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From: Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH] fsync_range, was: Re: munmap, msync: synchronization
Date: Wed, 23 Apr 2014 08:45:50 -0700
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Cc: Christoph Hellwig <hch@infradead.org>,
	Jamie Lokier <jamie@shareable.org>,
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	Theodore T'so <tytso@mit.edu>,
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	Miklos Szeredi <miklos@szeredi.hu>
To: "Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
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On Wed, Apr 23, 2014 at 04:33:06PM +0200, Michael Kerrisk (man-pages) wrote:
> # Take journaling and atime out of the equation:
> 
> $ sudo umount /dev/sdb6
> $ sudo tune2fs -O ^has_journal /dev/sdb6$ 
> [sudo] password for mtk: 
> tune2fs 1.42.8 (20-Jun-2013)
> $ sudo mount -o norelatime,strictatime /dev/sdb6 /testfs

The second strictatime argument overrides the earlier norelatime,
so you put it into the picture.

> 
> But I have a question:
> 
> When I precreate a 10MB file, and repeat the tests (this time with 
> 100 loops), I no longer see any significant difference between 
> FFILESYNC and FDATASYNC. What am I missing? Sample runs here, 
> though I did the tests repeatedly with broadly similar results 
> each time:

Not sure.  Do you also see this on other filesystems?

> Add another question: is there any piece of sync_file_range() 
> functionality that could or should be incorporated in this API?

I don't think so.  sync_file_range is a complete mess and impossible
to use correctly for data integrity operations.  Especially the whole
notion that submitting I/O and waiting for it are separate operations
is incompatible with a data integrity call.