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List:       busybox
Subject:    Re: open_transformer fork, depmod
From:       walter harms <wharms () bfs ! de>
Date:       2014-11-25 18:41:06
Message-ID: 5474CD42.60205 () bfs ! de
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Am 25.11.2014 18:25, schrieb Lauri Kasanen:
> Hi,
> 
> Can anyone fill me in on the reason why open_transformer always forks,
> instead of straight decompressing?
> 
> I found the original commit from 2003:
> http://lists.busybox.net/pipermail/busybox-cvs/2003-November/019040.html
> But it doesn't explain why the move was done.
> 
> I ask because doing a "depmod -a" with gzipped modules results in over
> 800 forks, which is surely not optimal neither from memory nor from
> performance points of view.
> 
> In the case of gzip, the uncompressed size is available, so there would
> be no RAM waste in allocating the maximum specified 64mb first. For
> compression formats that do not include the uncompressed size, the
> fork+pipe approach does save RAM, but for gzip it seems to be needless
> overhead.
> 
> - Lauri
> 

hi Lauri,
so far i understand is the code idea to pipe the daten before doing the work,
fine for tar (like: gzcat file | tar -xzf-)
i guess that was done to avoid creating an gunzip function call.
In the moddep case this will result in calling the gzcat everytime a compressed module is
found. Maybe you can make a special function that extracts only the required information
and the drops the rest.

re,
 wh


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