Re: The performance and behaviour of the anti-fragmentation related patches

[Joel Schopp <jschopp@austin.ibm.com>]

> But if you don't require a lot of higher order allocations anyway, then
> guest fragmentation caused by ballooning doesn't seem like much problem.

If you only need to allocate 1 page size and smaller allocations then no it's not a 
problem.  As soon as you go above that it will be.  You don't need to go all the way 
up to MAX_ORDER size to see an impact, it's just increasingly more severe as you get 
away from 1 page and towards MAX_ORDER.

> 
> If you need higher order allocations, then ballooning is bad because of
> fragmentation, so you need memory unplug, so you need higher order
> allocations. Goto 1.

Yes, it's a closed loop.  But hotplug isn't the only one that needs higher order 
allocations.  In fact it's pretty far down the list.  I look at it like this, a lot 
of users need high order allocations for better performance and things like on-demand 
hugepages.  As a bonus you get memory hot-remove.

> Balooning probably does skew memory management stats and watermarks, but
> that's just because it is implemented as a module. A couple of hooks
> should be enough to allow things to be adjusted?

That is a good idea independent of the current discussion.