Re: [PATCH 08/10] dm-integrity: add a bitmap mode

[Mike Snitzer <snitzer@redhat.com>]

On Wed, May 08 2019 at 12:46pm -0400,
Mikulas Patocka <mpatocka@redhat.com> wrote:

> 
> 
> On Tue, 7 May 2019, Mike Snitzer wrote:
> 
> > On Mon, Apr 29 2019 at  8:57am -0400,
> > Mikulas Patocka <mpatocka@redhat.com> wrote:
> > 
> > > Add a new bitmap mode for dm-integrity.
> > > 
> > > Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
> > 
> > This patch header needs much more detail.
> > 
> > Can you please be as informative and detailed as possible about what
> > this new bitmap mode is (what constraints it has, where it is expected
> > to be useful, etc)?  Also, if you have them, provide some benchmarks
> > that showcase its benefits.
> > 
> > Thanks,
> > Mike
> 
> The patch adds the documentation to the file 
> "Documentation/device-mapper/dm-integrity.txt", so it can be also used as 
> a patch header. For example:
> 
> "This patch introduces an alternative mode of operation whete dm-integrity 
> uses bitmap instead of a journal. If a bit in the bitmap is 1, the 
> corresponding region's data and integrity tags are not synchronized - if 
> the machine crashes, the unsynchronized regions will be recalculated. The 
> bitmap mode is faster than the journal mode, because we don't have to 
> write the data twice, but it is also less reliable, because if data 
> corruption happens when the machine crashes, it may not be detected."
> 
> Benchmark - on an SSD connected to a SATA300 port, when doing large linear 
> writes with dd.
> 
> buffered I/O:
> 	raw device throughput - 245MB/s
> 	dm-integrity with journaling - 120MB/s
> 	dm-integrity with bitmap - 238MB/s
> 
> direct I/O with 1MB block size:
> 	raw device throughput - 248MB/s
> 	dm-integrity with journaling - 123MB/s
> 	dm-integrity with bitmap - 223MB/s

Great, thanks.