linux-kernel - Re: [RFC PATCH] greatly reduce SLOB external fragmentation

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Date:	Thu, 31 Jul 2008 04:42:16 +0400
From:	malc@...sesoft.com
To:	linux-kernel@...r.kernel.org
Subject:  Re: [RFC PATCH] greatly reduce SLOB external fragmentation

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> On Thu, 31 Jul 2008, Pekka Enberg wrote:
>> 
>> Oh, I didn't suggest this for merging. Just thought you'd be
>> interested to know that best-fit doesn't really do that much better
>> than what we have in the tree now. (Well, I was kinda hoping you'd
>> tell me why my implementation is wrong and you were right all along.)
>
> Heh. Most allocators tend to work pretty well under normal load, and the 
> real fragmentation problems all tend to happen under special patterns. The 
> one in glibc, for example, sucks donkey dick when using threading, but is 
> apparently ok otherwise. 
>
> I wouldn't actually expect most "normal" kernel use to show any really bad 
> patterns on any normal loads. Google for
>
> 	worst-case first-fit fragmentation
>
> (or 'next-fit' for that matter) to see some stuff. Of course, it is scary 
> only if you can trigger it in practice (perhaps with certains games on 
> packet size, or creating/removing files with pathname size patterns ec).
>
> [ Of course, google probably mostly returns hits from all those ACM 
>   portals etc. I wonder why google does that - they're almost totally 
>   useless search results. Sad. If somebody knows how to turn those ACM 
>   pay-portals off in google, pls let me know ]
>
> 			Linus

blahblah -site:portal.acm.org ?

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