linux-kernel - Re: [PATCH -V8 16/16] hugetlb/cgroup: add HugeTLB controller documentation

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Date:	Tue, 12 Jun 2012 17:57:54 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
CC:	linux-mm@...ck.org, dhillf@...il.com, rientjes@...gle.com,
	mhocko@...e.cz, akpm@...ux-foundation.org, hannes@...xchg.org,
	linux-kernel@...r.kernel.org, cgroups@...r.kernel.org
Subject: Re: [PATCH -V8 16/16] hugetlb/cgroup: add HugeTLB controller documentation

(2012/06/09 18:00), Aneesh Kumar K.V wrote:
> From: "Aneesh Kumar K.V"<aneesh.kumar@...ux.vnet.ibm.com>
> 
> Signed-off-by: Aneesh Kumar K.V<aneesh.kumar@...ux.vnet.ibm.com>

Documentation in patch 1/16 will help other guy's review.


> ---
>   Documentation/cgroups/hugetlb.txt |   45 +++++++++++++++++++++++++++++++++++++
>   1 file changed, 45 insertions(+)
>   create mode 100644 Documentation/cgroups/hugetlb.txt
> 
> diff --git a/Documentation/cgroups/hugetlb.txt b/Documentation/cgroups/hugetlb.txt
> new file mode 100644
> index 0000000..a9faaca
> --- /dev/null
> +++ b/Documentation/cgroups/hugetlb.txt
> @@ -0,0 +1,45 @@
> +HugeTLB Controller
> +-------------------
> +
> +The HugeTLB controller allows to limit the HugeTLB usage per control group and
> +enforces the controller limit during page fault. Since HugeTLB doesn't
> +support page reclaim, enforcing the limit at page fault time implies that,
> +the application will get SIGBUS signal if it tries to access HugeTLB pages
> +beyond its limit. This requires the application to know beforehand how much
> +HugeTLB pages it would require for its use.
> +


Isn't it better to mention hugetlb cgroup doesn't have its own free-huge-page-list,
it's just a quota. And system admin need to set up hugetlb page pool regardless
of using hugetlb cgroup.


> +HugeTLB controller can be created by first mounting the cgroup filesystem.
> +
> +# mount -t cgroup -o hugetlb none /sys/fs/cgroup
> +
> +With the above step, the initial or the parent HugeTLB group becomes
> +visible at /sys/fs/cgroup. At bootup, this group includes all the tasks in
> +the system. /sys/fs/cgroup/tasks lists the tasks in this cgroup.
> +
> +New groups can be created under the parent group /sys/fs/cgroup.
> +
> +# cd /sys/fs/cgroup
> +# mkdir g1
> +# echo $$>  g1/tasks
> +
> +The above steps create a new group g1 and move the current shell
> +process (bash) into it.
> +
> +Brief summary of control files
> +
> + hugetlb.<hugepagesize>.limit_in_bytes     # set/show limit of "hugepagesize" hugetlb usage
> + hugetlb.<hugepagesize>.max_usage_in_bytes # show max "hugepagesize" hugetlb  usage recorded
> + hugetlb.<hugepagesize>.usage_in_bytes     # show current res_counter usage for "hugepagesize" hugetlb
> + hugetlb.<hugepagesize>.failcnt		   # show the number of allocation failure due to HugeTLB limit
                                         ^^^^^^^^
breakage in spacing.

> +
> +For a system supporting two hugepage size (16M and 16G) the control
> +files include:
> +
> +hugetlb.16GB.limit_in_bytes
> +hugetlb.16GB.max_usage_in_bytes
> +hugetlb.16GB.usage_in_bytes
> +hugetlb.16GB.failcnt
> +hugetlb.16MB.limit_in_bytes
> +hugetlb.16MB.max_usage_in_bytes
> +hugetlb.16MB.usage_in_bytes
> +hugetlb.16MB.failcnt

seems nice.

Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

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