On 8/15/24 15:33, Jens Axboe wrote:
On 8/14/24 7:42 PM, Ming Lei wrote:
On Wed, Aug 14, 2024 at 6:46?PM Pavel Begunkov <asml.silence@xxxxxxxxx> wrote:
Add ->uring_cmd callback for block device files and use it to implement
asynchronous discard. Normally, it first tries to execute the command
from non-blocking context, which we limit to a single bio because
otherwise one of sub-bios may need to wait for other bios, and we don't
want to deal with partial IO. If non-blocking attempt fails, we'll retry
it in a blocking context.
Suggested-by: Conrad Meyer <conradmeyer@xxxxxxxx>
Signed-off-by: Pavel Begunkov <asml.silence@xxxxxxxxx>
---
block/blk.h | 1 +
block/fops.c | 2 +
block/ioctl.c | 94 +++++++++++++++++++++++++++++++++++++++++
include/uapi/linux/fs.h | 2 +
4 files changed, 99 insertions(+)
diff --git a/block/blk.h b/block/blk.h
index e180863f918b..5178c5ba6852 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -571,6 +571,7 @@ blk_mode_t file_to_blk_mode(struct file *file);
int truncate_bdev_range(struct block_device *bdev, blk_mode_t mode,
loff_t lstart, loff_t lend);
long blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg);
+int blkdev_uring_cmd(struct io_uring_cmd *cmd, unsigned int issue_flags);
long compat_blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg);
extern const struct address_space_operations def_blk_aops;
diff --git a/block/fops.c b/block/fops.c
index 9825c1713a49..8154b10b5abf 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -17,6 +17,7 @@
#include <linux/fs.h>
#include <linux/iomap.h>
#include <linux/module.h>
+#include <linux/io_uring/cmd.h>
#include "blk.h"
static inline struct inode *bdev_file_inode(struct file *file)
@@ -873,6 +874,7 @@ const struct file_operations def_blk_fops = {
.splice_read = filemap_splice_read,
.splice_write = iter_file_splice_write,
.fallocate = blkdev_fallocate,
+ .uring_cmd = blkdev_uring_cmd,
Just be curious, we have IORING_OP_FALLOCATE already for sending
discard to block device, why is .uring_cmd added for this purpose?
Which is a good question, I haven't thought about it, but I tend to
agree with Jens. Because vfs_fallocate is created synchronous
IORING_OP_FALLOCATE is slow for anything but pretty large requests.
Probably can be patched up, which would involve changing the
fops->fallocate protot, but I'm not sure async there makes sense
outside of bdev (?), and cmd approach is simpler, can be made
somewhat more efficient (1 less layer in the way), and it's not
really something completely new since we have it in ioctl.
I think wiring up a bdev uring_cmd makes sense, because:
1) The existing FALLOCATE op is using vfs_fallocate, which is inherently
sync and hence always punted to io-wq.
2) There will most certainly be other async ops that would be
interesting to add, at which point we'd need it anyway.
3) It arguably makes more sense to have a direct discard op than use
fallocate for this, if working on a raw bdev.
And probably others...
--
Pavel Begunkov
