Kernel memory accounting container (v3)

Long time ago we decided to start memory control with the user memory container. Now this container in -mm tree and I think we can start with (at least discussion of) the kmem one.

Changes from v.2:
* introduced generic notifiers for slub. right now there are only events, needed by accounting, but this set can be extended in the future;
* moved the controller core into separate file, so that its extension and/or porting on slAb will look more logical;
* fixed this message :).

Changes from v.1:
* fixed Paul's comment about subsystem registration;
* return ERR_PTR from ->create callback, not NULL;
* make container-to-object assignment in rcu-safe section;
* make turning accounting on and off with "1" and "0".

============================================================

First of all - why do we need this kind of control. The major "pros" is that kernel memory control protects the system from DoS attacks by processes that live in container. As our experience shows many exploits simply do not work in the container with limited kernel memory.

I can split the kernel memory container into 4 parts:

1. kmalloc-ed objects control
2. vmalloc-ed objects control
3. buddy allocated pages control
4. kmem_cache_alloc-ed objects control

the control of first tree types of objects has one peculiarity:
one need to explicitly point out which allocations he wants to account and this becomes not-configurable and is to be discussed.

On the other hands such objects as anon_vma-s, file-s, sighangds, vfsmounts, etc are created by user request always and should always be accounted. Fortunately they are allocated from their own caches and thus the whole kmem cache can be accountable.

This is exactly what this patchset does - it adds the ability to account for the total size of kmem-cache-allocated objects from specified kmem caches.

This is based on the SLUB allocator, Paul's containers and the resource counters I made for RSS controller and which are in -mm tree already.

To play with it, one need to mount the container file system with -o kmem and then mark some caches as accountable via /sys/slab/<cache_name>/cache_account.

As I have already told kmalloc caches cannot be accounted easily so turning the accounting on for them will fail with -EINVAL. Turning the accounting off is possible only if the cache has no objects. This is done so because turning accounting off implies unaccounting of all the objects in the cache, but due to full-pages in slub are not stored in any lists (usually) this is impossible to do so, however I'm open for discussion of how to make this work.

The patches are applicable to the latest Morton's tree.

Thanks,
Pavel

According to Christoph, there are already multiple people who want to control slab allocations and track memory for various reasons. So this is an introduction of such a hooks.

The selected method of notification is srcu notifier blocks. This is selected because the "call" path, i.e. when the notification is done, is lockless and at the same time notification handlers can sleep. Neither regular nor atomic notifiers provide such facilities.

The events tracked are:
1. allocation of an object
2. freeing of an onbject
3. allocation of a new page for objects
4. freeing this page

More events can be added on demand.

The kmem cache marked with SLAB_NOTIFY flag will cause all the events above to generate notifications. By default no caches come with this flag.

To preserve the fast-paths and keep the stack from growing the checks for the flag are made in a separate inline functions and the actual notification is done in noinline ones.

Hopefully, this looks close to how Christoph sees it :)

---

 include/linux/slab.h     |    1 
 include/linux/slub_def.h |   16 +++++++
 mm/slub.c                |  105 ++++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 121 insertions(+), 1 deletion(-)

index 3a5bad3..a3bd620 100644
@@ -28,6 +28,7 @@
 #define SLAB_DESTROY_BY_RCU	0x00080000UL	/* Defer freeing slabs to RCU */
 #define SLAB_MEM_SPREAD		0x00100000UL	/* Spread some memory over cpuset */
 #define SLAB_TRACE		0x00200000UL	/* Trace allocations and frees */
+#define SLAB_NOTIFY		0x00400000UL	/* Notify major events */
 
 /* The following flags affect the page allocator grouping pages by mobility */
 #define SLAB_RECLAIM_ACCOUNT	0x00020000UL		/* Objects are reclaimable */

index d65159d..547777e 100644
@@ -200,4 +202,20 @@ static __always_inline void *kmalloc_nod
 }
 #endif
 
+struct slub_notify_struct {
+	struct kmem_cache *cachep;
+	void *objp;
+	gfp_t gfp;
+};
+
+enum {
+	SLUB_ALLOC,
+	SLUB_FREE,
+	SLUB_NEWPAGE,
+	SLUB_FREEPAGE,
+};
+
+int slub_register_notifier(struct notifier_block *nb);
+void slub_unregister_notifier(struct notifier_block *nb);
+
 #endif /* _LINUX_SLUB_DEF_H */

That's true, but:
1. we perform only a flag check on a fast path
2. currently we cannot force the freeing of an object to go _always_ through the slow __slab_free(), and thus the following situation is possible:
a. container A allocates an object and this object is
accounted to it
b. the object is freed and gets into lockless freelist (but
stays accounted to A)
c. container C allocates this object from the freelist
and thus get unaccounted amount of memory
this discrepancy can grow up infinitely. Sure, we can mark some caches to go through the slow path even on freeing the objects, but isn't it the same as checking for SLAB_NOTIFY on fast paths?

Maybe it's worth having the notifiers under config option, so that those who don't need this won't suffer at all?

Thanks,
Pavel

This is still going to slow down everyone else and I still think there is no need to do that.

At that point you could mark the slab as a slow slab by setting SLAB_DEBUG() so we always take the slow path for this slab.

B wont work if SLAB_DEBUG() is set. The fastpath is then disabled.

The other caches will then still perform up to speed.

I think you would want the container functionality to be available in distros. They may make the choice whether to enable the container functionality based on its impact. It is good if we can stash it away so that there is a negligible performance impact if its compiled in but off.

[snip]

I have run the kernbench test on the kernels with a) containers support and b) containers and kmem accounting support but (!) turned off. The results are:

                 a)             b)
Elapsed Time     768.500000     767.050000
User Time        679.360000     679.240000
System Time      87.020000      86.950000
Percent CPU      99.000000      99.000000
Context Switches 376891.000000  375407.000000
Sleeps           385377.000000  385426.000000

The test run was kernbench -n 1 -o 4 -M, the node is i386 DualCore Xeon 3.2GHz with 2Gb of RAM.

so the fast path is still fast, and we have two ways:
1. we keep the checks on the fastpath and have 0 overhead for unaccounted caches and some overhead for accounted;
2. we move the checks into the slow one and have 0 overhead for unaccounted caches and huge overhead for accounted.

I admit that I messed something, so shall I measure some other activity or use another HW?

Thanks,
Pavel

This stuff accumulates. I have a bad experience from SLAB. We are counting cycle counts and cachelines touched in the fastpath and this is going to add to them.

Huge? Its not that huge.

You could use this module to test the cycles in the fastpath:

/* test-slub.c
*/

#include <linux/jiffies.h>
#include <linux/compiler.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/calc64.h>
#include <asm/timex.h>
#include <asm/system.h>

#define TEST_COUNT 10000

#define PARALLEL

#ifdef PARALLEL
#include <linux/completion.h>
#include <linux/sched.h>
#include <linux/workqueue.h>
#include <linux/kthread.h>

struct test_struct {
	struct task_struct *task;
	int cpu;
	int size;
	int count;
	void **v;
	void (*test_p1)(struct test_struct *);
	void (*test_p2)(struct test_struct *);
	unsigned long start;
	unsigned long stop1;
	unsigned long stop2;
} test[NR_CPUS];

/*
* Allocate TEST_COUNT objects and later free them all again */
static void kmalloc_alloc_then_free_test_p1(struct test_struct *t)

{
	int i;

	for (i = 0; i < t->count; i++)
		t->v[i] = kmalloc(t->size, GFP_KERNEL);
}

static void kmalloc_alloc_then_free_test_p2(struct test_struct *t)

{
	int i;

	for (i = 0; i < t->count; i++)
		kfree(t->v[i]);
}

/*
* Allocate TEST_COUNT objects. Free them immediately. */
static void kmalloc_alloc_free_test_p1(struct test_struct *t)

{
	int i;

	for (i = 0; i < TEST_COUNT; i++)
		kfree(kmalloc(t->size, GFP_KERNEL));
}

static atomic_t tests_running;
static DECLARE_COMPLETION(completion);
static int started;

static int test_func(void *private)

{
	struct test_struct *t = private;
	cpumask_t newmask = CPU_MASK_NONE;

        cpu_set(t->cpu, newmask);
        set_cpus_allowed(current, newmask);
	t->v = kmalloc(t->count * sizeof(void *), GFP_KERNEL);

	atomic_inc(&tests_running);
	wait_for_completion(&completion);
	t->start = get_cycles();
	t->test_p1(t);
	t->stop1 = get_cycles();
	if (t->test_p2)
		t->test_p2(t);
	t->stop2 = get_cycles();
	kfree(t->v);
	atomic_dec(&tests_running);
	set_current_state(TASK_UNINTERRUPTIBLE);
	schedule();
	return 0;
}

static void do_concurrent_test(void (*p1)(struct test_struct *),

		void (*p2)(struct test_struct *),
		int size, const char *name)
{
	int cpu;
	unsigned long time1 = 0;
	unsigned long time2 = 0;
	unsigned long sum1 = 0;
	unsigned long sum2 = 0;

	atomic_set(&tests_running, 0);
	started = 0;
	init_completion(&completion);

	for_each_online_cpu(cpu) {
		struct test_struct *t = &test[cpu];

		t->cpu = cpu;
		t->count = TEST_COUNT;
		t->test_p1 = p1;
		t->test_p2 = p2;
		t->size = size;
		t->task = kthread_run(test_func, t, "test%d", cpu);
		if (IS_ERR(t->task)) {
			printk("Failed to start test func\n");
			return;
		}
	}

	/* Wait till all processes are running */
	while (atomic_read(&tests_running) < num_online_cpus()) {
		set_current_state(TASK_UNINTERRUPTIBLE);
		schedule_timeout(10);
	}
	complete_all(&completion);
	while (atomic_read(&tests_running)) {
		set_current_state(TASK_UNINTERRUPTIBLE);
		schedule_timeout(10);
	}

	for_each_online_cpu(cpu)
		kthread_stop(test[cpu].task);

	printk(KERN_ALERT "%s(%d):", name, size);
	for_each_online_cpu(cpu) {
		struct test_struct *t = &test[cpu];

		time1 = t->stop1 - t->start;
		time2 = t->stop2 - t->stop1;
		sum1 += time1;
		sum2 += time2;
		printk(" %d=%lu", cpu, time1 / TEST_COUNT);
		if (p2)
			printk("/%lu", time2 / TEST_COUNT);
	}
	printk(" Average=%lu", sum1 / num_online_cpus() / TEST_COUNT);
	if (p2)
		printk("/%lu", sum2 / num_online_cpus() / TEST_COUNT);
	printk("\n");
	schedule_timeout(200);
}

#endif

static int slub_test_init(void)

{
	void **v = kmalloc(TEST_COUNT * sizeof(void *), GFP_KERNEL);
	unsigned int i;
	cycles_t time1, time2, time;
	long rem;
	int size;

	printk(KERN_ALERT "test init\n");

	printk(KERN_ALERT "Single thread testing\n");
	printk(KERN_ALERT "=====================\n");
	printk(KERN_ALERT "1. Kmalloc: Repeatedly allocate then free test\n");
	for (size = 8; size <= PAGE_SIZE << 2; size <<= 1) {
		time1 = get_cycles();
		for (i = 0; i < TEST_COUNT; i++) {
			v[i] = kmalloc(size, GFP_KERNEL);
		}
		time2 = get_cycles();
		time = time2 - time1;

		printk(KERN_ALERT "%i times kmalloc(%d) ", i, size);
		time = div_long_long_rem(time, TEST_COUNT, &rem);
		printk("-> %llu cycles ", time);

		time1 = get_cycles();
		for (i = 0; i < TEST_COUNT; i++) {
			kfree(v[i]);
		}
		time2 = get_cycles();
		time = time2 - time1;

		printk("kfree ");
		time = div_long_long_rem(time, TEST_COUNT, &rem);
		printk("-> %llu cycles\n", time);
	}

	printk(KERN_ALERT "2. Kmalloc: alloc/free test\n");
	for (size = 8; size <= PAGE_SIZE << 2; size <<= 1) {
		time1 = get_cycles();
		for (i = 0; i < TEST_COUNT; i++) {
			kfree(kmalloc(size, GFP_KERNEL));
		}
		time2 = get_cycles();
		time = time2 - time1;

		printk(KERN_ALERT "%i times kmalloc(%d)/kfree ", i, size);
		time = div_long_long_rem(time, TEST_COUNT, &rem);
		printk("-> %llu cycles\n", time);
	}
	kfree(v);
#ifdef PARALLEL
	printk(KERN_INFO "Concurrent allocs\n");
	printk(KERN_INFO "=================\n");
	for (i = 3; i <= PAGE_SHIFT; i++) {
		do_concurrent_test(kmalloc_alloc_then_free_test_p1,
			kmalloc_alloc_then_free_test_p2,
			1 << i, "Kmalloc N*alloc N*free");
	}
	for (i = 3; i <= PAGE_SHIFT; i++) {
		do_concurrent_test(kmalloc_alloc_free_test_p1, NULL,
			1 << i, "Kmalloc N*(alloc free)");
	}

#endif

return -EAGAIN; /* Fail will directly unload the module */
}

static void slub_test_exit(void)

{
	printk(KERN_ALERT "test exit\n");
}

module_init(slub_test_init)
module_exit(slub_test_exit)

MODULE_LICENSE("GPL");
MODULE_AUTHOR("Mathieu Desnoyers");
MODULE_DESCRIPTION("SLUB test");

The /sys/slab/<name>/cache_notify attribute controls whether the cache <name> is to be accounted or not.

For the reasons described before kmalloc caches cannot be turned on.

By default no caches are accountable. Simply make

  # echo -n 1 >  /sys/slab/<name>cache_notify
to turn notification of this cache on.

If we turn accounting on on some cache and this cache is merged with some other, this "other" will be notified as well. We can solve this by disabling of cache merging, but maybe we can do it some other way.

Turning the notification off is possible only when this cache is empty. The reason for this is that the pages, that are full of objects are not linked in any list, so we wouldn't be able to walk these pages and notify others that these objects are no longer tracked.

---

 mm/slub.c |   45 +++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 45 insertions(+)

index 1802645..bfb7c21 100644
@@ -2338,6 +2440,14 @@ EXPORT_SYMBOL(kmem_cache_destroy);
 struct kmem_cache kmalloc_caches[PAGE_SHIFT] __cacheline_aligned;
 EXPORT_SYMBOL(kmalloc_caches);
 
+static inline int is_kmalloc_cache(struct kmem_cache *s)
+{
+	int km_idx;
+
+	km_idx = s - kmalloc_caches;
+	return km_idx >= 0 && km_idx < ARRAY_SIZE(kmalloc_caches);
+}
+
 #ifdef CONFIG_ZONE_DMA
 static struct kmem_cache *kmalloc_caches_dma[PAGE_SHIFT];
 #endif

@@ -3753,6 +3874,42 @@ static ssize_t defrag_ratio_store(struct
 SLAB_ATTR(defrag_ratio);
 #endif
 
+static ssize_t cache_notify_show(struct kmem_cache *s, char *buf)
+{
+	return sprintf(buf, "%d\n", !!(s->flags & SLAB_NOTIFY));
+}
+
+static ssize_t cache_notify_store(struct kmem_cache *s,
+		const char *buf, size_t length)
+{
+	if (buf[0] == '1') {
+		if (is_kmalloc_cache(s))
+			/*
+			 * cannot just make these caches accountable
+			 */
+			return -EINVAL;
+
+		s->flags |= SLAB_NOTIFY;
+		return length;
+	}
+
+	if (buf[0] == '0') {
+		if (any_slab_objects(s))
+			/*
+			 * we cannot turn this off because of the
+			 * full slabs cannot be found in this case
+			 */
+			return -EBUSY;
+
+		s->flags &= ~SLAB_NOTIFY;
+		return length;
+	}
+
+	return -EINVAL;
+}
+
+SLAB_ATTR(cache_notify);
+
 static struct attribute * slab_attrs[] = {
 	&slab_size_attr.attr,
 	&object_size_attr.attr,

@@ -3783,6 +3940,7 @@ static struct attribute * slab_attrs[] =
 #ifdef CONFIG_NUMA
 	&defrag_ratio_attr.attr,
 #endif
+	&cache_notify_attr.attr,
 	NULL
 };

You could write a 1 to slub_nomerge during bootup if containers are to be supported? Once they are merged it is going to be difficult to separate them again.

Yes. I also thought that disabling the merge is the only way to handle this case. Thanks.

No no! This is not that I meant here. This is just like the redzoning turning on/off dynamically.

I meant that we cannot find the pages that are full of objects to notify others that these ones are no longer tracked. I know that we can do it by tracking these pages with some performance penalty, but does it worth having the ability to turn notifications off by the cost of the performance degradation?

Thanks,
Pavel

Not sure. That may be your call.

Attach the controller to the containers. This will work with the SLUB allocator only. However, if we need I can port this on SLAB (and maybe SLOB ;) ).

This setup is simple and stupid.

---

 include/linux/container_subsys.h |    6 +
 init/Kconfig                     |    6 +
 mm/Makefile                      |    1 
 mm/kmemcontrol.c                 |  123 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 136 insertions(+)

index 81d11c2..9dd90d9 100644
@@ -36,3 +36,9 @@ SUBSYS(mem_container)
 #endif
 
 /* */
+
+#ifdef CONFIG_CONTAINER_KMEM
+SUBSYS(kmem)
+#endif
+
+/* */

index 58559ea..d499f15 100644
@@ -353,6 +353,12 @@ config CONTAINER_MEM_CONT
 	  Provides a memory controller that manages both page cache and
 	  RSS memory.
 
+config CONTAINER_KMEM
+	bool "Kernel memory controller for containers"
+	depends on CONTAINERS && RESOURCE_COUNTERS && SLUB
+	help
+	  Provides a kernel memory usage control for containers
+
 config PROC_PID_CPUSET
 	bool "Include legacy /proc/<pid>/cpuset file"
 	depends on CPUSETS

index 6237dd6..1cb7e6d 100644
@@ -31,4 +31,5 @@ obj-$(CONFIG_MIGRATION) += migrate.o
 obj-$(CONFIG_SMP) += allocpercpu.o
 obj-$(CONFIG_QUICKLIST) += quicklist.o
 obj-$(CONFIG_CONTAINER_MEM_CONT) += memcontrol.o
+obj-$(CONFIG_CONTAINER_KMEM) += kmemcontrol.o
 

The struct page gets an extra pointer (just like it has with the RSS controller) and this pointer points to the array of the kmem_container pointers - one for each object stored on that page itself.

Thus the i'th object on the page is accounted to the container pointed by the i'th pointer on that array and when the object is freed we unaccount its size to this particular container, not the container current task belongs to.

This is done so, because the context objects are freed is most often not the same as the one this objects was allocated in (due to RCU and reference counters).

---

 include/linux/mm_types.h |    7 ++
 include/linux/slub_def.h |    2 
 mm/kmemcontrol.c         |  126 +++++++++++++++++++++++++++++++++++++++++++++++
 mm/slub.c                |   12 ++++
 4 files changed, 145 insertions(+), 2 deletions(-)

index 48df4b4..1a41901 100644
@@ -83,9 +83,14 @@ struct page {
 	void *virtual;			/* Kernel virtual address (NULL if
 					   not kmapped, ie. highmem) */
 #endif /* WANT_PAGE_VIRTUAL */
+	union {
 #ifdef CONFIG_CONTAINER_MEM_CONT
-	unsigned long page_container;
+		unsigned long page_container;
+#endif
+#ifdef CONFIG_CONTAINER_KMEM
+		struct kmem_container **containers;
 #endif
+	};
 #ifdef CONFIG_PAGE_OWNER
 	int order;
 	unsigned int gfp_mask;

index d65159d..547777e 100644
@@ -69,6 +69,8 @@ struct kmem_cache {
 #endif
 };
 
+int slab_index(void *p, struct kmem_cache *s, void *addr);
+
 /*
  * Kmalloc subsystem.
  */

new file mode 100644
index 0000000..637554b
@@ -0,6 +1,9 @@
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
+ *
+ * Changelog:
+ *   2007 Pavel Emelyanov : Add slub accounting
  */
 
 #include <linux/mm.h>

@@ -0,2 +123,126 @@
 	.subsys_id = kmem_subsys_id,
 	.early_init = 1,

};
+
+/*
+ * slub accounting
+ */
+
+static int kmem_prepare(struct kmem_cache *s, struct page *pg, gfp_t flags) +{
+ struct kmem_container **ptr;
+
+ ptr = kzalloc(s->objects * sizeof(struct kmem_container *), flags);
+ if (ptr == NULL)
+ return -ENOMEM;
+
+ pg->containers = ptr;
+ return 0;
+}
+
+static void kmem_release(struct kmem_cache *s, struct page *pg)
+{
+ struct kmem_container **ptr;
+
+ ptr = pg->containers;
+ if (ptr == NULL)
+ return;
+
+ kfree(ptr);
+ pg->containers = NULL;
+}
+
+static int kmem_charge(struct kmem_cache *s, void *obj, gfp_t gfp) +{
+ struct page *pg;
+ struct kmem_container *cnt;
+ struct kmem_container **obj_container;
+
+ pg = virt_to_head_page(obj);
+ obj_container = pg->containers;
+ if (unlikely(obj_container == NULL)) {
+ /*
+ * turned on after some objects were allocated
+ */
+ if (kmem_prepare(s, pg, gfp) < 0)
+ goto err;
+
+ obj_container = pg->containers;
+ }
+
+ rcu_read_lock();
+ cnt = task_kmem_container(current);
+ if (res_counter_charge(&cnt->res, s->size))
+ goto err_locked;
+
+ css_get(&cnt->css);
+ rcu_read_unlock();
+ obj_container[slab_index(obj, s, page_address(pg))] = cnt;
+ return 0;
+
+err_locked:
+ rcu_read_unlock();
+err:
+ return -ENOMEM;
+}
+
+static void kmem_uncharge(struct kmem_cache *s, void *obj)
+{
+ struct page *pg;
+ struct kmem_container *cnt;
+ struct kmem_container **obj_container;
+
+ pg = virt_to_head_page(obj);
+ obj_container = pg->containers;
+ if (obj_container == NULL)
+ return;
+
+ obj_container += slab_index(obj, s, page_address(pg));
+ cnt = *obj_container;
+ if (cnt == NULL)
+ return;
+
+ res_counter_uncharge(&cnt->res, s->size);
+ *obj_container = NULL;
+ css_put(&cnt->css);
+}
+
+static int kmem_notify(struct notifier_block *nb, unsigned long cmd, void *arg) +{
+ int ret;
+ struct slub_notify_struct *ns;
+
+ ns = (struct slub_notify_struct *)arg;
+
+ switch (cmd) {
+ case SLUB_ALLOC:
+ ret = kmem_charge(ns->cachep, ns->objp, ns->gfp);
+ break;
+ case SLUB_FREE:
+ ret = 0;
+ kmem_uncharge(ns->cachep, ns->objp);
+ break;
+ case SLUB_NEWPAGE:
+ ret = kmem_prepare(ns->cachep, ns->objp, ns->gfp);
+ break;
+ case SLUB_FREEPAGE:
+ ret = 0;
+ kmem_release(ns->cachep, ns->objp);
+ break;
+ default:
+ return NOTIFY_DONE;
+ }
+
+ return (ret < 0) ? notifier_from_errno(ret) : NOTIFY_OK;
+}
+
+static struct notifier_block kmem_block = {
+ .notifier_call = kmem_notify,
+};
+
+static int kmem_subsys_register(void)
+{
+ return slub_register_notifier(&kmem_block);
+}
+
+__initcall(kmem_subsys_register);

index 1802645..bfb7c21 100644
@@ -327,7 +327,7 @@ static inline void set_freepointer(struc
 	for (__p = (__free); __p; __p = get_freepointer((__s), __p))
 
 /* Determine object index from a given position */
-static inline int slab_index(void *p, struct kmem_cache *s, void *addr)
+inline int slab_index(void *p, struct kmem_cache *s, void *addr)
 {
 	return (p - addr) / s->size;
 }

@@ -2789,6 +2900,16 @@ static int slab_unmergeable(struct kmem_
 	if (s->refcount < 0)
 		return 1;
 
+#ifdef CONFIG_CONTAINER_KMEM
+	/*
+	 * many caches that can be accountable are usually merged with
+	 * kmalloc caches, which are disabled for accounting for a while
+	 */
+
+	if (is_kmalloc_cache(s))
+		return 1;
+#endif
+
 	return 0;
 }

Can't these at least be unioned so we don't make it any _worse_ when both are turned on?

-- Dave

Your comment makes me suspect, that you don't look at the patches at all :(

They ARE unioned.

No big fat comment here - this all is containers API.

Where can I find more information why is would not be possible to account kmalloc caches?

Hi, Christoph,

I've wondered the same thing and asked the question. Pavel wrote back to me saying

"The pages that are full of objects are not linked in any list in kmem_cache so we just cannot find them."

I suspect that SLUB changes this, but I need to look at the allocator more carefully.

	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL

That is true for any types of slab cache and not restricted to kmalloc slabs. SLUB can be switched into a mode where it provides these lists (again at a performance penalty).

But I thought we generate the counters at alloc and free time? So why do we need to traverse the object lists?

When we make echo 0 > /sys/slab/xxx/cache_notify we want all the objects to be unaccounted back immediately. Even __free_slab() won't catch this because the SLAB_NOTIFY flag will be turned off for this cache. So we have to walk all the objects and unaccount them.

It is possible, but the problem is that we want to account only allocations explicitly caused by the user request. E.g. the vfsmount name is kmalloc-ed by explicit user request, but such things as buffer heads are not.

So we have to explicitly specify which calls to kmalloc() do we wand to be accounted and which we do not by passing additional flag (GFP_ACCT?) to kmalloc, but this is another patch.

Yet again - as soon as we agree on the implementation of kmem caches accounting, I will proceed with working on kmalloc, vmalloc and buddy allocator.

Thanks,
Pavel

Oh gosh..... Lots of complications in the allocator paths.