[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [RFC PATCH] page_alloc: use first half of higher order chunks when halving
On Fri, Apr 11, 2014 at 01:28:45PM -0700, Matthew Rushton wrote: > On 04/11/14 10:05, Konrad Rzeszutek Wilk wrote: > >On Wed, Apr 09, 2014 at 03:21:38PM -0700, Matthew Rushton wrote: > >>On 04/02/14 03:20, Ian Campbell wrote: > >>>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. > >>OK understood see below. > >> > >>>>>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. > >>I think you're missing the point. I'm not arguing that this change > >>is a general purpose solution to guarantee that dom0 is contiguous. > >>Fragmentation can exist even if dom0 asks for larger allocations > >>like it should (which the balloon driver does I believe). What the > >>change does do is solve a real problem in the current Linux PCI > >>remapping implementation which happens during dom0 intialization. If > >>the allocation strategy is arbitrary why not make the proposed > >>hypervisor change to make existing Linux implementations behave > >>better and in addition fix the problem in Linux so moving forward > >>things are safe? > >I think Tim was OK with that - as long as it was based on a flag - meaning > >when we do the increase_reservation call we use an extra flag > >to ask for contingous PFNs. > > OK the extra flag feels a little dirty to me but it would solve the > problem. What are your thoughts on changing Linux to make higher > order allocations or more minimally adding a boot parameter to not > remap the memory at all for those that care about performance? I Oh, so just leave it ballooned down? I presume you can get the same exact behavior if you have your dom0_mem=max:X value tweaked just right? And your E820 does not look like swiss cheese. > know the Linux code is already fairly complex and your preference > was not to make it worse. > > >>>Ian. > >>> > >> > >>_______________________________________________ > >>Xen-devel mailing list > >>Xen-devel@xxxxxxxxxxxxx > >>http://lists.xen.org/xen-devel > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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