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

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Message-ID: <alpine.DEB.2.02.1505252303120.3147@nftneq.ynat.uz>
Date:	Mon, 25 May 2015 23:04:39 -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 9:25:44 PM PDT, Rik van Riel wrote:
>> On 05/21/2015 03:53 PM, Daniel Phillips wrote:
>>> On Wednesday, May 20, 2015 8:51:46 PM PDT, David Lang wrote:
>>>> how do you prevent it from continuing to interact with the old version
>>>> of the page and never see updates or have it's changes reflected on
>>>> the current page?
>>> 
>>> Why would it do that, and what would be surprising about it? Did
>>> you have a specific case in mind?
>> 
>> After a get_page(), page_cache_get(), or other equivalent
>> function, a piece of code has the expectation that it can
>> continue using that page until after it has released the
>> reference count.
>> 
>> This can be an arbitrarily long period of time.
>
> It is perfectly welcome to keep using that page as long as it
> wants, Tux3 does not care. When it lets go of the last reference
> (and Tux3 has finished with it) then the page is freeable. Did
> you have a more specific example where this would be an issue?
> Are you talking about kernel or userspace code?

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
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