[GSOC] HAMMER2 compression feature week1 report

[Daniel Flores]

On Sun, Jul 28, 2013 at 9:53 PM, Radio młodych bandytów <
radiomlodychbandytow at o2.pl> wrote:

> On 28/07/2013 21:08, Daniel Flores wrote:
> > we don't reference previous blocks at this moment
> Do you intend to add it? How?
>

At this moment I don't have plans regarding previous blocks, but maybe in
the course of optimizing the write path there will be some ideas about it.
We'll see.


> No, they are not the same, but in a way that doesn't matter here - I set
>  'sector size' to 32 KB, so even if a block compresses to less than 16,
> it takes 32 KB.
> I checked, the tail block compressed from 47875 to 32038.
>

Oh, I understand now why you got that block compressed and I didn't.
It's just that my prototype application, that I used to test this algorithm
and generate my test results, always tries to compress a whole 64KB block.
So, in this case, instead of trying to compress just 47875 bytes of data,
it tried to compress a block that contained that data and also some
garbage, which, logically, didn't lead to a successful compression.


> If you're open to researching other algorithm options, I suggest looking
>  at fsbench, it's going to be easier to adapt it to the way HAMMER2 works
> than to add other algorithms to the kernel:
> http://encode.ru/threads/1371-Filesystem-benchmark?highlight=fsbench
> Note that the latest version crashes on your book2 with settings as
> above, you made me find an integer underflow. Will upload an update
> later today.
>

OK, this looks really interesting. This application can make the process of
testing an algorithm a lot easier.
I'll take a closer look at it soon.

Thank you.


Daniel
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