Re: Reiser4 documentation & specifically current status of repacker, compression, and semantics

[Hans Reiser <reiser@namesys.com>]

Edward Shishkin wrote:

> Hans Reiser wrote:
>
>> John Gilmore wrote:
>>
>>> So the first beta of compression will only have the option to
>>> control it at mkfs time?
>>>
>>>   
>>
>> It should be explained that on the first flush to disk of a new file the
>> default compress plugin will test to see if the first 64k is
>> compressable, and if it is not then it converts the file to a regular
>> file plugin.
>>
>>  
>>
>
> a little correction:
> this is a compression transform plugin that is converted at flush
> time, not file plugin
>
Please define in more detail please.  Particularly, define whether large
files that cannot be compressed get stored using extents and everything
else that regular files use.

Also, I thought we convert at first flush time, not at every flush
time.  Did you write it to check at every flush?  Not entirely sure we
want to do that for large multimedia files that are compressed by
hardware, it could add a bunch of CPU, and I would think it would be
more complex code, because now you have to convert extents, etc.  I
would be concerned that if you always have to check for compression with
every little write to a file, the cost of that check will be substantial
for many purposes.

Hans