Re: 2.6.0 Huge pages not working as expected

[Linus Torvalds <torvalds@osdl.org>]

On Sat, 27 Dec 2003, Andrea Arcangeli wrote:
> 
> well, at least on the alpha the above mode = 1 is reproducibly a lot
> better (we're talking about a wall time 2/3 times shorter IIRC) than
> random placement. The l2 is huge and one way cache associative,

What kind of strange and misguided hw engineer did that?

I can understand a one-way L1, simply to keep the cycle time low, but 
what's the point of a one-way L2? Braindead external cache controller?

> The current patch is for 2.2 with an horrible API (it uses a kernel
> module to set those params instead of a sysctl, despite all the real
> code is linked into the kernel), while developing it I only focused on
> the algorithms and the final behaviour in production. the engine to ask
> the allocator a page of the right color works O(1) with the number of
> free pages and it's from Jason.

Does it keep fragmentation down?

That's the problem that Davem had in one of his cache-coloring patches: it
worked well enough if you had lots of memory, but it _totally_ broke down
when memory was low. You couldn't allocate higher-order pages at all after
a while because of the fragmented memory.

			Linus