Re: ZONE_PADDING wastes 4 bytes of the new cacheline

[Nick Piggin <nickpiggin@yahoo.com.au>]

Andrew Morton wrote:
> Andrea Arcangeli <andrea@novell.com> wrote:
> 
>>I'm still unsure if the 2.6 lower_zone_protection completely mimics the
>> 2.4 lowmem_zone_reserve algorithm if tuned by reversing the pages_min
>> settings accordingly, but I believe it's easier to drop it and replace
>> with a clear understandable API that as well drops the pages_min levels
>> that have no reason to exists anymore
> 
> 
> I'd be OK with wapping over to the watermark version, as long as we have
> runtime-settable levels.
> 

Please no "wapping" over :) This release is the first time the allocator
has been anywhere near working properly in this area.

Of course, if Andrea shows that the ->protection racket isn't sufficient,
then yeah.

> But I'd be worried about making the default values anything other than zero
> because nobody seems to be hitting the problems.
> 
> But then again, this get discussed so infrequently that by the time it
> comes around again I've forgotten all the previous discussion.  Ho hum.
> 

I think they probably should be turned on. A system with a gig of ram
shouldn't be able to use up all of ZONE_DMA on pagecache. It seems like
a small price to pay... same goes for very big highmem systems and ZONE_NORMAL.