Re: Page allocator: Single Zone optimizations

[Andy Whitcroft <apw@shadowen.org>]

Andrew Morton wrote:
> On Wed, 1 Nov 2006 22:10:02 +0000 (GMT)
> Mel Gorman <mel@csn.ul.ie> wrote:
> 
>> On Wed, 1 Nov 2006, Andrew Morton wrote:
>>
>>> On Wed, 1 Nov 2006 18:26:05 +0000
>>> mel@skynet.ie (Mel Gorman) wrote:
>>>
>>>> I never really got this objection. With list-based anti-frag, the
>>>> zone-balancing logic remains the same. There are patches from Andy
>>>> Whitcroft that reclaims pages in contiguous blocks, but still with the same
>>>> zone-ordering. It doesn't affect load balancing between zones as such.
>>> I do believe that lumpy-reclaim (initiated by Andy, redone and prototyped
>>> by Peter, cruelly abandoned) is a perferable approach to solving the
>>> fragmentation approach.
>>>
>> On it's own lumpy-reclaim or linear-reclaim were not enough to get 
>> MAX_ORDER_NR_PAGES blocks of contiguous pages and these were of interest 
>> for huge pages although not necessarily of much use to memory hot-unplug. 
> 
> I'm interested in lumpy-reclaim as a simple solution to the
> e1000-cant-allocate-an-order-2-page problem, rather than for hugepages.
> 
> ie: a bugfix, not a feature..


Is there a description of the problem and particularly of the
allocation patterns here.  Particularly key is the level
of memory pressure when we are allocating these higher orders.
Lumpy reclaim and less so Linear reclaim is less effective when
memory pressure is severe so we may not see the hoped for benefit.
Most of the benchmarking we have done is for higher order pages
and this effect may well be less at lower order.

-apw

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