Re: -mmX 4G patches feedback [numbers: how much performance impact]

[Andrea Arcangeli <andrea@suse.de>]

On Thu, Apr 08, 2004 at 04:14:08PM -0700, Martin J. Bligh wrote:
> Me confused. Are you saying it's worse compared to pte_highmem? or to 
> shoving ptes in lowmem?

worse than pte_highmem if booting with mem=800m

> Ah. You're worried about the distro situation, where PTE_HIGHMEM would
> be turned on for a non-highmem machine, right? Makes more sense I guess.

it's not just a distro situation, it's about not having to recompile the
kernel for every machine I own, even gentoo has an option to have a
compile server in the network that build packages and you install the
binaries from it, so there must be some value in being able to share a
binary on more than one machine (this is especially true for me since I
upgrade kernel quite fast).

it's not just about non-highmem machines, on 1G/2G boxes the probability
that pte-highmem cause you any slowdown is an order of magnitude smaller
than on a 32G machine (where ptes should never hit lowmem or it means my
classzone lowmem_reserve_ratio algorithms have not yet been ported to 2.6)
with your model you'd have no way to boost when you are lucky to get a
lowmem page.