Re: [RFC PATCH] greatly reduce SLOB external fragmentation

Linus Torvalds
2008-07-30T22:39:50Z

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