Re: [Xen-devel] [RFC PATCH] page_alloc: use first half of higher order chunks when halving

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2014-04-02 at 11:15 +0100, Jan Beulich wrote:
> >>> On 02.04.14 at 12:06, <Ian.Campbell@xxxxxxxxxx> wrote:
> > On Wed, 2014-04-02 at 08:52 +0100, Jan Beulich wrote:
> >> >>> On 02.04.14 at 02:17, <mvrushton@xxxxxxxxx> wrote:
> >> > On 04/01/14 05:22, Tim Deegan wrote:
> >> >> As long as we don't also change the default allocation order in
> >> >> Xen. :)  In general, linux shouldn't rely on the order that Xen
> >> >> allocates memory, as that might change later.  If the current API
> >> >> can't do what's needed, maybe we can add another allocator
> >> >> hypercall or flag?
> >> > 
> >> > Agree on not relying on the order in the long run. A new hypercall or 
> >> > flag seems like overkill right now. The question for me comes down to my 
> >> > proposed change which is more simple and solves the short term problem 
> >> > or investing time in reworking the Linux code to make large allocations.
> >> 
> >> I think it has become pretty clear by now that we'd rather not alter
> >> the hypervisor allocator for a purpose like this.
> > 
> > Does it even actually solve the problem? It seems like it is just
> > deferring it until sufficient fragmentation has occurred in the system.
> > All its really done is make the eventual issue much harder to debug.
> 
> Wasn't this largely for Dom0 (in which case fragmentation shouldn't
> matter yet)?

Dom0 ballooning breaks any assumptions you might make about relying on
early allocations.

Ian.


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