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Date: Wed, 16 Jul 2014 11:46:16 +0200
From: Michal Hocko <mhocko@...e.cz>
To: Tejun Heo <tj@...nel.org>
Cc: lizefan@...wei.com, cgroups@...r.kernel.org,
linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
Vivek Goyal <vgoyal@...hat.com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Paul Mackerras <paulus@...ba.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Aristeu Rozanski <aris@...hat.com>,
"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Subject: Re: [PATCH 4/6] cgroup: distinguish the default and legacy
hierarchies when handling cftypes
On Mon 14-07-14 11:44:06, Tejun Heo wrote:
> Until now, cftype arrays carried files for both the default and legacy
> hierarchies and the files which needed to be used on only one of them
> were flagged with either CFTYPE_ONLY_ON_DFL or CFTYPE_INSANE. This
> gets confusing very quickly and we may end up exposing interface files
> to the default hierarchy without thinking it through.
>
> This patch makes cgroup core provide separate sets of interfaces for
> cftype handling so that the cftypes for the default and legacy
> hierarchies are clearly distinguished. The previous two patches
> renamed the existing ones so that they clearly indicate that they're
> for the legacy hierarchies. This patch adds the interface for the
> default hierarchy and apply them selectively depending on the
> hierarchy type.
>
> * cftypes added through cgroup_subsys->dfl_cftypes and
> cgroup_add_dfl_cftypes() only show up on the default hierarchy.
>
> * cftypes added through cgroup_subsys->legacy_cftypes and
> cgroup_add_legacy_cftypes() only show up on the legacy hierarchies.
>
> * cgroup_subsys->dfl_cftypes and ->legacy_cftypes can point to the
> same array for the cases where the interface files are identical on
> both types of hierarchies.
>
> * This makes all the existing subsystem interface files legacy-only by
> default and all subsystems will have no interface file created when
> enabled on the default hierarchy. Each subsystem should explicitly
> review and compose the interface for the default hierarchy.
>
> * A boot param "cgroup__DEVEL__legacy_files_on_dfl" is added which
> makes subsystems which haven't decided the interface files for the
> default hierarchy to present the legacy files on the default
> hierarchy so that its behavior on the default hierarchy can be
> tested. As the awkward name suggests, this is for development only.
>
> * memcg's CFTYPE_INSANE on "use_hierarchy" is noop now as the whole
> array isn't used on the default hierarchy. The flag is removed.
>
> v2: Updated documentation for cgroup__DEVEL__legacy_files_on_dfl.
>
> v3: Clear CFTYPE_ONLY_ON_DFL and CFTYPE_INSANE when cfts are removed
> as suggested by Li.
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Acked-by: Neil Horman <nhorman@...driver.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Michal Hocko <mhocko@...e.cz>
> Cc: Li Zefan <lizefan@...wei.com>
> Cc: Vivek Goyal <vgoyal@...hat.com>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: Aristeu Rozanski <aris@...hat.com>
> Cc: Aneesh Kumar K.V <aneesh.kumar@...ux.vnet.ibm.com>
As mentioned on the other email I will cook up a patch to allow basic
knobs for memcg.
Acked-by: Michal Hocko <mhocko@...e.cz>
> ---
> Documentation/cgroups/unified-hierarchy.txt | 18 ++++++---
> include/linux/cgroup.h | 9 ++++-
> kernel/cgroup.c | 62 +++++++++++++++++++++++++++--
> mm/memcontrol.c | 1 -
> 4 files changed, 78 insertions(+), 12 deletions(-)
>
> diff --git a/Documentation/cgroups/unified-hierarchy.txt b/Documentation/cgroups/unified-hierarchy.txt
> index a7a2205..4f45632 100644
> --- a/Documentation/cgroups/unified-hierarchy.txt
> +++ b/Documentation/cgroups/unified-hierarchy.txt
> @@ -94,12 +94,18 @@ change soon.
>
> mount -t cgroup -o __DEVEL__sane_behavior cgroup $MOUNT_POINT
>
> -All controllers which are not bound to other hierarchies are
> -automatically bound to unified hierarchy and show up at the root of
> -it. Controllers which are enabled only in the root of unified
> -hierarchy can be bound to other hierarchies. This allows mixing
> -unified hierarchy with the traditional multiple hierarchies in a fully
> -backward compatible way.
> +All controllers which support the unified hierarchy and are not bound
> +to other hierarchies are automatically bound to unified hierarchy and
> +show up at the root of it. Controllers which are enabled only in the
> +root of unified hierarchy can be bound to other hierarchies. This
> +allows mixing unified hierarchy with the traditional multiple
> +hierarchies in a fully backward compatible way.
> +
> +For development purposes, the following boot parameter makes all
> +controllers to appear on the unified hierarchy whether supported or
> +not.
> +
> + cgroup__DEVEL__legacy_files_on_dfl
>
> A controller can be moved across hierarchies only after the controller
> is no longer referenced in its current hierarchy. Because per-cgroup
> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
> index f5f0fee..9f76236 100644
> --- a/include/linux/cgroup.h
> +++ b/include/linux/cgroup.h
> @@ -590,6 +590,7 @@ static inline void pr_cont_cgroup_path(struct cgroup *cgrp)
>
> char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
>
> +int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
> int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
> int cgroup_rm_cftypes(struct cftype *cfts);
>
> @@ -671,8 +672,12 @@ struct cgroup_subsys {
> */
> struct list_head cfts;
>
> - /* base cftypes, automatically registered with subsys itself */
> - struct cftype *legacy_cftypes; /* used on the legacy hierarchies */
> + /*
> + * Base cftypes which are automatically registered. The two can
> + * point to the same array.
> + */
> + struct cftype *dfl_cftypes; /* for the default hierarchy */
> + struct cftype *legacy_cftypes; /* for the legacy hierarchies */
>
> /*
> * A subsystem may depend on other subsystems. When such subsystem
> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
> index c275aa4..374ebdf 100644
> --- a/kernel/cgroup.c
> +++ b/kernel/cgroup.c
> @@ -149,6 +149,12 @@ struct cgroup_root cgrp_dfl_root;
> */
> static bool cgrp_dfl_root_visible;
>
> +/*
> + * Set by the boot param of the same name and makes subsystems with NULL
> + * ->dfl_files to use ->legacy_files on the default hierarchy.
> + */
> +static bool cgroup_legacy_files_on_dfl;
> +
> /* some controllers are not supported in the default hierarchy */
> static const unsigned int cgrp_dfl_root_inhibit_ss_mask = 0
> #ifdef CONFIG_CGROUP_DEBUG
> @@ -3085,6 +3091,9 @@ static void cgroup_exit_cftypes(struct cftype *cfts)
> kfree(cft->kf_ops);
> cft->kf_ops = NULL;
> cft->ss = NULL;
> +
> + /* revert flags set by cgroup core while adding @cfts */
> + cft->flags &= ~(CFTYPE_ONLY_ON_DFL | CFTYPE_INSANE);
> }
> }
>
> @@ -3195,8 +3204,37 @@ static int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
> return ret;
> }
>
> +/**
> + * cgroup_add_dfl_cftypes - add an array of cftypes for default hierarchy
> + * @ss: target cgroup subsystem
> + * @cfts: zero-length name terminated array of cftypes
> + *
> + * Similar to cgroup_add_cftypes() but the added files are only used for
> + * the default hierarchy.
> + */
> +int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
> +{
> + struct cftype *cft;
> +
> + for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
> + cft->flags |= CFTYPE_ONLY_ON_DFL;
> + return cgroup_add_cftypes(ss, cfts);
> +}
> +
> +/**
> + * cgroup_add_legacy_cftypes - add an array of cftypes for legacy hierarchies
> + * @ss: target cgroup subsystem
> + * @cfts: zero-length name terminated array of cftypes
> + *
> + * Similar to cgroup_add_cftypes() but the added files are only used for
> + * the legacy hierarchies.
> + */
> int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts)
> {
> + struct cftype *cft;
> +
> + for (cft = cfts; cft && cft->name[0] != '\0'; cft++)
> + cft->flags |= CFTYPE_INSANE;
> return cgroup_add_cftypes(ss, cfts);
> }
>
> @@ -4893,9 +4931,19 @@ int __init cgroup_init(void)
> * disabled flag and cftype registration needs kmalloc,
> * both of which aren't available during early_init.
> */
> - if (!ss->disabled) {
> - cgrp_dfl_root.subsys_mask |= 1 << ss->id;
> - WARN_ON(cgroup_add_cftypes(ss, ss->legacy_cftypes));
> + if (ss->disabled)
> + continue;
> +
> + cgrp_dfl_root.subsys_mask |= 1 << ss->id;
> +
> + if (cgroup_legacy_files_on_dfl && !ss->dfl_cftypes)
> + ss->dfl_cftypes = ss->legacy_cftypes;
> +
> + if (ss->dfl_cftypes == ss->legacy_cftypes) {
> + WARN_ON(cgroup_add_cftypes(ss, ss->dfl_cftypes));
> + } else {
> + WARN_ON(cgroup_add_dfl_cftypes(ss, ss->dfl_cftypes));
> + WARN_ON(cgroup_add_legacy_cftypes(ss, ss->legacy_cftypes));
> }
> }
>
> @@ -5291,6 +5339,14 @@ static int __init cgroup_disable(char *str)
> }
> __setup("cgroup_disable=", cgroup_disable);
>
> +static int __init cgroup_set_legacy_files_on_dfl(char *str)
> +{
> + printk("cgroup: using legacy files on the default hierarchy\n");
> + cgroup_legacy_files_on_dfl = true;
> + return 0;
> +}
> +__setup("cgroup__DEVEL__legacy_files_on_dfl", cgroup_set_legacy_files_on_dfl);
> +
> /**
> * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
> * @dentry: directory dentry of interest
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index b6b3c6f..45c10c6 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -6003,7 +6003,6 @@ static struct cftype mem_cgroup_files[] = {
> },
> {
> .name = "use_hierarchy",
> - .flags = CFTYPE_INSANE,
> .write_u64 = mem_cgroup_hierarchy_write,
> .read_u64 = mem_cgroup_hierarchy_read,
> },
> --
> 1.9.3
>
--
Michal Hocko
SUSE Labs
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