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231656bbeb
Since kernel 3.12 (commit 34ff8dc08956098563989d8599840b130be81252 in linux-stable.git in particular) the value for 'unlimited' in cgroup memory limits changed from LLONG_MAX to ULLONG_MAX. Due to rather unfortunate choice of our VIR_DOMAIN_MEMORY_PARAM_UNLIMITED constant (which we transfer as an unsigned long long in Kibibytes), we ended up with the situation described below (applies to x86_64): - 2^64-1 (ULLONG_MAX) -- "unlimited" in kernel = 3.12 - 2^63-1 (LLONG_MAX) -- "unlimited" in kernel < 3.12 - 2^63-1024 -- our PARAM_UNLIMITED scaled to Bytes - 2^53-1 -- our PARAM_UNLIMITED unscaled (in Kibibytes) This means that when any number within (2^63-1, 2^64-1] is read from memory cgroup, we are transferring that number instead of "unlimited". Unfortunately, changing VIR_DOMAIN_MEMORY_PARAM_UNLIMITED would break ABI compatibility and thus we have to resort to a different solution. With this patch every value greater than PARAM_UNLIMITED means "unlimited". Even though this may seem misleading, we are already in such unclear situation when running 3.12 kernel with memory limits set to 2^63. One example showing most of the problems at once (with kernel 3.12.2): # virsh memtune asdf --hard-limit 9007199254740991 --swap-hard-limit -1 # echo 12345678901234567890 >\ /sys/fs/cgroup/memory/machine/asdf.libvirt-qemu/memory.soft_limit_in_bytes # virsh memtune asdf hard_limit : 18014398509481983 soft_limit : 12056327051986884 swap_hard_limit: 18014398509481983 Signed-off-by: Martin Kletzander <mkletzan@redhat.com>
LibVirt : simple API for virtualization
Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.
Daniel Veillard <veillard@redhat.com>