[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] maybe revert commit c275a57f5ec3 "xen/balloon: Set balloon's initial state to number of existing RAM pages"
On 28/03/17 18:32, Boris Ostrovsky wrote: > On 03/28/2017 11:30 AM, Juergen Gross wrote: >> On 28/03/17 16:27, Boris Ostrovsky wrote: >>> On 03/28/2017 04:08 AM, Jan Beulich wrote: >>>>>>> On 28.03.17 at 03:57, <boris.ostrovsky@xxxxxxxxxx> wrote: >>>>> I think there is indeed a disconnect between target memory (provided by >>>>> the toolstack) and current memory (i.e actual pages available to the >>>>> guest). >>>>> >>>>> For example >>>>> >>>>> [ 0.000000] BIOS-e820: [mem 0x000000000009e000-0x000000000009ffff] >>>>> reserved >>>>> [ 0.000000] BIOS-e820: [mem 0x00000000000e0000-0x00000000000fffff] >>>>> reserved >>>>> >>>>> are missed in target calculation. The hvmloader marks them as RESERVED >>>>> (in build_e820_table()) but target value is not aware of this action. >>>>> >>>>> And then the same problem repeats when kernel removes >>>>> 0x000a0000-0x000fffff chunk. >>>> But this is all in-guest behavior, i.e. nothing an entity outside the >>>> guest (tool stack or hypervisor) should need to be aware of. That >>>> said, there is still room for improvement in the tools I think: >>>> Regions which architecturally aren't RAM (namely the >>>> 0xa0000-0xfffff range) would probably better not be accounted >>>> for as RAM as far as ballooning is concerned. In the hypervisor, >>>> otoh, all memory assigned to the guest (i.e. including such backing >>>> ROMs) needs to be accounted. >>> On the Linux side we should not include in balloon calculations pages >>> reserved by trim_bios_range(), i.e. (BIOS_END-BIOS_BEGIN) + 1. >>> >>> Which leaves hvmloader's special pages (and possibly memory under >>> 0xA0000 which may get reserved). Can we pass this info to guests via >>> xenstore? >> I'd rather keep an internal difference between online pages and E820-map >> count value in the balloon driver. This should work always. > > We could indeed base calculation on initial state of e820 and not count > the holes toward ballooning needs. I am not sure this will work for > memory unplug though, where a hole can be created in the map and we will > be supposed to handle disappearing memory via ballooning. > > Or am I creating a problem where none exists? I'm rather sure memory has to be offlined before being deleted from the E820 map. Juergen _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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