Re: [PATCH] Documentation/memcg: update memcg/kmem status

Michal Hocko
2015-04-07T15:14:03Z

On Wed 01-04-15 17:30:36, Vladimir Davydov wrote:
> Memcg/kmem reclaim support has been finally merged. Reflect this in the
> documentation.
>
> Signed-off-by: Vladimir Davydov <vdavydov@parallels.com>

Acked-by: Michal Hocko <mhocko@suse.cz>

> ---
> Documentation/cgroups/memory.txt | 8 +++-----
> init/Kconfig | 6 ------
> 2 files changed, 3 insertions(+), 11 deletions(-)
>
> diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt
> index a22df3ad35ff..f456b4315e86 100644
> --- a/Documentation/cgroups/memory.txt
> +++ b/Documentation/cgroups/memory.txt
> @@ -275,11 +275,6 @@ When oom event notifier is registered, event will be delivered.
>
> 2.7 Kernel Memory Extension (CONFIG_MEMCG_KMEM)
>
> -WARNING: Current implementation lacks reclaim support. That means allocation
> - attempts will fail when close to the limit even if there are plenty of
> - kmem available for reclaim. That makes this option unusable in real
> - life so DO NOT SELECT IT unless for development purposes.
> -
> With the Kernel memory extension, the Memory Controller is able to limit
> the amount of kernel memory used by the system. Kernel memory is fundamentally
> different than user memory, since it can't be swapped out, which makes it
> @@ -345,6 +340,9 @@ set:
> In this case, the admin could set up K so that the sum of all groups is
> never greater than the total memory, and freely set U at the cost of his
> QoS.
> + WARNING: In the current implementation, memory reclaim will NOT be
> + triggered for a cgroup when it hits K while staying below U, which makes
> + this setup impractical.
>
> U != 0, K >= U:
> Since kmem charges will also be fed to the user counter and reclaim will be
> diff --git a/init/Kconfig b/init/Kconfig
> index 7766b500f679..caffca37ccb7 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1059,12 +1059,6 @@ config MEMCG_KMEM
> the kmem extension can use it to guarantee that no group of processes
> will ever exhaust kernel resources alone.
>
> - WARNING: Current implementation lacks reclaim support. That means
> - allocation attempts will fail when close to the limit even if there
> - are plenty of kmem available for reclaim. That makes this option
> - unusable in real life so DO NOT SELECT IT unless for development
> - purposes.
> -
> config CGROUP_HUGETLB
> bool "HugeTLB Resource Controller for Control Groups"
> depends on HUGETLB_PAGE
> --
> 1.7.10.4
>
> --
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--
Michal Hocko
SUSE Labs