Re: [lc-devel] Compressing a page using WKdm

[Nitin G. <nit...@gm...>]

On 6/9/06, Anderson Briglia <bri...@gm...> wrote:
> > > I have been trying to compress a page using that WKdm code from
> > > project's CVS. But, something is wrong because the system hangs after
> > > some compression/decompression pages. I'm using this interface:
> > >
> > > to compress "original_page":
> > >
> > > int len;
> > > len = WKdm_compress(page_address(original_page), page_address(comp_page), 1024);
> > > memcpy(page_address(original_page), page_address(comp_page), len);
> > >
> > > to decompress:
> > >
> > > WKdm_decompress(page_address(original_page), page_address(decomp_page), 1024);
> > > memcpy(page_address(original_page), page_address(decomp_page), PAGE_SIZE);
> > >
> > > Is needed to do some padding? I saw at compress_test module that the
> > > comp_data is filled with 0's after the compression. Is it necessary?
> >
> > Yes, WKdm only works when input is exactly 1024 words.
>
> So, I guess I must do a loop if I want to compress one page-full of
> data, right? A loop of four iteractions, of course.
>

No, I meant 1024 words==PAGE_SIZE (4K bytes). WKdm needs input of 4K
bytes to work so you can compress a page with a single call.

> > Are you compressing pages with less than page-full of data and still without
> > padding?
>
> I'm compressing pages came from the shrink_list( ). I believe those
> pages have PAGE_SIZE of data.
>

Are you just compressing and discarding pages as they come in
shrink_list() or have you developed any compression structure to store
pages and then later restore them when lookup is performed?


Cheers,
Nitin Gupta