device itself
> * and the raw driver which basically is a fake block device.
> @@ -605,9 +632,9 @@ static ssize_t blkdev_write_iter(struct kiocb *iocb, struct iov_iter *from)
> ret = blkdev_direct_write(iocb, from);
> if (ret >= 0 && iov_iter_count(from))
> ret = direct_write_fallback(iocb, from, ret,
> - generic_perform_write(iocb, from));
> + blkdev_buffered_write(iocb, from));
> } else {
> - ret = generic_perform_write(iocb, from);
> + ret = blkdev_buffered_write(iocb, from);
> }
>
> if (ret > 0)
I'm testing SSD block device write performance recently. I found the write
speed descrased greatly on my board (330MB/s -> 130MB/s). Then I spent some
time to find cause, finally find that it's caused by this patch and if I
revert this patch, write speed can recover to 330MB/s.
I'm using below command to test write performance:
dd if=/dev/zero of=/dev/sda bs=4M count=1024
And I also do more tests to get more findings. In short, I found write
speed changes with the "bs=" parameter.
I totally write 4GB data to sda for each test, the results as below:
- dd if=/dev/zero of=/dev/sda bs=400K count=10485 (334 MB/s)
- dd if=/dev/zero of=/dev/sda bs=800K count=5242 (278 MB/s)
- dd if=/dev/zero of=/dev/sda bs=1600K count=2621 (204 MB/s)
- dd if=/dev/zero of=/dev/sda bs=2200K count=1906 (170 MB/s)
- dd if=/dev/zero of=/dev/sda bs=3000K count=1398 (150 MB/s)
- dd if=/dev/zero of=/dev/sda bs=4500K count=932 (139 MB/s)
When this patch reverted, I got below results:
- dd if=/dev/zero of=/dev/sda bs=400K count=10485 (339 MB/s)
- dd if=/dev/zero of=/dev/sda bs=800K count=5242 (330 MB/s)
- dd if=/dev/zero of=/dev/sda bs=1600K count=2621 (332 MB/s)
- dd if=/dev/zero of=/dev/sda bs=2200K count=1906 (333 MB/s)
- dd if=/dev/zero of=/dev/sda bs=3000K count=1398 (333 MB/s)
- dd if=/dev/zero of=/dev/sda bs=4500K count=932 (333 MB/s)
I just want to know if this results is expected when uses iomap, or it's
a real issue?
Many thanks in advance!
Best Regards,
Xu Yang
> --
> 2.39.2
>
