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Date: Sat, 10 Sep 2016 00:40:34 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Amir Goldstein <amir73il@gmail.com>,
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Subject: Re: [PATCH] ovl: use copy_file_range for copy up if possible
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On Sat, Sep 10, 2016 at 09:52:21AM +1000, Dave Chinner wrote:
> > vfs_copy_file_range() implementation because ovl_copy_up_data()
> > splices in small chunks allowing the user to kill the copying process.
> > This makes sense because the poor process only called open(),
> > so the app writer may not have been expecting a stall of copying
> > a large file...
> 
> So call vfs_copy_file_range() iteratively, just like is being done
> right now for do_splice_direct() to limit latency on kill.

I wish vfs_copy_file_range would do useful chinking itself.

But either way it might be a good idea to call vfs_clone_file_range
first, because that gives your a very efficient copy without the need
to copy anything if supported.