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From: Ming Lei <[email protected]>
To: Jens Axboe <[email protected]>
Cc: Pavel Begunkov <[email protected]>,
	[email protected], Conrad Meyer <[email protected]>,
	[email protected], [email protected],
	[email protected]
Subject: Re: [RFC 5/5] block: implement io_uring discard cmd
Date: Fri, 16 Aug 2024 09:45:06 +0800	[thread overview]
Message-ID: <Zr6vIt1uSe9/xguH@fedora> (raw)
In-Reply-To: <[email protected]>

On Thu, Aug 15, 2024 at 07:24:16PM -0600, Jens Axboe wrote:
> On 8/15/24 5:44 PM, Ming Lei wrote:
> > On Thu, Aug 15, 2024 at 06:11:13PM +0100, Pavel Begunkov wrote:
> >> 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 <[email protected]> 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 <[email protected]>
> >>>>> Signed-off-by: Pavel Begunkov <[email protected]>
> >>>>> ---
> >>>>>   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.
> > 
> > Yeah, we have ioctl(DISCARD), which acquires filemap_invalidate_lock,
> > same with blkdev_fallocate().
> > 
> > But this patch drops this exclusive lock, so it becomes async friendly,
> > but may cause stale page cache. However, if the lock is required, it can't
> > be efficient anymore and io-wq may be inevitable, :-)
> 
> If you want to grab the lock, you can still opportunistically grab it.
> For (by far) the common case, you'll get it, and you can still do it
> inline.

If the lock is grabbed in the whole cmd lifetime, it is basically one sync
interface cause there is at most one async discard cmd in-flight for each
device.

Meantime the handling has to move to io-wq for avoiding to block current
context, the interface becomes same with IORING_OP_FALLOCATE?


thanks,
Ming


  reply	other threads:[~2024-08-16  1:45 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-08-14 10:45 [RFC 0/5] implement asynchronous BLKDISCARD via io_uring Pavel Begunkov
2024-08-14 10:45 ` [RFC 1/5] io_uring/cmd: expose iowq to cmds Pavel Begunkov
2024-08-14 10:45 ` [RFC 2/5] io_uring/cmd: give inline space in request " Pavel Begunkov
2024-08-14 10:45 ` [RFC 3/5] filemap: introduce filemap_invalidate_pages Pavel Begunkov
2024-08-14 10:45 ` [RFC 4/5] block: introduce blk_validate_discard() Pavel Begunkov
2024-08-14 10:45 ` [RFC 5/5] block: implement io_uring discard cmd Pavel Begunkov
2024-08-15  1:42   ` Ming Lei
2024-08-15 14:33     ` Jens Axboe
2024-08-15 17:11       ` Pavel Begunkov
2024-08-15 23:44         ` Ming Lei
2024-08-16  1:24           ` Jens Axboe
2024-08-16  1:45             ` Ming Lei [this message]
2024-08-16  1:59               ` Pavel Begunkov
2024-08-16  2:08                 ` Ming Lei
2024-08-16  2:16                   ` Pavel Begunkov
2024-08-19 20:02                     ` Jens Axboe
2024-08-19 20:01               ` Jens Axboe
2024-08-20  2:36                 ` Ming Lei
2024-08-20 16:30                   ` Jens Axboe
2024-08-20 17:19                     ` Pavel Begunkov
2024-08-21  2:55                       ` Ming Lei
2024-08-15 14:42   ` Jens Axboe
2024-08-15 15:50 ` [RFC 0/5] implement asynchronous BLKDISCARD via io_uring Jens Axboe
2024-08-15 17:26   ` Pavel Begunkov
2024-08-15 16:15 ` Martin K. Petersen
2024-08-15 17:12   ` Pavel Begunkov

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