linux-kernel - Re: [PATCH] deflate inflate

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Message-ID: <463F91AF.6060005@zytor.com>
Date:	Mon, 07 May 2007 13:53:03 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>, Andi Kleen <ak@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Matt Mackall <mpm@...enic.com>
Subject: Re: [PATCH] deflate inflate_dynamic too

Jeremy Fitzhardinge wrote:
> H. Peter Anvin wrote:
>> It might be worth reverting some of the code back to the zlib original.
>>  The use of stack allocations here is actually a Linux divergence from
>> zlib (done by Linus), in order to reduce the number of dynamic allocations.
>>
>> In general, the use of dynamic allocations is highly dangerous, because
>> any time you have dynamic allocations you have the choice of either
>> sleeping or failing, unless you have a pre-reserved memory pool.
>>   
> 
> Well, every time this code is instantiated, it gets its own malloc/free
> definitions, so they can decide how to handle the dynamic allocations. 
> Seems better than assuming that every caller will have enough stack
> space.  If you want to approximate that, it would be easy enough to have
> a stack-like malloc/free, in which freeing the last allocation will
> always release space.

Indeed, however, the point still holds:

- Going to something more like the upstream zlib code makes it
worthwhile to see whatever else should be merged;
- Users must be audited for correctness.

In particular, it would be good to have a "preallocate me enough memory
so it can be guaranteed that this will succeed" operation.

	-hpa
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