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Re: [PATCH 1/3] fs: Introduce new flag FALLOC_FL_COLLAPSE_RANGE

To: Theodore Ts'o <tytso@xxxxxxx>, Namjae Jeon <linkinjeon@xxxxxxxxx>, adilger.kernel@xxxxxxxxx, bpm@xxxxxxx, elder@xxxxxxxxxx, hch@xxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-ext4@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx, a.sangwan@xxxxxxxxxxx, Namjae Jeon <namjae.jeon@xxxxxxxxxxx>
Subject: Re: [PATCH 1/3] fs: Introduce new flag FALLOC_FL_COLLAPSE_RANGE
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Thu, 1 Aug 2013 10:23:41 +1000
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130731220154.GA11378@xxxxxxxxx>
References: <1375281721-15840-1-git-send-email-linkinjeon@xxxxxxxxx> <20130731220154.GA11378@xxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
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.


Dave Chinner

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