[libvirt] [PATCH v3] cgroup: Use system reported "unlimited" value for comparison

Viktor Mihajlovski mihajlov at linux.vnet.ibm.com
Wed Dec 7 08:13:48 UTC 2016

On 07.12.2016 07:51, Martin Kletzander wrote:
> On Tue, Dec 06, 2016 at 01:03:29PM +0100, 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.
>> This patch uses the value of memory.limit_in_bytes from the
>> cgroup memory root which is the system's "real" unlimited value
>> for comparison.
>> See also libvirt commit 231656bbeb9e4d3bedc44362784c35eee21cf0f4
>> for the history for kernel 3.12 and before.
>> Signed-off-by: Viktor Mihajlovski <mihajlov at linux.vnet.ibm.com> 
>> ---
>> v2: - removed RFC verbiage from commit message - per Martin's
>> review comment, cache the cgroup memory.limit_in_bytes - used the
>> cgroup detection logic proposed by Martin, much nicer now indeed 
>> - other than initially planned, fall back to 
>> VIR_DOMAIN_MEMORY_PARAM_UNLIMITED in case of cgroup read failure,
>> since the usual paranoia fits in nicely with the "already
>> initialized" check. With the current code structure this will 
>> never be called when the memory controller is not configured or
>> mounted anyway... - while at it, replaced the goto cleanups with
>> direct returns as there's really no cleanup to be done in the
>> GetMemoryxxxLimit functions
>> v3: - use thread safe one time initialization for the "unlimited"
>> value, to account for 64-bit architectures which do not guarantee
>> atomic memory updates of long long values (which reportedly is
>> the case for ARM).
> Perfect, ACK, pushed, thanks.
Great. Thanks!


Mit freundlichen Grüßen/Kind Regards
   Viktor Mihajlovski

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