Re: [Lhms-devel] [PATCH 0/7] Fragmentation Avoidance V19

[Linus Torvalds <torvalds@osdl.org>]

On Thu, 3 Nov 2005, Martin J. Bligh wrote:
> 
> Ha. Just because I don't think I made you puke hard enough already with
> foul approximations ... for order 2, I think it's

Your basic fault is in believing that the free watermark would stay 
constant.

That's insane.

Would you keep 8MB free on a 64MB system?

Would you keep 8MB free on a 8GB system?

The point being, that if you start with insane assumptions, you'll get 
insane answers.

The _correct_ assumption is that you aim to keep some fixed percentage of 
memory free. With that assumption and your math, finding higher-order 
pages is equally hard regardless of amount of memory. 

Now, your math then doesn't allow for the fact that buddy automatically 
coalesces for you, so in fact things get _easier_ with more memory, but 
hey, that needs more math than I can come up with (I never did it as math, 
only as simulations with allocation patterns - "smart people use math, 
plodding people just try to simulate an estimate" ;)

		Linus
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/