On 08/10/2017 03:25 PM, Hugo Mills wrote:
On Thu, Aug 10, 2017 at 01:41:21PM -0400, Chris Mason wrote:
On 08/10/2017 04:30 AM, Eric Biggers wrote:

Theses benchmarks are misleading because they compress the whole file as a
single stream without resetting the dictionary, which isn't how data will
typically be compressed in kernel mode.  With filesystem compression the data
has to be divided into small chunks that can each be decompressed independently.
That eliminates one of the primary advantages of Zstandard (support for large
dictionary sizes).

I did btrfs benchmarks of kernel trees and other normal data sets as
well.  The numbers were in line with what Nick is posting here.
zstd is a big win over both lzo and zlib from a btrfs point of view.

It's true Nick's patches only support a single compression level in
btrfs, but that's because btrfs doesn't have a way to pass in the
compression ratio.  It could easily be a mount option, it was just
outside the scope of Nick's initial work.

    Could we please not add more mount options? I get that they're easy
to implement, but it's a very blunt instrument. What we tend to see
(with both nodatacow and compress) is people using the mount options,
then asking for exceptions, discovering that they can't do that, and
then falling back to doing it with attributes or btrfs properties.
Could we just start with btrfs properties this time round, and cut out
the mount option part of this cycle.

    In the long run, it'd be great to see most of the btrfs-specific
mount options get deprecated and ultimately removed entirely, in
favour of attributes/properties, where feasible.

It's a good point, and as was commented later down I'd just do mount -o compress=zstd:3 or something.

But I do prefer properties in general for this. My big point was just that next step is outside of Nick's scope.


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