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

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Message-ID: <67294911-1776-46b8-916d-0e5642a38725@phunq.net>
Date:	Mon, 25 May 2015 23:11:11 -0700
From:	Daniel Phillips <daniel@...nq.net>
To:	David Lang <david@...g.hm>
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 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?

Regards,

Daniel

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