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SubjectRe: [PATCH] lockdep: reduce stack_trace usage
On Fri, Apr 23, 2010 at 09:40:44PM +0800, Yong Zhang wrote:
> Hi John,
>
> (checking mail at home).
> I find some place which can be hacked. Below is the patch.
> But I don't even compile it. Can you test it to see if it can smooth
> your problem.
>
> ---cut here ---
> >From 6b9d513b7c417c0805ef0acc1cb3227bddba0889 Mon Sep 17 00:00:00 2001
> From: Yong Zhang <yong.zhang0@gmail.com>
> Date: Fri, 23 Apr 2010 21:13:54 +0800
> Subject: [PATCH] lockdep: reduce stack_trace usage
>
> When calling check_prevs_add(), if all validations passed
> add_lock_to_list() will add new lock to dependency tree and
> alloc stack_trace for each list_entry. But at this time,
> we are always on the same stack, so stack_trace for each
> list_entry has the same value. This is redundant and eats up
> lots of memory which could lead to warning on low
> MAX_STACK_TRACE_ENTRIES.
> Using one copy of stack_trace instead.

With the following test patch running on my machine:
> cat /proc/lockdep_stats
lock-classes: 564 [max: 8191]
direct dependencies: 2626 [max: 16384]
indirect dependencies: 5951
all direct dependencies: 48226
dependency chains: 2576 [max: 32768]
dependency chain hlocks: 6740 [max: 163840]
in-hardirq chains: 18
in-softirq chains: 163
in-process chains: 2395
stack-trace entries: 63076 [max: 262144]
duplicated stack-trace entries: 7592 <=========
combined max dependencies: 7465936
hardirq-safe locks: 30
hardirq-unsafe locks: 380
softirq-safe locks: 82
softirq-unsafe locks: 305
irq-safe locks: 90
irq-unsafe locks: 380
hardirq-read-safe locks: 0
hardirq-read-unsafe locks: 51
softirq-read-safe locks: 11
softirq-read-unsafe locks: 40
irq-read-safe locks: 11
irq-read-unsafe locks: 51
uncategorized locks: 112
unused locks: 1
max locking depth: 15
max bfs queue depth: 83
debug_locks: 1

We can see that about 12% stack_trace usage can be reduced.

Thanks,
Yong

------lockdep-duplicated-stack_trace-detect.patch------
diff --git a/kernel/lockdep.c b/kernel/lockdep.c
index 2594e1c..dfd37ea 100644
--- a/kernel/lockdep.c
+++ b/kernel/lockdep.c
@@ -369,6 +369,7 @@ static int verbose(struct lock_class *class)
* addresses. Protected by the graph_lock.
*/
unsigned long nr_stack_trace_entries;
+unsigned long nr_duplicated_stack_trace_entries;
static unsigned long stack_trace[MAX_STACK_TRACE_ENTRIES];

static int save_trace(struct stack_trace *trace)
@@ -818,9 +819,14 @@ static struct lock_list *alloc_list_entry(void)
* Add a new dependency to the head of the list:
*/
static int add_lock_to_list(struct lock_class *class, struct lock_class *this,
- struct list_head *head, unsigned long ip, int distance)
+ struct list_head *head, unsigned long ip,
+ int distance, struct held_lock *next)
{
struct lock_list *entry;
+ static struct held_lock *hlock;
+ static struct stack_trace trace;
+ int i;
+
/*
* Lock not present yet - get a new dependency struct and
* add it to the list:
@@ -834,6 +840,20 @@ static int add_lock_to_list(struct lock_class *class, struct lock_class *this,

entry->class = this;
entry->distance = distance;
+
+ if (hlock != next) {
+ hlock = next;
+ trace = entry->trace;
+ } else if (trace.nr_entries == entry->trace.nr_entries &&
+ trace.max_entries == entry->trace.max_entries) {
+ /* start from 2 to skip the stack introduced by lockdep */
+ for (i=2; i<trace.nr_entries; i++) {
+ if (trace.entries[i] != entry->trace.entries[i])
+ goto no_duplicated;
+ }
+ nr_duplicated_stack_trace_entries += trace.nr_entries;
+ }
+no_duplicated:
/*
* Since we never remove from the dependency list, the list can
* be walked lockless by other CPUs, it's only allocation
@@ -1694,14 +1714,14 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
*/
ret = add_lock_to_list(hlock_class(prev), hlock_class(next),
&hlock_class(prev)->locks_after,
- next->acquire_ip, distance);
+ next->acquire_ip, distance, next);

if (!ret)
return 0;

ret = add_lock_to_list(hlock_class(next), hlock_class(prev),
&hlock_class(next)->locks_before,
- next->acquire_ip, distance);
+ next->acquire_ip, distance, next);
if (!ret)
return 0;

diff --git a/kernel/lockdep_internals.h b/kernel/lockdep_internals.h
index a2ee95a..d00fe7b 100644
--- a/kernel/lockdep_internals.h
+++ b/kernel/lockdep_internals.h
@@ -84,6 +84,7 @@ extern unsigned long nr_list_entries;
extern unsigned long nr_lock_chains;
extern int nr_chain_hlocks;
extern unsigned long nr_stack_trace_entries;
+extern unsigned long nr_duplicated_stack_trace_entries;

extern unsigned int nr_hardirq_chains;
extern unsigned int nr_softirq_chains;
diff --git a/kernel/lockdep_proc.c b/kernel/lockdep_proc.c
index d4aba4f..32cb9a3 100644
--- a/kernel/lockdep_proc.c
+++ b/kernel/lockdep_proc.c
@@ -307,6 +307,8 @@ static int lockdep_stats_show(struct seq_file *m, void *v)
nr_process_chains);
seq_printf(m, " stack-trace entries: %11lu [max: %lu]\n",
nr_stack_trace_entries, MAX_STACK_TRACE_ENTRIES);
+ seq_printf(m, " duplicated stack-trace entries:%11lu\n",
+ nr_duplicated_stack_trace_entries);
seq_printf(m, " combined max dependencies: %11u\n",
(nr_hardirq_chains + 1) *
(nr_softirq_chains + 1) *
> Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: David S. Miller <davem@davemloft.net>
> ---
> kernel/lockdep.c | 20 ++++++++++++--------
> 1 files changed, 12 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/lockdep.c b/kernel/lockdep.c
> index 2594e1c..097d5fb 100644
> --- a/kernel/lockdep.c
> +++ b/kernel/lockdep.c
> @@ -818,7 +818,8 @@ static struct lock_list *alloc_list_entry(void)
> * Add a new dependency to the head of the list:
> */
> static int add_lock_to_list(struct lock_class *class, struct lock_class *this,
> - struct list_head *head, unsigned long ip, int distance)
> + struct list_head *head, unsigned long ip,
> + int distance, struct stack_trace *trace)
> {
> struct lock_list *entry;
> /*
> @@ -829,11 +830,9 @@ static int add_lock_to_list(struct lock_class *class, struct lock_class *this,
> if (!entry)
> return 0;
>
> - if (!save_trace(&entry->trace))
> - return 0;
> -
> entry->class = this;
> entry->distance = distance;
> + entry->trace = *trace;
> /*
> * Since we never remove from the dependency list, the list can
> * be walked lockless by other CPUs, it's only allocation
> @@ -1635,7 +1634,7 @@ check_deadlock(struct task_struct *curr, struct held_lock *next,
> */
> static int
> check_prev_add(struct task_struct *curr, struct held_lock *prev,
> - struct held_lock *next, int distance)
> + struct held_lock *next, int distance, struct stack_trace *trace)
> {
> struct lock_list *entry;
> int ret;
> @@ -1694,14 +1693,14 @@ check_prev_add(struct task_struct *curr, struct held_lock *prev,
> */
> ret = add_lock_to_list(hlock_class(prev), hlock_class(next),
> &hlock_class(prev)->locks_after,
> - next->acquire_ip, distance);
> + next->acquire_ip, distance, trace);
>
> if (!ret)
> return 0;
>
> ret = add_lock_to_list(hlock_class(next), hlock_class(prev),
> &hlock_class(next)->locks_before,
> - next->acquire_ip, distance);
> + next->acquire_ip, distance, trace);
> if (!ret)
> return 0;
>
> @@ -1732,6 +1731,7 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)
> {
> int depth = curr->lockdep_depth;
> struct held_lock *hlock;
> + struct stack_trace trace;
>
> /*
> * Debugging checks.
> @@ -1748,6 +1748,9 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)
> curr->held_locks[depth-1].irq_context)
> goto out_bug;
>
> + if (!save_trace(&trace))
> + return 0;
> +
> for (;;) {
> int distance = curr->lockdep_depth - depth + 1;
> hlock = curr->held_locks + depth-1;
> @@ -1756,7 +1759,8 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next)
> * added:
> */
> if (hlock->read != 2) {
> - if (!check_prev_add(curr, hlock, next, distance))
> + if (!check_prev_add(curr, hlock, next,
> + distance, &trace))
> return 0;
> /*
> * Stop after the first non-trylock entry,
> --
> 1.6.3.3


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