Re: [PATCH 6/7] containers (V7): BeanCounters over generic process containers

[Pavel Emelianov <xemul@sw.ru>]

Paul Menage wrote:
> On 2/13/07, Pavel Emelianov <xemul@sw.ru> wrote:
>>
>> I have implementation that moves arbitrary task :)
> 
> Is that the one that calls stop_machine() in order to move a task
> around? That seemed a little heavyweight ...

Nope :) I've rewritten it completely.

>> May be we can do context (container-on-task) handling lockless?
> 
> What did you have in mind?

The example patch is attached. Fits 2.6.20-rc6-mm3.

>> > I thought that we solved that problem by having a tmp_bc field in the
>> > task_struct that would take precedence over the main bc if it was
>> > non-null?
>>
>> Of course, but I'm commenting this patchset which doesn't have
>> this facility.
> 
> OK, I can add the concept in to the example too.
> 
> Paul
> 

--- ./kernel/bc/misc.c.bcctx	2007-01-31 13:56:45.000000000 +0300
+++ ./kernel/bc/misc.c	2007-01-31 14:20:32.000000000 +0300
@@ -0,0 +1,63 @@
+/*
+ * kernel/bc/misc.c
+ *
+ * Copyright (C) 2007 OpenVZ SWsoft Inc
+ *
+ */
+
+#include <linux/sched.h>
+#include <linux/stop_machine.h>
+#include <linux/module.h>
+
+#include <bc/beancounter.h>
+#include <bc/task.h>
+#include <bc/misc.h>
+
+static DEFINE_MUTEX(task_move_mutex);
+
+int copy_beancounter(struct task_struct *tsk, struct task_struct *parent)
+{
+	struct beancounter *bc;
+
+	bc = parent->exec_bc;
+	tsk->exec_bc = bc_get(bc);
+	BUG_ON(tsk->tmp_exec_bc != NULL);
+	return 0;
+}
+
+void free_beancounter(struct task_struct *tsk)
+{
+	struct beancounter *bc;
+
+	BUG_ON(tsk->tmp_exec_bc != NULL);
+	bc = tsk->exec_bc;
+	bc_put(bc);
+}
+
+int bc_task_move(int pid, struct beancounter *bc)
+{
+	struct task_struct *tsk;
+	struct beancounter *old_bc;
+
+	read_lock(&tasklist_lock);
+	tsk = find_task_by_pid(pid);
+	if (tsk)
+		get_task_struct(tsk);
+	read_unlock(&tasklist_lock);
+	if (tsk == NULL)
+		return -ESRCH;
+
+	mutex_lock(&task_move_mutex);
+	old_bc = tsk->exec_bc;
+
+	bc_get(bc);
+	rcu_assign_pointer(tsk->exec_bc, bc);
+
+	/* wait for all users if any get this beancounter */
+	synchronize_rcu();
+	mutex_unlock(&task_move_mutex);
+	bc_put(old_bc);
+
+	return err;
+}
+EXPORT_SYMBOL(bc_task_move);
--- ./kernel/fork.c.bcctx	2007-01-31 13:35:21.000000000 +0300
+++ ./kernel/fork.c	2007-01-31 13:56:45.000000000 +0300
@@ -51,6 +51,8 @@
 #include <linux/random.h>
 #include <linux/user_namespace.h>
 
+#include <bc/task.h>
+
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
 #include <asm/uaccess.h>
@@ -105,12 +107,18 @@ struct kmem_cache *vm_area_cachep;
 /* SLAB cache for mm_struct structures (tsk->mm) */
 static struct kmem_cache *mm_cachep;
 
-void free_task(struct task_struct *tsk)
+static void __free_task(struct task_struct *tsk)
 {
 	free_thread_info(tsk->thread_info);
 	rt_mutex_debug_task_free(tsk);
 	free_task_struct(tsk);
 }
+
+void free_task(struct task_struct *tsk)
+{
+	free_beancounter(tsk);
+	__free_task(tsk);
+}
 EXPORT_SYMBOL(free_task);
 
 void __put_task_struct(struct task_struct *tsk)
@@ -999,6 +1007,10 @@ static struct task_struct *copy_process(
 
 	rt_mutex_init_task(p);
 
+	retval = copy_beancounter(p, current);
+	if (retval < 0)
+		goto bad_fork_bc;
+
 #ifdef CONFIG_TRACE_IRQFLAGS
 	DEBUG_LOCKS_WARN_ON(!p->hardirqs_enabled);
 	DEBUG_LOCKS_WARN_ON(!p->softirqs_enabled);
@@ -1321,7 +1333,9 @@ bad_fork_cleanup_count:
 	atomic_dec(&p->user->processes);
 	free_uid(p->user);
 bad_fork_free:
-	free_task(p);
+	free_beancounter(p);
+bad_fork_bc:
+	__free_task(p);
 fork_out:
 	return ERR_PTR(retval);
 }
--- ./kernel/softirq.c.bcctx	2007-01-31 13:35:21.000000000 +0300
+++ ./kernel/softirq.c	2007-01-31 14:22:44.000000000 +0300
@@ -19,6 +19,8 @@
 #include <linux/smp.h>
 #include <linux/tick.h>
 
+#include <bc/task.h>
+
 #include <asm/irq.h>
 /*
    - No shared variables, all the data are CPU local.
@@ -210,6 +212,7 @@ asmlinkage void __do_softirq(void)
 	__u32 pending;
 	int max_restart = MAX_SOFTIRQ_RESTART;
 	int cpu;
+	struct beancounter *bc;
 
 	pending = local_softirq_pending();
 	account_system_vtime(current);
@@ -226,6 +229,7 @@ restart:
 
 	h = softirq_vec;
 
+	bc = set_exec_bc(&init_bc);
 	do {
 		if (pending & 1) {
 			h->action(h);
@@ -234,6 +238,7 @@ restart:
 		h++;
 		pending >>= 1;
 	} while (pending);
+	reset_exec_bc(bc, &init_bc);
 
 	local_irq_disable();
 
--- ./include/linux/sched.h.bcctx	2007-01-31 13:35:21.000000000 +0300
+++ ./include/linux/sched.h	2007-01-31 14:06:28.000000000 +0300
@@ -1082,6 +1082,10 @@ struct task_struct {
 #ifdef CONFIG_FAULT_INJECTION
 	int make_it_fail;
 #endif
+#ifdef CONFIG_BEANCOUNTERS
+	struct beancounter *exec_bc;
+	struct beancounter *tmp_exec_bc;
+#endif
 };
 
 static inline pid_t process_group(struct task_struct *tsk)
--- ./include/bc/task.h.bcctx	2007-01-31 13:56:45.000000000 +0300
+++ ./include/bc/task.h	2007-01-31 14:19:33.000000000 +0300
@@ -0,0 +1,68 @@
+/*
+ * include/bc/task.h
+ *
+ * Copyright (C) 2007 OpenVZ SWsoft Inc
+ *
+ */
+
+#ifndef __BC_TASK_H__
+#define __BC_TASK_H__
+
+struct beancounter;
+struct task_struct;
+
+#ifdef CONFIG_BEANCOUNTERS
+extern struct beancounter init_bc;
+
+/*
+ * Caller must be in rcu_read safe section
+ */
+static inline struct beancounter *get_exec_bc(void)
+{
+	struct task_struct *tsk;
+
+	if (in_irq())
+		return &init_bc;
+
+	tsk = current;
+	if (tsk->tmp_exec_bc != NULL)
+		return tsk->tmp_exec_bc;
+
+	return rcu_dereference(tsk->exec_bc);
+}
+
+#define set_exec_bc(bc)	({				\
+		struct task_struct *t;			\
+		struct beancounter *old;		\
+		t = current;				\
+		old = t->tmp_exec_bc;			\
+		t->tmp_exec_bc = bc;			\
+		old;					\
+	})
+
+#define reset_exec_bc(old, expected)	do {		\
+		struct task_struct *t;			\
+		t = current;				\
+		BUG_ON(t->tmp_exec_bc != expected);	\
+		t->tmp_exec_bc = old;			\
+	} while (0)
+
+int __must_check copy_beancounter(struct task_struct *tsk,
+		struct task_struct *parent);
+void free_beancounter(struct task_struct *tsk);
+int bc_task_move(int pid, struct beancounter *bc);
+#else
+static inline int __must_check copy_beancounter(struct task_struct *tsk,
+		struct task_struct *parent)
+{
+	return 0;
+}
+
+static inline void free_beancounter(struct task_struct *tsk)
+{
+}
+
+#define set_exec_bc(bc)		(NULL)
+#define reset_exec_bc(bc, exp)	do { } while (0)
+#endif
+#endif