Re: [PATCH] Memory Resource Controller Add Boot Option

[Paul Menage <menage@google.com>]

>> I'll send out a prototype for comment.

Something like the patch below. The effects of cgroup_disable=foo are:

- foo doesn't show up in /proc/cgroups
- foo isn't auto-mounted if you mount all cgroups in a single hierarchy
- foo isn't visible as an individually mountable subsystem

As a result there will only ever be one call to foo->create(), at init time; all processes will stay in this group, and the group will never be mounted on a visible hierarchy. Any additional effects (e.g. not allocating metadata) are up to the foo subsystem.

This doesn't handle early_init subsystems (their "disabled" bit isn't set be, but it could easily be extended to do so if any of the early_init systems wanted it - I think it would just involve some nastier parameter processing since it would occur before the command-line argument parser had been run.

 include/linux/cgroup.h |    1 +
 kernel/cgroup.c        |   29 +++++++++++++++++++++++++++--
 2 files changed, 28 insertions(+), 2 deletions(-)

Index: cgroup_disable-2.6.25-rc2-mm1/include/linux/cgroup.h
===================================================================
--- cgroup_disable-2.6.25-rc2-mm1.orig/include/linux/cgroup.h
+++ cgroup_disable-2.6.25-rc2-mm1/include/linux/cgroup.h
@@ -256,6 +256,7 @@ struct cgroup_subsys {
 	void (*bind)(struct cgroup_subsys *ss, struct cgroup *root);
 	int subsys_id;
 	int active;
+	int disabled;
 	int early_init;
 #define MAX_CGROUP_TYPE_NAMELEN 32
 	const char *name;
Index: cgroup_disable-2.6.25-rc2-mm1/kernel/cgroup.c
===================================================================
--- cgroup_disable-2.6.25-rc2-mm1.orig/kernel/cgroup.c
+++ cgroup_disable-2.6.25-rc2-mm1/kernel/cgroup.c
@@ -790,7 +790,14 @@ static int parse_cgroupfs_options(char *
 		if (!*token)
 			return -EINVAL;
 		if (!strcmp(token, "all")) {
-			opts->subsys_bits = (1 << CGROUP_SUBSYS_COUNT) - 1;
+			/* Add all non-disabled subsystems */
+			int i;
+			opts->subsys_bits = 0;
+			for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+				struct cgroup_subsys *ss = subsys[i];
+				if (!ss->disabled)
+					opts->subsys_bits |= 1ul << i;
+			}
 		} else if (!strcmp(token, "noprefix")) {
 			set_bit(ROOT_NOPREFIX, &opts->flags);
 		} else if (!strncmp(token, "release_agent=", 14)) {
@@ -808,7 +815,8 @@ static int parse_cgroupfs_options(char *
 			for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
 				ss = subsys[i];
 				if (!strcmp(token, ss->name)) {
-					set_bit(i, &opts->subsys_bits);
+					if (!ss->disabled)
+						set_bit(i, &opts->subsys_bits);
 					break;
 				}
 			}
@@ -2596,6 +2606,8 @@ static int proc_cgroupstats_show(struct 
 	mutex_lock(&cgroup_mutex);
 	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
 		struct cgroup_subsys *ss = subsys[i];
+		if (ss->disabled)
+			continue;
 		seq_printf(m, "%s\t%lu\t%d\n",
 			   ss->name, ss->root->subsys_bits,
 			   ss->root->number_of_cgroups);
@@ -2991,3 +3003,16 @@ static void cgroup_release_agent(struct 
 	spin_unlock(&release_list_lock);
 	mutex_unlock(&cgroup_mutex);
 }
+
+static int __init cgroup_disable(char *str)
+{
+	int i;
+	for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+		struct cgroup_subsys *ss = subsys[i];
+		if (!strcmp(str, ss->name)) {
+			ss->disabled = 1;
+			break;
+		}
+	}
+}
+__setup("cgroup_disable=", cgroup_disable);


> 
> Sure thing, if css has the flag, then it would nice. Could you wrap it up to say
> something like css_disabled(&mem_cgroup_subsys)
> 
> 

It's the subsys object rather than the css (cgroup_subsys_state).

  We could have something like:

#define cgroup_subsys_disabled(_ss) ((ss_)->disabled)

but I don't see that 

  cgroup_subsys_disabled(&mem_cgroup_subsys) 

is better than just putting

  mem_cgroup_subsys.disabled

Paul