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From: Stefan Hajnoczi <[email protected]>
To: "Denis V. Lunev" <[email protected]>
Cc: Ming Lei <[email protected]>,
	[email protected], [email protected],
	[email protected],
	Kirill Tkhai <[email protected]>,
	Manuel Bentele <[email protected]>,
	[email protected], Kevin Wolf <[email protected]>,
	[email protected], Xie Yongji <[email protected]>,
	Stefano Garzarella <[email protected]>,
	Josef Bacik <[email protected]>
Subject: Re: ublk-qcow2: ublk-qcow2 is available
Date: Wed, 5 Oct 2022 11:11:32 -0400	[thread overview]
Message-ID: <Yz2epPwoufj0mug/@fedora> (raw)
In-Reply-To: <[email protected]>

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On Tue, Oct 04, 2022 at 01:57:50AM +0200, Denis V. Lunev wrote:
> On 10/3/22 21:53, Stefan Hajnoczi wrote:
> > On Fri, Sep 30, 2022 at 05:24:11PM +0800, Ming Lei wrote:
> > > ublk-qcow2 is available now.
> > Cool, thanks for sharing!
> yep
> 
> > > So far it provides basic read/write function, and compression and snapshot
> > > aren't supported yet. The target/backend implementation is completely
> > > based on io_uring, and share the same io_uring with ublk IO command
> > > handler, just like what ublk-loop does.
> > > 
> > > Follows the main motivations of ublk-qcow2:
> > > 
> > > - building one complicated target from scratch helps libublksrv APIs/functions
> > >    become mature/stable more quickly, since qcow2 is complicated and needs more
> > >    requirement from libublksrv compared with other simple ones(loop, null)
> > > 
> > > - there are several attempts of implementing qcow2 driver in kernel, such as
> > >    ``qloop`` [2], ``dm-qcow2`` [3] and ``in kernel qcow2(ro)`` [4], so ublk-qcow2
> > >    might useful be for covering requirement in this field
> There is one important thing to keep in mind about all partly-userspace
> implementations though:
> * any single allocation happened in the context of the
>    userspace daemon through try_to_free_pages() in
>    kernel has a possibility to trigger the operation,
>    which will require userspace daemon action, which
>    is inside the kernel now.
> * the probability of this is higher in the overcommitted
>    environment
> 
> This was the main motivation of us in favor for the in-kernel
> implementation.

CCed Josef Bacik because the Linux NBD driver has dealt with memory
reclaim hangs in the past.

Josef: Any thoughts on userspace block drivers (whether NBD or ublk) and
how to avoid hangs in memory reclaim?

Stefan

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  reply	other threads:[~2022-10-05 15:12 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-30  9:24 ublk-qcow2: ublk-qcow2 is available Ming Lei
2022-10-03 19:53 ` Stefan Hajnoczi
2022-10-03 23:57   ` Denis V. Lunev
2022-10-05 15:11     ` Stefan Hajnoczi [this message]
2022-10-06 10:26       ` Ming Lei
2022-10-06 13:59         ` Stefan Hajnoczi
2022-10-06 15:09           ` Ming Lei
2022-10-06 18:29             ` Stefan Hajnoczi
2022-10-07 11:21               ` Ming Lei
2022-10-04  9:43   ` Ming Lei
2022-10-04 13:53     ` Stefan Hajnoczi
2022-10-05  4:18       ` Ming Lei
2022-10-05 12:21         ` Stefan Hajnoczi
2022-10-05 12:38           ` Denis V. Lunev
2022-10-06 11:24           ` Ming Lei
2022-10-07 10:04             ` Yongji Xie
2022-10-07 10:51               ` Ming Lei
2022-10-07 11:21                 ` Yongji Xie
2022-10-07 11:23                   ` Ming Lei
2022-10-08  8:43         ` Ziyang Zhang
2022-10-12 14:22           ` Stefan Hajnoczi
2022-10-13  6:48             ` Yongji Xie
2022-10-13 16:02               ` Stefan Hajnoczi
2022-10-14 12:56               ` Ming Lei
2022-10-17 11:11                 ` Yongji Xie
2022-10-18  6:59                   ` Ming Lei
2022-10-18 13:17                     ` Yongji Xie
2022-10-18 14:54                       ` Stefan Hajnoczi
2022-10-19  9:09                         ` Ming Lei
2022-10-24 16:11                           ` Stefan Hajnoczi
2022-10-21  5:33                         ` Yongji Xie
2022-10-21  6:30                           ` Jason Wang
2022-10-25  8:17                             ` Yongji Xie
2022-10-25 12:02                               ` Stefan Hajnoczi
2022-10-28 13:33                                 ` Yongji Xie
2022-11-01  2:36                                 ` Jason Wang
2022-11-02 19:13                                   ` Stefan Hajnoczi
2022-11-04  6:55                                     ` Jason Wang
2022-10-21  6:28                     ` Jason Wang
2022-10-06 10:14       ` Richard W.M. Jones
2022-10-12 14:15         ` Stefan Hajnoczi
2022-10-13  1:50           ` Ming Lei
2022-10-13 16:01             ` Stefan Hajnoczi
2022-10-04  5:43 ` Manuel Bentele

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