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

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Date:	Thu, 14 May 2015 17:06:39 -0700
From:	Daniel Phillips <daniel@...nq.net>
To:	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org
CC:	linux-fsdevel@...r.kernel.org, tux3@...3.org,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>, mgorman@...e.de,
	Andrea Arcangeli <aarcange@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [FYI] tux3: Core changes

Hi Rik,

Added Mel, Andrea and Peterz to CC as interested parties. There are
probably others, please just jump in.

On 05/14/2015 05:59 AM, Rik van Riel wrote:
> On 05/14/2015 04:26 AM, Daniel Phillips wrote:
>> Hi Rik,
>>
>> Our linux-tux3 tree currently currently carries this 652 line diff
>> against core, to make Tux3 work. This is mainly by Hirofumi, except
>> the fs-writeback.c hook, which is by me. The main part you may be
>> interested in is rmap.c, which addresses the issues raised at the
>> 2013 Linux Storage Filesystem and MM Summit 2015 in San Francisco.[1]
>>
>>    LSFMM: Page forking
>>    http://lwn.net/Articles/548091/
>>
>> This is just a FYI. An upcoming Tux3 report will be a tour of the page
>> forking design and implementation. For now, this is just to give a
>> general sense of what we have done. We heard there are concerns about
>> how ptrace will work. I really am not familiar with the issue, could
>> you please explain what you were thinking of there?
> 
> The issue is that things like ptrace, AIO, infiniband
> RDMA, and other direct memory access subsystems can take
> a reference to page A, which Tux3 clones into a new page B
> when the process writes it.
> 
> However, while the process now points at page B, ptrace,
> AIO, infiniband, etc will still be pointing at page A.
> 
> This causes the process and the other subsystem to each
> look at a different page, instead of at shared state,
> causing ptrace to do nothing, AIO and RDMA data to be
> invisible (or corrupted), etc...

Is this a bit like page migration?

Regards,

Daniel
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