Re: [discuss] Re: 32-bit dma allocations on 64-bit platforms

[Andrea Arcangeli <andrea@suse.de>]

On Thu, Jun 24, 2004 at 09:56:29AM -0700, William Lee Irwin III wrote:
> On Fri, Jun 25, 2004 at 01:48:47AM +1000, Nick Piggin wrote:
> >> 2.6 has the "incremental min" thing. What is wrong with that?
> >> Though I think it is turned off by default.
> 
> On Thu, Jun 24, 2004 at 06:52:01PM +0200, Andrea Arcangeli wrote:
> > sysctl_lower_zone_protection is an inferior implementation of the
> > lower_zone_reserve_ratio, inferior because it has no way to give a
> > different balance to each zone. As you said it's turned off by default
> > so it had no tuning. The lower_zone_reserve_ratio has already been
> > tuned in 2.4. Somebody can attempt a conversion but it'll never be equal
> > since lower_zone_reserve_ratio is a superset of what
> > sysctl_lower_zone_protection can do.
> 
> Is there any chance you could send in thise improved implementation of
> zone fallback watermarks and describe the deficiencies in the current
> scheme that it corrects?

I did quite a few times and it was successfully merged in 2.4. Now I'd
need to forward port to 2.6.

I recall I recommended Andrew to merge the lower_zone_reserve_ratio
at some point during 2.5 or early 2.6 but apparently he implemented this
other thing called sysctl_lower_zone_protection. Note that now that I
look more into it, it seems sysctl_lower_zone_protection and
lower_zone_reserve_ratio have very little in common, I'm glad
sysctl_lower_zone_protection is disabled.  sysctl_lower_zone_protection
is just an improvement to the algorithm I dropped from 2.4 when
lowmem_zone_reserve_ratio was merged.  So in short enabling
sysctl_lower_zone_protection won't help, sysctl_lower_zone_protection
should be dropped enterely and replaced with lower_zone_reserve_ratio.