Re: Linux Kernel Dump Summit 2005

Pavel Machek
2005-10-10T08:45:58Z

Hi!

> FULL DUMP WITH COMPRESSION
> ==========================
>
> Those who still want a full dump, including me, are interested
> in dump compression. For example, the LKCD format (at least v7
> format) supports pagewise compression with the deflate
> algorithm. A dump analyze tool "crash" can transparently
> analyze the compressed dump file in this format.
>
> The compression will reduce the storage space at certain degree,
> and may also reduce the time if a dump process were I/O bounded.

I'd say that compression does not help much, it can only speed it up
twice. But...

>
> WHICH IS BETTER?
> ================
>
> I wrote a small compression tool for LKCD v7 format to see how
> effective the compression is, and it turned out that the time
> and size of compression were very much similar to that of gzip,
> not surprisingly.
>
> Compressing a 32GB dump file took about 40 minutes on Pentium 4
> Xeon 3.0GHz, which is not good enough because the dump without
> compression took only 5 minutes; eight times slower.

....you probably want to look at suspend2.net project. They have
special compressor aimed at compressing exactly this kind of data,
fast enough to be improvement.
Pavel

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