Re: [libvirt] [PATCH V2] qemu: Redefine the "unlimited" memory limits one more time

On Fri, Nov 25, 2016 at 05:12:41PM +0100, Martin Kletzander wrote: > On Fri, Nov 25, 2016 at 03:39:17PM +0000, Daniel P. Berrange wrote: >> On Fri, Nov 25, 2016 at 04:35:14PM +0100, Martin Kletzander wrote: >>> On Fri, Nov 25, 2016 at 03:19:54PM +0100, Viktor Mihajlovski wrote: >>>> On 18.11.2016 17:44, Viktor Mihajlovski wrote: >>>>> With kernel 3.18 (since commit 3e32cb2e0a12b6915056ff04601cf1bb9b44f967) the >>>>> "unlimited" value for cgroup memory limits has changed once again as its byte >>>>> value is now computed from a page counter. >>>>> The new "unlimited" value reported by the cgroup fs is therefore 2**51-1 pages >>>>> which is (VIR_DOMAIN_MEMORY_PARAM_UNLIMITED - 3072). This results e.g. in virsh >>>>> memtune displaying 9007199254740988 instead of unlimited for the limits. >>>>> >>> >>> Ah, I wonder hoe many times we'll have to deal with this. >>> >>> Anyway, this means it is not enough to shift by 2 if the system hugepage >>> is more than 4k (e.g. 2M). I remember we had to change something due to >>> such hosts. virGetSystemPageSize(KB) should help with that. >>> >>> We could also make it 2^50 - pagesize just to make sure it will work for >>> a while, but some might not like it. >> >> I guess I'm not understanding how this code copes with the fact that >> we now have 3 different "unlimited" values to deal with. >> >> Could we not simply record the unlimited values and pick the right >> one based on kernel version we detect ? >> > > We have one, which we return for Get APIs that means that the setting > was not restricted. We would need to have a cgroup which we set to > some huge value and then read it, store it and compare it all the time. > It _should_ work as far as I can tell. No, I meant can we use some constants #define UNLIMTED_VALUE_KERNEL_A_B_C 2343243245325 #define UNLIMTED_VALUE_KERNEL_D_E_F 3253253253253253 #define UNLIMTED_VALUE_KERNEL_G_H_I 325325325325232 if kver == A_B_C && value == UNLIMTED_VALUE_KERNEL_A_B_C value = VIR_DOMAIN_MEMORY_PARAM_UNLIMITED else if kver == D_E_F && value == UNLIMTED_VALUE_KERNEL_D_E_F value = VIR_DOMAIN_MEMORY_PARAM_UNLIMITED else if kver == G_H_I && value == UNLIMTED_VALUE_KERNEL_G_H_I value = VIR_DOMAIN_MEMORY_PARAM_UNLIMITED Regards, Daniel