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

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Date:	Fri, 15 May 2015 09:05:12 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Daniel Phillips <daniel@...nq.net>
Cc:	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, tux3@...3.org,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [FYI] tux3: Core changes

On Thu, May 14, 2015 at 05:06:39PM -0700, Daniel Phillips wrote:
> 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?
> 

No, it's not.

-- 
Mel Gorman
SUSE Labs
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