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From: Ming Lei <[email protected]>
To: Pavel Machek <[email protected]>
Cc: Jens Axboe <[email protected]>,
	[email protected], [email protected],
	[email protected],
	Gabriel Krisman Bertazi <[email protected]>,
	ZiyangZhang <[email protected]>,
	Xiaoguang Wang <[email protected]>
Subject: Re: [RFC PATCH] ubd: add io_uring based userspace block driver
Date: Thu, 2 Jun 2022 11:19:42 +0800	[thread overview]
Message-ID: <YpgsTojc4mVKghZA@T590> (raw)
In-Reply-To: <20220530070700.GF1363@bug>

Hello Pavel,

On Mon, May 30, 2022 at 09:07:00AM +0200, Pavel Machek wrote:
> Hi!
> 
> > This is the driver part of userspace block driver(ubd driver), the other
> > part is userspace daemon part(ubdsrv)[1].
> 
> > @@ -0,0 +1,1193 @@
> > +// SPDX-License-Identifier: GPL-2.0-or-later
> > +/*
> > + * Userspace block device - block device which IO is handled from userspace
> > + *
> > + * Take full use of io_uring passthrough command for communicating with
> > + * ubd userspace daemon(ubdsrvd) for handling basic IO request.
> 
> > +
> > +static inline unsigned int ubd_req_build_flags(struct request *req)
> > +{
> ...
> > +	if (req->cmd_flags & REQ_SWAP)
> > +		flags |= UBD_IO_F_SWAP;
> > +
> > +	return flags;
> > +}
> 
> Does it work? How do you guarantee operation will be deadlock-free with swapping and
> writebacks going on?

The above is just for providing command flags to user side, so that the
user side can understand/handle the request better.

prtrl(PR_SET_IO_FLUSHER) has been merged for avoiding the deadlock.

> 
> What are restriction on ubdsrv? What happens when it needs to allocate memory, or is
> swapped out?

Yeah, ubd_copy_pages() needs to pin pages for copying data between
user VM and block request pages, and get_user_pages may run out of pages.
But I think forward progress can still be provided by reserving one VM buffer
with single page locked.

> Have mm people seen this?

I remembered that the early RFC with related discussion is CCed to mm
list, and all follow-up are CC to linux-kernel.

Not one big deal, will Cc mm list in the future post.


thanks,
Ming


  reply	other threads:[~2022-06-02  3:20 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-09  9:23 [RFC PATCH] ubd: add io_uring based userspace block driver Ming Lei
2022-05-09 15:10 ` Gabriel Krisman Bertazi
2022-05-10  1:57   ` Ming Lei
2022-05-10  4:22   ` Ziyang Zhang
2022-05-09 16:00 ` Randy Dunlap
2022-05-09 18:11   ` Gabriel Krisman Bertazi
2022-05-09 18:13     ` Jens Axboe
2022-05-09 16:09 ` Jens Axboe
2022-05-10  2:58   ` Ming Lei
2022-05-10  3:29     ` Jens Axboe
2022-05-10  7:38       ` Ming Lei
2022-05-09 18:14 ` Martin Raiber
2022-05-16 19:29 ` Stefan Hajnoczi
2022-05-17  1:57   ` Ming Lei
2022-05-17  6:17     ` Stefan Hajnoczi
2022-05-30  7:07 ` Pavel Machek
2022-06-02  3:19   ` Ming Lei [this message]
2022-06-06  2:15     ` Gao Xiang

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