linux-kernel - Re: [FYI] tux3: Core changes

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Message-ID: <55D35FC6.9000005@redhat.com>
Date:	Tue, 18 Aug 2015 12:39:34 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Daniel Phillips <daniel@...nq.net>,
	Raymond Jennings <shentino@...il.com>
CC:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	David Lang <david@...g.hm>, Jan Kara <jack@...e.cz>,
	tux3@...3.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [FYI] tux3: Core changes

On 07/31/2015 01:27 PM, Daniel Phillips wrote:
> On Friday, July 31, 2015 8:37:35 AM PDT, Raymond Jennings wrote:
>> Returning ENOSPC when you have free space you can't yet prove is safer
>> than
>> not returning it and risking a data loss when you get hit by a
>> write/commit
>> storm. :)
>
> Remember when delayed allocation was scary and unproven, because proving
> that ENOSPC will always be returned when needed is extremely difficult?
> But the performance advantage was compelling, so we just worked at it
> until it worked. There were times when it didn't work properly, but the
> code was in the tree so it got fixed.
>
> It's like that now with page forking - a new technique with compelling
> advantages, and some challenges. In the past, we (the Linux community)
> would rise to the challenge and err on the side of pushing optimizations
> in early. That was our mojo, and that is how Linux became the dominant
> operating system it is today. Do we, the Linux community, still have that
> mojo?

Do you have the mojo to come up with a proposal on how
to make things work, in a way that ensures data consistency
for Linux users?

Yes, we know page forking is not compatible with the way
Linux currently uses refcounts.

The question is, does anyone have an idea on how we could
fix that?

Not necessarily an implementation yet, just an idea might
be enough to move forward at this stage.

However, if nobody wants to work on even an idea, page
forking may simply not be a safe thing to do.

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