linux-ext4 - Re: [PATCH 1/3] fs: Introduce new flag FALLOC_FL_COLLAPSE

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Date:	Thu, 1 Aug 2013 10:23:41 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Theodore Ts'o <tytso@....edu>, Namjae Jeon <linkinjeon@...il.com>,
	adilger.kernel@...ger.ca, bpm@....com, elder@...nel.org,
	hch@...radead.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org,
	xfs@....sgi.com, a.sangwan@...sung.com,
	Namjae Jeon <namjae.jeon@...sung.com>
Subject: Re: [PATCH 1/3] fs: Introduce new flag FALLOC_FL_COLLAPSE_RANGE

On Wed, Jul 31, 2013 at 06:01:54PM -0400, Theodore Ts'o wrote:
> Have you considered what happens if you have a 10 megabyte file, of
> which the first 5 megs are mmap'ed into a userspace process.
> 
> Now suppose you call COLLAPASE_RANGE on a one megabyte range starting
> at offset 1024k from the beginning of the file.
> 
> Does the right thing happen to the mmap'ed region in memory?

Implementation detail. like a hole punch, it needs to invalidate the
range that it is operating over so mmap()d regions are refaulted
after the operation is done.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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