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

[Martin Kletzander]

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.

Also some comment for the condition would be nice to have for others
reading the code in the future.

>> This patch deals with the rounding issue by scaling the byte values reported
>> by the kernel and the PARAM_UNLIMITED value to page size and comparing those.
>>
>> See also libvirt commit 231656bbeb9e4d3bedc44362784c35eee21cf0f4 for the
>> history for kernel 3.12 and before.
>>
>>
>
>ping ... it would be nice if this or an equivalent patch (comparison on
>4k boundaries) could be applied. Besides causing the goofy virsh memtune
>output, this breaks applications that compare current limits against
>VIR_DOMAIN_MEMORY_PARAM_UNLIMITED.
>
>Thanks!
>
>--
>
>Mit freundlichen Grüßen/Kind Regards
>   Viktor Mihajlovski
>
>IBM Deutschland Research & Development GmbH
>Vorsitzender des Aufsichtsrats: Martina Köderitz
>Geschäftsführung: Dirk Wittkopp
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>
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