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mm: kmemleak: optimise kmemleak_lock acquiring during kmemleak_scan

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The kmemleak memory scanning uses finer grained object->lock spinlocks
primarily to avoid races with the memory block freeing.  However, the
pointer lookup in the rb tree requires the kmemleak_lock to be held.
This is currently done in the find_and_get_object() function for each
pointer-like location read during scanning.  While this allows a low
latency on kmemleak_*() callbacks on other CPUs, the memory scanning is
slower.

This patch moves the kmemleak_lock outside the scan_block() loop,
acquiring/releasing it only once per scanned memory block.  The
allow_resched logic is moved outside scan_block() and a new
scan_large_block() function is implemented which splits large blocks in
MAX_SCAN_SIZE chunks with cond_resched() calls in-between.  A redundant
(object->flags & OBJECT_NO_SCAN) check is also removed from
scan_object().

With this patch, the kmemleak scanning performance is significantly
improved: at least 50% with lock debugging disabled and over an order of
magnitude with lock proving enabled (on an arm64 system).

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Catalin Marinas 2015-06-24 16:58:37 -07:00 committed by Linus Torvalds
parent 9d5a4c730d
commit 93ada579b0
1 changed files with 56 additions and 34 deletions
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90
mm/kmemleak.c
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@ -53,10 +53,12 @@
* modifications to the memory scanning parameters including the scan_thread
* pointer
*
* Locks and mutexes should only be acquired/nested in the following order:
* Locks and mutexes are acquired/nested in the following order:
*
* scan_mutex -> object->lock -> other_object->lock (SINGLE_DEPTH_NESTING)
* -> kmemleak_lock
* scan_mutex [-> object->lock] -> kmemleak_lock -> other_object->lock (SINGLE_DEPTH_NESTING)
*
* No kmemleak_lock and object->lock nesting is allowed outside scan_mutex
* regions.
*
* The kmemleak_object structures have a use_count incremented or decremented
* using the get_object()/put_object() functions. When the use_count becomes
@ -490,8 +492,7 @@ static struct kmemleak_object *find_and_get_object(unsigned long ptr, int alias)
rcu_read_lock();
read_lock_irqsave(&kmemleak_lock, flags);
if (ptr >= min_addr && ptr < max_addr)
object = lookup_object(ptr, alias);
object = lookup_object(ptr, alias);
read_unlock_irqrestore(&kmemleak_lock, flags);
/* check whether the object is still available */
@ -1170,19 +1171,18 @@ static int scan_should_stop(void)
* found to the gray list.
*/
static void scan_block(void *_start, void *_end,
struct kmemleak_object *scanned, int allow_resched)
struct kmemleak_object *scanned)
{
unsigned long *ptr;
unsigned long *start = PTR_ALIGN(_start, BYTES_PER_POINTER);
unsigned long *end = _end - (BYTES_PER_POINTER - 1);
unsigned long flags;
read_lock_irqsave(&kmemleak_lock, flags);
for (ptr = start; ptr < end; ptr++) {
struct kmemleak_object *object;
unsigned long flags;
unsigned long pointer;
if (allow_resched)
cond_resched();
if (scan_should_stop())
break;
@ -1195,26 +1195,31 @@ static void scan_block(void *_start, void *_end,
pointer = *ptr;
kasan_enable_current();
object = find_and_get_object(pointer, 1);
if (pointer < min_addr || pointer >= max_addr)
continue;
/*
* No need for get_object() here since we hold kmemleak_lock.
* object->use_count cannot be dropped to 0 while the object
* is still present in object_tree_root and object_list
* (with updates protected by kmemleak_lock).
*/
object = lookup_object(pointer, 1);
if (!object)
continue;
if (object == scanned) {
if (object == scanned)
/* self referenced, ignore */
put_object(object);
continue;
}
/*
* Avoid the lockdep recursive warning on object->lock being
* previously acquired in scan_object(). These locks are
* enclosed by scan_mutex.
*/
spin_lock_irqsave_nested(&object->lock, flags,
SINGLE_DEPTH_NESTING);
spin_lock_nested(&object->lock, SINGLE_DEPTH_NESTING);
if (!color_white(object)) {
/* non-orphan, ignored or new */
spin_unlock_irqrestore(&object->lock, flags);
put_object(object);
spin_unlock(&object->lock);
continue;
}
@ -1226,13 +1231,27 @@ static void scan_block(void *_start, void *_end,
*/
object->count++;
if (color_gray(object)) {
/* put_object() called when removing from gray_list */
WARN_ON(!get_object(object));
list_add_tail(&object->gray_list, &gray_list);
spin_unlock_irqrestore(&object->lock, flags);
continue;
}
spin_unlock(&object->lock);
}
read_unlock_irqrestore(&kmemleak_lock, flags);
}
spin_unlock_irqrestore(&object->lock, flags);
put_object(object);
/*
* Scan a large memory block in MAX_SCAN_SIZE chunks to reduce the latency.
*/
static void scan_large_block(void *start, void *end)
{
void *next;
while (start < end) {
next = min(start + MAX_SCAN_SIZE, end);
scan_block(start, next, NULL);
start = next;
cond_resched();
}
}
@ -1258,22 +1277,25 @@ static void scan_object(struct kmemleak_object *object)
if (hlist_empty(&object->area_list)) {
void *start = (void *)object->pointer;
void *end = (void *)(object->pointer + object->size);
void *next;
while (start < end && (object->flags & OBJECT_ALLOCATED) &&
!(object->flags & OBJECT_NO_SCAN)) {
scan_block(start, min(start + MAX_SCAN_SIZE, end),
object, 0);
start += MAX_SCAN_SIZE;
do {
next = min(start + MAX_SCAN_SIZE, end);
scan_block(start, next, object);
start = next;
if (start >= end)
break;
spin_unlock_irqrestore(&object->lock, flags);
cond_resched();
spin_lock_irqsave(&object->lock, flags);
}
} while (object->flags & OBJECT_ALLOCATED);
} else
hlist_for_each_entry(area, &object->area_list, node)
scan_block((void *)area->start,
(void *)(area->start + area->size),
object, 0);
object);
out:
spin_unlock_irqrestore(&object->lock, flags);
}
@ -1350,14 +1372,14 @@ static void kmemleak_scan(void)
rcu_read_unlock();
/* data/bss scanning */
scan_block(_sdata, _edata, NULL, 1);
scan_block(__bss_start, __bss_stop, NULL, 1);
scan_large_block(_sdata, _edata);
scan_large_block(__bss_start, __bss_stop);
#ifdef CONFIG_SMP
/* per-cpu sections scanning */
for_each_possible_cpu(i)
scan_block(__per_cpu_start + per_cpu_offset(i),
__per_cpu_end + per_cpu_offset(i), NULL, 1);
scan_large_block(__per_cpu_start + per_cpu_offset(i),
__per_cpu_end + per_cpu_offset(i));
#endif
/*
@ -1378,7 +1400,7 @@ static void kmemleak_scan(void)
/* only scan if page is in use */
if (page_count(page) == 0)
continue;
scan_block(page, page + 1, NULL, 1);
scan_block(page, page + 1, NULL);
}
}
put_online_mems();
@ -1392,7 +1414,7 @@ static void kmemleak_scan(void)
read_lock(&tasklist_lock);
do_each_thread(g, p) {
scan_block(task_stack_page(p), task_stack_page(p) +
THREAD_SIZE, NULL, 0);
THREAD_SIZE, NULL);
} while_each_thread(g, p);
read_unlock(&tasklist_lock);
}