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
next prev parent 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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