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

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Message-ID: <alpine.DEB.2.02.1505252312570.3147@nftneq.ynat.uz>
Date:	Mon, 25 May 2015 23:13:46 -0700 (PDT)
From:	David Lang <david@...g.hm>
To:	Daniel Phillips <daniel@...nq.net>
cc:	Rik van Riel <riel@...hat.com>, Jan Kara <jack@...e.cz>,
	linux-fsdevel@...r.kernel.org, tux3@...3.org,
	linux-kernel@...r.kernel.org,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Subject: Re: [FYI] tux3: Core changes

On Mon, 25 May 2015, Daniel Phillips wrote:

> On Monday, May 25, 2015 11:04:39 PM PDT, David Lang wrote:
>> if the page gets modified again, will that cause any issues? what if the 
>> page gets modified before the copy gets written out, so that there are two 
>> dirty copies of the page in the process of being written?
>> 
>> David Lang
>
> How is the page going to get modified again? A forked page isn't
> mapped by a pte, so userspace can't modify it by mmap. The forked
> page is not in the page cache, so usespace can't modify it by
> posix file ops. So the writer would have to be in kernel. Tux3
> knows what it is doing, so it won't modify the page. What kernel
> code besides Tux3 will modify the page?

I'm assuming that Rik is talking about whatever has the reference to the page 
via one of the methods that he talked about.

David Lang
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