Message-ID: <48036677.3010807@linux.vnet.ibm.com>
Date:	Mon, 14 Apr 2008 19:43:11 +0530
From:	Balbir Singh <balbir@...ux.vnet.ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Paul Menage <menage@...gle.com>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: [Fwd: [-mm] Add an owner to the mm_struct (v9)]

Hi,

If nobody has any specific objection to this patch, can I go ahead and request
Andrew to include this patch?

Balbir


-------- Original Message --------
Subject: [-mm] Add an owner to the mm_struct (v9)
Date: Thu, 10 Apr 2008 14:46:02 +0530
From: Balbir Singh <balbir@...ux.vnet.ibm.com>
To: Paul Menage <menage@...gle.com>, Pavel Emelianov <xemul@...nvz.org>
CC: Hugh Dickins <hugh@...itas.com>, Sudhir Kumar <skumar@...ux.vnet.ibm.com>,
YAMAMOTO Takashi <yamamoto@...inux.co.jp>, linux-kernel@...r.kernel.org,
taka@...inux.co.jp, linux-mm@...ck.org, David Rientjes <rientjes@...gle.com>,
Balbir Singh <balbir@...ux.vnet.ibm.com>,        Andrew Morton
<akpm@...ux-foundation.org>,        KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com>


Changelog v8
------------
1. CONFIG_MM_OWNER has no help, it is an internal option to be used by
   other configuration controls.
2. Added __read_mostly for cgroup_mm_owner_callback
3. Removed delay_group_leader() optimization

Changelog v7
------------
1. Make mm_need_new_owner() more readable
2. Remove extra white space from init_task.h

Changelog v6
------------

1. Fix typos
2. Document the use of delay_group_leader()

Changelog v5
------------
Remove the hooks for .owner from init_task.h and move it to init/main.c

Changelog v4
------------
1. Release rcu_read_lock() after acquiring task_lock(). Also get a reference
   to the task_struct
2. Change cgroup mm_owner_changed callback to callback only if the
   cgroup of old and new task is different and to pass the old and new
   cgroups instead of task pointers
3. Port the patch to 2.6.25-rc8-mm1

Changelog v3
------------

1. Add mm->owner change callbacks using cgroups

This patch removes the mem_cgroup member from mm_struct and instead adds
an owner. This approach was suggested by Paul Menage. The advantage of
this approach is that, once the mm->owner is known, using the subsystem
id, the cgroup can be determined. It also allows several control groups
that are virtually grouped by mm_struct, to exist independent of the memory
controller i.e., without adding mem_cgroup's for each controller,
to mm_struct.

A new config option CONFIG_MM_OWNER is added and the memory resource
controller selects this config option.

This patch also adds cgroup callbacks to notify subsystems when mm->owner
changes. The mm_cgroup_changed callback is called with the task_lock()
of the new task held and is called just prior to changing the mm->owner.

I am indebted to Paul Menage for the several reviews of this patchset
and helping me make it lighter and simpler.

This patch was tested on a powerpc box, it was compiled with both the
MM_OWNER config turned on and off.

After the thread group leader exits, it's moved to init_css_state by
cgroup_exit(), thus all future charges from runnings threads would
be redirected to the init_css_set's subsystem.

Signed-off-by: Balbir Singh <balbir@...ux.vnet.ibm.com>
---

 fs/exec.c                  |    1
 include/linux/cgroup.h     |   15 ++++++++
 include/linux/memcontrol.h |   16 +-------
 include/linux/mm_types.h   |    5 +-
 include/linux/sched.h      |   13 +++++++
 init/Kconfig               |    7 +++
 init/main.c                |    1
 kernel/cgroup.c            |   30 ++++++++++++++++
 kernel/exit.c              |   83 +++++++++++++++++++++++++++++++++++++++++++++
 kernel/fork.c              |   11 ++++-
 mm/memcontrol.c            |   24 +------------
 11 files changed, 167 insertions(+), 39 deletions(-)

diff -puN fs/exec.c~memory-controller-add-mm-owner fs/exec.c
--- linux-2.6.25-rc8/fs/exec.c~memory-controller-add-mm-owner	2008-04-08
17:23:20.000000000 +0530
+++ linux-2.6.25-rc8-balbir/fs/exec.c	2008-04-08 17:23:20.000000000 +0530
@@ -735,6 +735,7 @@ static int exec_mmap(struct mm_struct *m
 	tsk->active_mm = mm;
 	activate_mm(active_mm, mm);
 	task_unlock(tsk);
+	mm_update_next_owner(mm);
 	arch_pick_mmap_layout(mm);
 	if (old_mm) {
 		up_read(&old_mm->mmap_sem);
diff -puN include/linux/cgroup.h~memory-controller-add-mm-owner
include/linux/cgroup.h
--- linux-2.6.25-rc8/include/linux/cgroup.h~memory-controller-add-mm-owner
2008-04-08 17:23:20.000000000 +0530
+++ linux-2.6.25-rc8-balbir/include/linux/cgroup.h	2008-04-08 17:23:20.000000000
+0530
@@ -300,6 +300,12 @@ struct cgroup_subsys {
 			struct cgroup *cgrp);
 	void (*post_clone)(struct cgroup_subsys *ss, struct cgroup *cgrp);
 	void (*bind)(struct cgroup_subsys *ss, struct cgroup *root);
+	/*
+	 * This routine is called with the task_lock of mm->owner held
+	 */
+	void (*mm_owner_changed)(struct cgroup_subsys *ss,
+					struct cgroup *old,
+					struct cgroup *new);
 	int subsys_id;
 	int active;
 	int disabled;
@@ -385,4 +391,13 @@ static inline int cgroupstats_build(stru

 #endif /* !CONFIG_CGROUPS */

+#ifdef CONFIG_MM_OWNER
+extern void
+cgroup_mm_owner_callbacks(struct task_struct *old, struct task_struct *new);
+#else /* !CONFIG_MM_OWNER */
+static inline void
+cgroup_mm_owner_callbacks(struct task_struct *old, struct task_struct *new)
+{
+}
+#endif /* CONFIG_MM_OWNER */
 #endif /* _LINUX_CGROUP_H */
diff -puN include/linux/init_task.h~memory-controller-add-mm-owner
include/linux/init_task.h
diff -puN include/linux/memcontrol.h~memory-controller-add-mm-owner
include/linux/memcontrol.h
--- linux-2.6.25-rc8/include/linux/memcontrol.h~memory-controller-add-mm-owner
2008-04-08 17:23:20.000000000 +0530
+++ linux-2.6.25-rc8-balbir/include/linux/memcontrol.h	2008-04-08
17:23:20.000000000 +0530
@@ -27,9 +27,6 @@ struct mm_struct;

 #ifdef CONFIG_CGROUP_MEM_RES_CTLR

-extern void mm_init_cgroup(struct mm_struct *mm, struct task_struct *p);
-extern void mm_free_cgroup(struct mm_struct *mm);
-
 #define page_reset_bad_cgroup(page)	((page)->page_cgroup = 0)

 extern struct page_cgroup *page_get_page_cgroup(struct page *page);
@@ -48,8 +45,10 @@ extern unsigned long mem_cgroup_isolate_
 extern void mem_cgroup_out_of_memory(struct mem_cgroup *mem, gfp_t gfp_mask);
 int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem);

+extern struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
+
 #define mm_match_cgroup(mm, cgroup)	\
-	((cgroup) == rcu_dereference((mm)->mem_cgroup))
+	((cgroup) == mem_cgroup_from_task((mm)->owner))

 extern int mem_cgroup_prepare_migration(struct page *page);
 extern void mem_cgroup_end_migration(struct page *page);
@@ -73,15 +72,6 @@ extern long mem_cgroup_calc_reclaim_inac
 				struct zone *zone, int priority);

 #else /* CONFIG_CGROUP_MEM_RES_CTLR */
-static inline void mm_init_cgroup(struct mm_struct *mm,
-					struct task_struct *p)
-{
-}
-
-static inline void mm_free_cgroup(struct mm_struct *mm)
-{
-}
-
 static inline void page_reset_bad_cgroup(struct page *page)
 {
 }
diff -puN include/linux/mm_types.h~memory-controller-add-mm-owner
include/linux/mm_types.h
--- linux-2.6.25-rc8/include/linux/mm_types.h~memory-controller-add-mm-owner
2008-04-08 17:23:20.000000000 +0530
+++ linux-2.6.25-rc8-balbir/include/linux/mm_types.h	2008-04-08
17:23:20.000000000 +0530
@@ -230,8 +230,9 @@ struct mm_struct {
 	/* aio bits */
 	rwlock_t		ioctx_list_lock;	/* aio lock */
 	struct kioctx		*ioctx_list;
-#ifdef CONFIG_CGROUP_MEM_RES_CTLR
-	struct mem_cgroup *mem_cgroup;
+#ifdef CONFIG_MM_OWNER
+	struct task_struct *owner;	/* The thread group leader that */
+					/* owns the mm_struct.		*/
 #endif

 #ifdef CONFIG_PROC_FS
diff -puN include/linux/sched.h~memory-controller-add-mm-owner include/linux/sched.h
--- linux-2.6.25-rc8/include/linux/sched.h~memory-controller-add-mm-owner
2008-04-08 17:23:20.000000000 +0530
+++ linux-2.6.25-rc8-balbir/include/linux/sched.h	2008-04-08 17:23:20.000000000
+0530
@@ -2144,6 +2144,19 @@ static inline void migration_init(void)

 #define TASK_STATE_TO_CHAR_STR "RSDTtZX"

+#ifdef CONFIG_MM_OWNER
+extern void mm_update_next_owner(struct mm_struct *mm);
+extern void mm_init_owner(struct mm_struct *mm, struct task_struct *p);
+#else
+static inline void mm_update_next_owner(struct mm_struct *mm)
+{
+}
+
+static inline void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
+{
+}
+#endif /* CONFIG_MM_OWNER */
+
 #endif /* __KERNEL__ */

 #endif
diff -puN init/Kconfig~memory-controller-add-mm-owner init/Kconfig
--- linux-2.6.25-rc8/init/Kconfig~memory-controller-add-mm-owner	2008-04-08
17:23:20.000000000 +0530
+++ linux-2.6.25-rc8-balbir/init/Kconfig	2008-04-08 17:31:38.000000000 +0530
@@ -371,9 +371,13 @@ config RESOURCE_COUNTERS
           infrastructure that works with cgroups
 	depends on CGROUPS

+config MM_OWNER
+	bool
+
 config CGROUP_MEM_RES_CTLR
 	bool "Memory Resource Controller for Control Groups"
 	depends on CGROUPS && RESOURCE_COUNTERS
+	select MM_OWNER
 	help
 	  Provides a memory resource controller that manages both page cache and
 	  RSS memory.
@@ -386,6 +390,9 @@ config CGROUP_MEM_RES_CTLR
 	  Only enable when you're ok with these trade offs and really
 	  sure you need the memory resource controller.

+	  This config option also selects MM_OWNER config option, which
+	  could in turn add some fork/exit overhead.
+
 config SYSFS_DEPRECATED
 	bool

diff -puN kernel/cgroup.c~memory-controller-add-mm-owner kernel/cgroup.c
--- linux-2.6.25-rc8/kernel/cgroup.c~memory-controller-add-mm-owner	2008-04-08
17:23:20.000000000 +0530
+++ linux-2.6.25-rc8-balbir/kernel/cgroup.c	2008-04-08 17:29:45.000000000 +0530
@@ -118,6 +118,7 @@ static int root_count;
  * be called.
  */
 static int need_forkexit_callback;
+static int need_mm_owner_callback __read_mostly;

 /* convenient tests for these bits */
 inline int cgroup_is_removed(const struct cgroup *cgrp)
@@ -2485,6 +2486,7 @@ static void __init cgroup_init_subsys(st
 	}

 	need_forkexit_callback |= ss->fork || ss->exit;
+	need_mm_owner_callback |= !!ss->mm_owner_changed;

 	ss->active = 1;
 }
@@ -2721,6 +2723,34 @@ void cgroup_fork_callbacks(struct task_s
 	}
 }

+#ifdef CONFIG_MM_OWNER
+/**
+ * cgroup_mm_owner_callbacks - run callbacks when the mm->owner changes
+ * @p: the new owner
+ *
+ * Called on every change to mm->owner. mm_init_owner() does not
+ * invoke this routine, since it assigns the mm->owner the first time
+ * and does not change it.
+ */
+void cgroup_mm_owner_callbacks(struct task_struct *old, struct task_struct *new)
+{
+	struct cgroup *oldcgrp, *newcgrp;
+
+	if (need_mm_owner_callback) {
+		int i;
+		for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+			struct cgroup_subsys *ss = subsys[i];
+			oldcgrp = task_cgroup(old, ss->subsys_id);
+			newcgrp = task_cgroup(new, ss->subsys_id);
+			if (oldcgrp == newcgrp)
+				continue;
+			if (ss->mm_owner_changed)
+				ss->mm_owner_changed(ss, oldcgrp, newcgrp);
+		}
+	}
+}
+#endif /* CONFIG_MM_OWNER */
+
 /**
  * cgroup_post_fork - called on a new task after adding it to the task list
  * @child: the task in question
diff -puN kernel/exit.c~memory-controller-add-mm-owner kernel/exit.c
--- linux-2.6.25-rc8/kernel/exit.c~memory-controller-add-mm-owner	2008-04-08
17:23:20.000000000 +0530
+++ linux-2.6.25-rc8-balbir/kernel/exit.c	2008-04-10 14:42:11.000000000 +0530
@@ -577,6 +577,88 @@ void exit_fs(struct task_struct *tsk)

 EXPORT_SYMBOL_GPL(exit_fs);

+#ifdef CONFIG_MM_OWNER
+/*
+ * Task p is exiting and it owned mm, lets find a new owner for it
+ */
+static inline int
+mm_need_new_owner(struct mm_struct *mm, struct task_struct *p)
+{
+	/*
+	 * If there are other users of the mm and the owner (us) is exiting
+	 * we need to find a new owner to take on the responsibility.
+	 */
+	if (!mm)
+		return 0;
+	if (atomic_read(&mm->mm_users) <= 1)
+		return 0;
+	if (mm->owner != p)
+		return 0;
+	return 1;
+}
+
+void mm_update_next_owner(struct mm_struct *mm)
+{
+	struct task_struct *c, *g, *p = current;
+
+retry:
+	if (!mm_need_new_owner(mm, p))
+		return;
+
+	read_lock(&tasklist_lock);
+	/*
+	 * Search in the children
+	 */
+	list_for_each_entry(c, &p->children, sibling) {
+		if (c->mm == mm)
+			goto assign_new_owner;
+	}
+
+	/*
+	 * Search in the siblings
+	 */
+	list_for_each_entry(c, &p->parent->children, sibling) {
+		if (c->mm == mm)
+			goto assign_new_owner;
+	}
+
+	/*
+	 * Search through everything else. We should not get
+	 * here often
+	 */
+	do_each_thread(g, c) {
+		if (c->mm == mm)
+			goto assign_new_owner;
+	} while_each_thread(g, c);
+
+	read_unlock(&tasklist_lock);
+	return;
+
+assign_new_owner:
+	BUG_ON(c == p);
+	get_task_struct(c);
+	/*
+	 * The task_lock protects c->mm from changing.
+	 * We always want mm->owner->mm == mm
+	 */
+	task_lock(c);
+	/*
+	 * Delay read_unlock() till we have the task_lock()
+	 * to ensure that c does not slip away underneath us
+	 */
+	read_unlock(&tasklist_lock);
+	if (c->mm != mm) {
+		task_unlock(c);
+		put_task_struct(c);
+		goto retry;
+	}
+	cgroup_mm_owner_callbacks(mm->owner, c);
+	mm->owner = c;
+	task_unlock(c);
+	put_task_struct(c);
+}
+#endif /* CONFIG_MM_OWNER */
+
 /*
  * Turn us into a lazy TLB process if we
  * aren't already..
@@ -616,6 +698,7 @@ static void exit_mm(struct task_struct *
 	/* We don't want this task to be frozen prematurely */
 	clear_freeze_flag(tsk);
 	task_unlock(tsk);
+	mm_update_next_owner(mm);
 	mmput(mm);
 }

diff -puN kernel/fork.c~memory-controller-add-mm-owner kernel/fork.c
--- linux-2.6.25-rc8/kernel/fork.c~memory-controller-add-mm-owner	2008-04-08
17:23:20.000000000 +0530
+++ linux-2.6.25-rc8-balbir/kernel/fork.c	2008-04-08 17:23:20.000000000 +0530
@@ -358,14 +358,13 @@ static struct mm_struct * mm_init(struct
 	mm->ioctx_list = NULL;
 	mm->free_area_cache = TASK_UNMAPPED_BASE;
 	mm->cached_hole_size = ~0UL;
-	mm_init_cgroup(mm, p);
+	mm_init_owner(mm, p);

 	if (likely(!mm_alloc_pgd(mm))) {
 		mm->def_flags = 0;
 		return mm;
 	}

-	mm_free_cgroup(mm);
 	free_mm(mm);
 	return NULL;
 }
@@ -416,7 +415,6 @@ void mmput(struct mm_struct *mm)
 			spin_unlock(&mmlist_lock);
 		}
 		put_swap_token(mm);
-		mm_free_cgroup(mm);
 		mmdrop(mm);
 	}
 }
@@ -996,6 +994,13 @@ static void rt_mutex_init_task(struct ta
 #endif
 }

+#ifdef CONFIG_MM_OWNER
+void mm_init_owner(struct mm_struct *mm, struct task_struct *p)
+{
+	mm->owner = p;
+}
+#endif /* CONFIG_MM_OWNER */
+
 /*
  * This creates a new process as a copy of the old one,
  * but does not actually start it yet.
diff -puN mm/memcontrol.c~memory-controller-add-mm-owner mm/memcontrol.c
--- linux-2.6.25-rc8/mm/memcontrol.c~memory-controller-add-mm-owner	2008-04-08
17:23:20.000000000 +0530
+++ linux-2.6.25-rc8-balbir/mm/memcontrol.c	2008-04-08 17:23:20.000000000 +0530
@@ -238,26 +238,12 @@ static struct mem_cgroup *mem_cgroup_fro
 				css);
 }

-static struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
+struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
 {
 	return container_of(task_subsys_state(p, mem_cgroup_subsys_id),
 				struct mem_cgroup, css);
 }

-void mm_init_cgroup(struct mm_struct *mm, struct task_struct *p)
-{
-	struct mem_cgroup *mem;
-
-	mem = mem_cgroup_from_task(p);
-	css_get(&mem->css);
-	mm->mem_cgroup = mem;
-}
-
-void mm_free_cgroup(struct mm_struct *mm)
-{
-	css_put(&mm->mem_cgroup->css);
-}
-
 static inline int page_cgroup_locked(struct page *page)
 {
 	return bit_spin_is_locked(PAGE_CGROUP_LOCK_BIT, &page->page_cgroup);
@@ -478,6 +464,7 @@ unsigned long mem_cgroup_isolate_pages(u
 	int zid = zone_idx(z);
 	struct mem_cgroup_per_zone *mz;

+	BUG_ON(!mem_cont);
 	mz = mem_cgroup_zoneinfo(mem_cont, nid, zid);
 	if (active)
 		src = &mz->active_list;
@@ -576,7 +563,7 @@ retry:
 		mm = &init_mm;

 	rcu_read_lock();
-	mem = rcu_dereference(mm->mem_cgroup);
+	mem = mem_cgroup_from_task(rcu_dereference(mm->owner));
 	/*
 	 * For every charge from the cgroup, increment reference count
 	 */
@@ -1006,7 +993,6 @@ mem_cgroup_create(struct cgroup_subsys *

 	if (unlikely((cont->parent) == NULL)) {
 		mem = &init_mem_cgroup;
-		init_mm.mem_cgroup = mem;
 		page_cgroup_cache = KMEM_CACHE(page_cgroup, SLAB_PANIC);
 	} else
 		mem = kzalloc(sizeof(struct mem_cgroup), GFP_KERNEL);
@@ -1087,10 +1073,6 @@ static void mem_cgroup_move_task(struct
 	if (!thread_group_leader(p))
 		goto out;

-	css_get(&mem->css);
-	rcu_assign_pointer(mm->mem_cgroup, mem);
-	css_put(&old_mem->css);
-
 out:
 	mmput(mm);
 }
diff -puN init/main.c~memory-controller-add-mm-owner init/main.c
--- linux-2.6.25-rc8/init/main.c~memory-controller-add-mm-owner	2008-04-08
17:23:20.000000000 +0530
+++ linux-2.6.25-rc8-balbir/init/main.c	2008-04-08 17:23:20.000000000 +0530
@@ -537,6 +537,7 @@ asmlinkage void __init start_kernel(void
 	printk(KERN_NOTICE);
 	printk(linux_banner);
 	setup_arch(&command_line);
+	mm_init_owner(&init_mm, &init_task);
 	setup_command_line(command_line);
 	unwind_setup();
 	setup_per_cpu_areas();
_

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL

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-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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