Re: Avoiding external fragmentation with a placement policy Version12

From: Nick Piggin
Date: Wed Jun 01 2005 - 19:26:04 EST


Mike Kravetz wrote:
On Thu, Jun 02, 2005 at 09:09:23AM +1000, Nick Piggin wrote:

It adds a lot of complexity to the page allocator and while
it might be very good, the only improvement we've been shown
yet is allocating lots of MAX_ORDER allocations I think? (ie.
not very useful)



Allocating lots of MAX_ORDER blocks can be very useful for things
like hot-pluggable memory. I know that this may not be of interest
to most. However, I've been combining Mel's defragmenting patch
with the memory hotplug patch set. As a result, I've been able to
go from 5GB down to 544MB of memory on my ppc64 system via offline
operations. Note that ppc64 only employs a single (DMA) zone. So,
page 'grouping' based on use is coming mainly from Mel's patch.


Back in the day, Linus would tell you to take a hike if you
wanted to complicate the buddy allocator to better support
memory hotplug ;)

I don't know what's happened to him now though, he seems to
have gone a little soft on you enterprise types.

Seriously - thanks for the data point, I had an idea that you
guys wanted this for mem hotplug.

--
SUSE Labs, Novell Inc.

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