[PATCH 4/8] memcg: add interface to migrate charge

[Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>]

This patch adds "memory.migrate_charge" file and handlers of it.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
---
 mm/memcontrol.c |   69 +++++++++++++++++++++++++++++++++++++++++++++++++++---
 1 files changed, 65 insertions(+), 4 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 6d77c80..6466e3c 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -225,6 +225,8 @@ struct mem_cgroup {
 	/* set when res.limit == memsw.limit */
 	bool		memsw_is_minimum;
 
+	unsigned int 	migrate_charge;
+
 	/*
 	 * statistics. This must be placed at the end of memcg.
 	 */
@@ -2826,6 +2828,31 @@ static int mem_cgroup_swappiness_write(struct cgroup *cgrp, struct cftype *cft,
 	return 0;
 }
 
+enum migrate_charge_type {
+	NR_MIGRATE_CHARGE_TYPE,
+};
+
+static u64 mem_cgroup_migrate_charge_read(struct cgroup *cgrp,
+					struct cftype *cft)
+{
+	return mem_cgroup_from_cont(cgrp)->migrate_charge;
+}
+
+static int mem_cgroup_migrate_charge_write(struct cgroup *cgrp,
+					struct cftype *cft, u64 val)
+{
+	struct mem_cgroup *mem = mem_cgroup_from_cont(cgrp);
+
+	if (val >= (1 << NR_MIGRATE_CHARGE_TYPE))
+		return -EINVAL;
+
+	cgroup_lock();
+	mem->migrate_charge = val;
+	cgroup_unlock();
+
+	return 0;
+}
+
 
 static struct cftype mem_cgroup_files[] = {
 	{
@@ -2875,6 +2902,11 @@ static struct cftype mem_cgroup_files[] = {
 		.read_u64 = mem_cgroup_swappiness_read,
 		.write_u64 = mem_cgroup_swappiness_write,
 	},
+	{
+		.name = "migrate_charge",
+		.read_u64 = mem_cgroup_migrate_charge_read,
+		.write_u64 = mem_cgroup_migrate_charge_write,
+	},
 };
 
 #ifdef CONFIG_CGROUP_MEM_RES_CTLR_SWAP
@@ -3115,6 +3147,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
 	if (parent)
 		mem->swappiness = get_swappiness(parent);
 	atomic_set(&mem->refcnt, 1);
+	mem->migrate_charge = 0;
 	return &mem->css;
 free_out:
 	__mem_cgroup_free(mem);
@@ -3151,6 +3184,35 @@ static int mem_cgroup_populate(struct cgroup_subsys *ss,
 	return ret;
 }
 
+static int mem_cgroup_can_migrate_charge(struct mem_cgroup *mem,
+					struct task_struct *p)
+{
+	return 0;
+}
+
+static int mem_cgroup_can_attach(struct cgroup_subsys *ss,
+				struct cgroup *cont,
+				struct task_struct *p,
+				bool threadgroup)
+{
+	struct mem_cgroup *mem = mem_cgroup_from_cont(cont);
+
+	if (mem->migrate_charge && thread_group_leader(p))
+		return mem_cgroup_can_migrate_charge(mem, p);
+	return 0;
+}
+
+static void mem_cgroup_cancel_attach(struct cgroup_subsys *ss,
+				struct cgroup *cont,
+				struct task_struct *p,
+				bool threadgroup)
+{
+}
+
+static void mem_cgroup_migrate_charge(void)
+{
+}
+
 static void mem_cgroup_move_task(struct cgroup_subsys *ss,
 				struct cgroup *cont,
 				struct cgroup *old_cont,
@@ -3158,10 +3220,7 @@ static void mem_cgroup_move_task(struct cgroup_subsys *ss,
 				bool threadgroup)
 {
 	mutex_lock(&memcg_tasklist);
-	/*
-	 * FIXME: It's better to move charges of this process from old
-	 * memcg to new memcg. But it's just on TODO-List now.
-	 */
+	mem_cgroup_migrate_charge();
 	mutex_unlock(&memcg_tasklist);
 }
 
@@ -3172,6 +3231,8 @@ struct cgroup_subsys mem_cgroup_subsys = {
 	.pre_destroy = mem_cgroup_pre_destroy,
 	.destroy = mem_cgroup_destroy,
 	.populate = mem_cgroup_populate,
+	.can_attach = mem_cgroup_can_attach,
+	.cancel_attach = mem_cgroup_cancel_attach,
 	.attach = mem_cgroup_move_task,
 	.early_init = 0,
 	.use_id = 1,

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