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From: "Figo.zhang" <figo1802@gmail.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: lsf-pc@lists.linux-foundation.org, Linux MM <linux-mm@kvack.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	linux-block@vger.kernel.org
Subject: Re: [LSF/MM TOPIC] A high-performance userspace block driver
Date: Thu, 18 Jan 2018 13:27:24 +0800	[thread overview]
Message-ID: <CAF7GXvonnUNGMWXnR1gM0LhqQ_gjktcv50V7WGdBtbufbc-8eg@mail.gmail.com> (raw)
In-Reply-To: <20180116145240.GD30073@bombadil.infradead.org>

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2018-01-16 22:52 GMT+08:00 Matthew Wilcox <willy@infradead.org>:

>
> I see the improvements that Facebook have been making to the nbd driver,
> and I think that's a wonderful thing.  Maybe the outcome of this topic
> is simply: "Shut up, Matthew, this is good enough".
>
> It's clear that there's an appetite for userspace block devices; not for
> swap devices or the root device, but for accessing data that's stored
> in that silo over there, and I really don't want to bring that entire
> mess of CORBA / Go / Rust / whatever into the kernel to get to it,
> but it would be really handy to present it as a block device.
>
> I've looked at a few block-driver-in-userspace projects that exist, and
> they all seem pretty bad.


how about the SPDK?


> For example, one API maps a few gigabytes of
> address space and plays games with vm_insert_page() to put page cache
> pages into the address space of the client process.  Of course, the TLB
> flush overhead of that solution is criminal.
>
> I've looked at pipes, and they're not an awful solution.  We've almost
> got enough syscalls to treat other objects as pipes.  The problem is
> that they're not seekable.  So essentially you're looking at having one
> pipe per outstanding command.  If yu want to make good use of a modern
> NAND device, you want a few hundred outstanding commands, and that's a
> bit of a shoddy interface.
>
> Right now, I'm leaning towards combining these two approaches; adding
> a VM_NOTLB flag so the mmaped bits of the page cache never make it into
> the process's address space, so the TLB shootdown can be safely skipped.
> Then check it in follow_page_mask() and return the appropriate struct
> page.  As long as the userspace process does everything using O_DIRECT,
> I think this will work.
>
> It's either that or make pipes seekable ...
>
> --
> To unsubscribe, send a message with 'unsubscribe linux-mm' in
> the body to majordomo@kvack.org.  For more info on Linux MM,
> see: http://www.linux-mm.org/ .
> Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
>

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      parent reply	other threads:[~2018-01-18  5:27 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-16 14:52 Matthew Wilcox
2018-01-16 23:04 ` Viacheslav Dubeyko
2018-01-16 23:23 ` Theodore Ts'o
2018-01-16 23:28   ` [Lsf-pc] " James Bottomley
2018-01-16 23:57     ` Bart Van Assche
2018-01-17  0:41 ` Bart Van Assche
2018-01-17  2:49 ` Ming Lei
2018-01-17 21:21   ` Matthew Wilcox
2018-01-22 12:02     ` Mike Rapoport
2018-01-22 12:18     ` Ming Lei
2018-01-18  5:27 ` Figo.zhang [this message]

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