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-rw-r--r--Documentation/admin-guide/cgroup-v2.rst8
-rw-r--r--include/linux/cgroup-defs.h19
-rw-r--r--init/Kconfig10
-rw-r--r--kernel/cgroup/cgroup-internal.h1
-rw-r--r--kernel/cgroup/cgroup-v1.c17
-rw-r--r--kernel/cgroup/cgroup.c43
6 files changed, 87 insertions, 11 deletions
diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index f0f03d5470b5..4bd0bee22a0d 100644
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -184,6 +184,14 @@ cgroup v2 currently supports the following mount options.
ignored on non-init namespace mounts. Please refer to the
Delegation section for details.
+ [no]favordynmods
+ Reduce the latencies of dynamic cgroup modifications such as
+ task migrations and controller on/offs at the cost of making
+ hot path operations such as forks and exits more expensive.
+ The static usage pattern of creating a cgroup, enabling
+ controllers, and then seeding it with CLONE_INTO_CGROUP is
+ not affected by this option.
+
memory_[no]localevents
Only populate memory.events with data for the current cgroup,
and not any subtrees. This is legacy behaviour, the default
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 672de25e3ec8..63bf43c7ca3b 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -89,19 +89,32 @@ enum {
CGRP_ROOT_NS_DELEGATE = (1 << 3),
/*
+ * Reduce latencies on dynamic cgroup modifications such as task
+ * migrations and controller on/offs by disabling percpu operation on
+ * cgroup_threadgroup_rwsem. This makes hot path operations such as
+ * forks and exits into the slow path and more expensive.
+ *
+ * The static usage pattern of creating a cgroup, enabling controllers,
+ * and then seeding it with CLONE_INTO_CGROUP doesn't require write
+ * locking cgroup_threadgroup_rwsem and thus doesn't benefit from
+ * favordynmod.
+ */
+ CGRP_ROOT_FAVOR_DYNMODS = (1 << 4),
+
+ /*
* Enable cpuset controller in v1 cgroup to use v2 behavior.
*/
- CGRP_ROOT_CPUSET_V2_MODE = (1 << 4),
+ CGRP_ROOT_CPUSET_V2_MODE = (1 << 16),
/*
* Enable legacy local memory.events.
*/
- CGRP_ROOT_MEMORY_LOCAL_EVENTS = (1 << 5),
+ CGRP_ROOT_MEMORY_LOCAL_EVENTS = (1 << 17),
/*
* Enable recursive subtree protection
*/
- CGRP_ROOT_MEMORY_RECURSIVE_PROT = (1 << 6),
+ CGRP_ROOT_MEMORY_RECURSIVE_PROT = (1 << 18),
};
/* cftype->flags */
diff --git a/init/Kconfig b/init/Kconfig
index c984afc489de..c93b10b3de3f 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -936,6 +936,16 @@ if CGROUPS
config PAGE_COUNTER
bool
+config CGROUP_FAVOR_DYNMODS
+ bool "Favor dynamic modification latency reduction by default"
+ help
+ This option enables the "favordynmods" mount option by default
+ which reduces the latencies of dynamic cgroup modifications such
+ as task migrations and controller on/offs at the cost of making
+ hot path operations such as forks and exits more expensive.
+
+ Say N if unsure.
+
config MEMCG
bool "Memory controller"
select PAGE_COUNTER
diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index 5da09c74228d..36b740cb3d59 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -233,6 +233,7 @@ void cgroup_kn_unlock(struct kernfs_node *kn);
int cgroup_path_ns_locked(struct cgroup *cgrp, char *buf, size_t buflen,
struct cgroup_namespace *ns);
+void cgroup_favor_dynmods(struct cgroup_root *root, bool favor);
void cgroup_free_root(struct cgroup_root *root);
void init_cgroup_root(struct cgroup_fs_context *ctx);
int cgroup_setup_root(struct cgroup_root *root, u16 ss_mask);
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index afc6c0e9c966..2ade21b54dc4 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -875,6 +875,8 @@ static int cgroup1_show_options(struct seq_file *seq, struct kernfs_root *kf_roo
seq_puts(seq, ",xattr");
if (root->flags & CGRP_ROOT_CPUSET_V2_MODE)
seq_puts(seq, ",cpuset_v2_mode");
+ if (root->flags & CGRP_ROOT_FAVOR_DYNMODS)
+ seq_puts(seq, ",favordynmods");
spin_lock(&release_agent_path_lock);
if (strlen(root->release_agent_path))
@@ -898,6 +900,8 @@ enum cgroup1_param {
Opt_noprefix,
Opt_release_agent,
Opt_xattr,
+ Opt_favordynmods,
+ Opt_nofavordynmods,
};
const struct fs_parameter_spec cgroup1_fs_parameters[] = {
@@ -909,6 +913,8 @@ const struct fs_parameter_spec cgroup1_fs_parameters[] = {
fsparam_flag ("noprefix", Opt_noprefix),
fsparam_string("release_agent", Opt_release_agent),
fsparam_flag ("xattr", Opt_xattr),
+ fsparam_flag ("favordynmods", Opt_favordynmods),
+ fsparam_flag ("nofavordynmods", Opt_nofavordynmods),
{}
};
@@ -960,6 +966,12 @@ int cgroup1_parse_param(struct fs_context *fc, struct fs_parameter *param)
case Opt_xattr:
ctx->flags |= CGRP_ROOT_XATTR;
break;
+ case Opt_favordynmods:
+ ctx->flags |= CGRP_ROOT_FAVOR_DYNMODS;
+ break;
+ case Opt_nofavordynmods:
+ ctx->flags &= ~CGRP_ROOT_FAVOR_DYNMODS;
+ break;
case Opt_release_agent:
/* Specifying two release agents is forbidden */
if (ctx->release_agent)
@@ -1211,8 +1223,11 @@ static int cgroup1_root_to_use(struct fs_context *fc)
init_cgroup_root(ctx);
ret = cgroup_setup_root(root, ctx->subsys_mask);
- if (ret)
+ if (!ret)
+ cgroup_favor_dynmods(root, ctx->flags & CGRP_ROOT_FAVOR_DYNMODS);
+ else
cgroup_free_root(root);
+
return ret;
}
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 9ce24d5cf2d5..7d023d42a6a5 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1305,6 +1305,20 @@ struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root)
return root_cgrp->root;
}
+void cgroup_favor_dynmods(struct cgroup_root *root, bool favor)
+{
+ bool favoring = root->flags & CGRP_ROOT_FAVOR_DYNMODS;
+
+ /* see the comment above CGRP_ROOT_FAVOR_DYNMODS definition */
+ if (favor && !favoring) {
+ rcu_sync_enter(&cgroup_threadgroup_rwsem.rss);
+ root->flags |= CGRP_ROOT_FAVOR_DYNMODS;
+ } else if (!favor && favoring) {
+ rcu_sync_exit(&cgroup_threadgroup_rwsem.rss);
+ root->flags &= ~CGRP_ROOT_FAVOR_DYNMODS;
+ }
+}
+
static int cgroup_init_root_id(struct cgroup_root *root)
{
int id;
@@ -1365,6 +1379,7 @@ static void cgroup_destroy_root(struct cgroup_root *root)
cgroup_root_count--;
}
+ cgroup_favor_dynmods(root, false);
cgroup_exit_root_id(root);
mutex_unlock(&cgroup_mutex);
@@ -1858,6 +1873,7 @@ int cgroup_show_path(struct seq_file *sf, struct kernfs_node *kf_node,
enum cgroup2_param {
Opt_nsdelegate, Opt_nonsdelegate,
+ Opt_favordynmods, Opt_nofavordynmods,
Opt_memory_localevents, Opt_memory_nolocalevents,
Opt_memory_recursiveprot, Opt_memory_norecursiveprot,
nr__cgroup2_params
@@ -1866,6 +1882,8 @@ enum cgroup2_param {
static const struct fs_parameter_spec cgroup2_fs_parameters[] = {
fsparam_flag("nsdelegate", Opt_nsdelegate),
fsparam_flag("nonsdelegate", Opt_nonsdelegate),
+ fsparam_flag("favordynmods", Opt_favordynmods),
+ fsparam_flag("nofavordynmods", Opt_nofavordynmods),
fsparam_flag("memory_localevents", Opt_memory_localevents),
fsparam_flag("memory_nolocalevents", Opt_memory_nolocalevents),
fsparam_flag("memory_recursiveprot", Opt_memory_recursiveprot),
@@ -1890,6 +1908,12 @@ static int cgroup2_parse_param(struct fs_context *fc, struct fs_parameter *param
case Opt_nonsdelegate:
ctx->flags &= ~CGRP_ROOT_NS_DELEGATE;
return 0;
+ case Opt_favordynmods:
+ ctx->flags |= CGRP_ROOT_FAVOR_DYNMODS;
+ return 0;
+ case Opt_nofavordynmods:
+ ctx->flags &= ~CGRP_ROOT_FAVOR_DYNMODS;
+ return 0;
case Opt_memory_localevents:
ctx->flags |= CGRP_ROOT_MEMORY_LOCAL_EVENTS;
return 0;
@@ -1914,6 +1938,9 @@ static void apply_cgroup_root_flags(unsigned int root_flags)
else
cgrp_dfl_root.flags &= ~CGRP_ROOT_NS_DELEGATE;
+ cgroup_favor_dynmods(&cgrp_dfl_root,
+ root_flags & CGRP_ROOT_FAVOR_DYNMODS);
+
if (root_flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS)
cgrp_dfl_root.flags |= CGRP_ROOT_MEMORY_LOCAL_EVENTS;
else
@@ -1930,6 +1957,8 @@ static int cgroup_show_options(struct seq_file *seq, struct kernfs_root *kf_root
{
if (cgrp_dfl_root.flags & CGRP_ROOT_NS_DELEGATE)
seq_puts(seq, ",nsdelegate");
+ if (cgrp_dfl_root.flags & CGRP_ROOT_FAVOR_DYNMODS)
+ seq_puts(seq, ",favordynmods");
if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_LOCAL_EVENTS)
seq_puts(seq, ",memory_localevents");
if (cgrp_dfl_root.flags & CGRP_ROOT_MEMORY_RECURSIVE_PROT)
@@ -1980,7 +2009,8 @@ void init_cgroup_root(struct cgroup_fs_context *ctx)
cgrp->root = root;
init_cgroup_housekeeping(cgrp);
- root->flags = ctx->flags;
+ /* DYNMODS must be modified through cgroup_favor_dynmods() */
+ root->flags = ctx->flags & ~CGRP_ROOT_FAVOR_DYNMODS;
if (ctx->release_agent)
strscpy(root->release_agent_path, ctx->release_agent, PATH_MAX);
if (ctx->name)
@@ -2202,6 +2232,10 @@ static int cgroup_init_fs_context(struct fs_context *fc)
put_user_ns(fc->user_ns);
fc->user_ns = get_user_ns(ctx->ns->user_ns);
fc->global = true;
+
+#ifdef CONFIG_CGROUP_FAVOR_DYNMODS
+ ctx->flags |= CGRP_ROOT_FAVOR_DYNMODS;
+#endif
return 0;
}
@@ -5854,12 +5888,6 @@ int __init cgroup_init(void)
cgroup_rstat_boot();
- /*
- * The latency of the synchronize_rcu() is too high for cgroups,
- * avoid it at the cost of forcing all readers into the slow path.
- */
- rcu_sync_enter_start(&cgroup_threadgroup_rwsem.rss);
-
get_user_ns(init_cgroup_ns.user_ns);
mutex_lock(&cgroup_mutex);
@@ -6771,6 +6799,7 @@ static ssize_t features_show(struct kobject *kobj, struct kobj_attribute *attr,
{
return snprintf(buf, PAGE_SIZE,
"nsdelegate\n"
+ "favordynmods\n"
"memory_localevents\n"
"memory_recursiveprot\n");
}
generated by cgit v1.2.3-58-ga151 (git 2.39.0) at 2024-12-03 08:37:47 +0000