Re: [PATCH 0/5] Reducing fragmentation using zones

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

Mel Gorman wrote:
> To satisfy this request, I did a quick rebase of the list-based approach
> against 2.6.16-rc1-mm1 to have a comparable set of benchmarks. I will post
> the patches in the morning after a re-read.
Thank you.


> So, in terms of performance on this set of tests, both approachs perform
> roughly the same as the stock kernel in terms of absolute performance. In
> terms of high-order allocations, zone-based appears to do better under
> load. However, if you look at the zones that are used, you will see that
> zone-based appears to do as well as list-based *only* because it has the
> EASYRCLM zone to play with. list-based was way better at keeping the
> normal zone defragmented as well as highmem which is especially obvious
> when tested at rest.  list-based was able to allocate 83 huge pages from
> ZONE_NORMAL at rest while zone-based only managed 8.
yes, this is intersiting point :)
list-based one can defrag NORMAL zone.
The point will be "does we need to defrag NORMAL ?" , I think.
IMHO, I don't like to use NORMAL zone to alloc higher-order pages...

> Secondly, zone-based requires careful configuration to be successful.  If
> booted with kernelcore=896MB for example, it only performs slightly better
> than the standard kernel. If booted with kernelcore=1024MB, it tends to
> perform slightly worse (more zone fallbacks I guess) and still only
> manages slighly better satisfaction of high order pages.
This is because HIGHMEM is too small, right ?


> On the flip side, zone-based code changes are easier to understand than
> the list-based ones (at least in terms of volume of code changes). The
> zone-based gives guarantees on what will happen in the future while
> list-based is best-effort.
>
> In terms of fragmentation, I still think that list-based is better overall
> without configuration. 
I agree here.

> The results above also represent the best possible
> configuration with zone-based versus no configuration at all against
> list-based. In an environment with changing workloads a constant reality,
> I bet that list-based would win overall.
On x86, NORMAL is only 896M anyway. there is no discussion.


Honestly, I don't have enough experience with machines which doesn't have Highmem.
How large kernelcore should be ?
It looks using list-based and zone-based at the same time will make all people happy...

-- Kame

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