From c4b73aabd0989d93b82894417ae501690bd1db5e Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Thu, 5 Jan 2017 15:17:03 -0500 Subject: [PATCH 1/4] debugobjects: Track number of kmem_cache_alloc/kmem_cache_free done New debugfs stat counters are added to track the numbers of kmem_cache_alloc() and kmem_cache_free() function calls to get a sense of how the internal debug objects cache management is performing. Signed-off-by: Waiman Long Cc: Christian Borntraeger Cc: "Du Changbin" Cc: Andrew Morton Cc: Jan Stancek Link: http://lkml.kernel.org/r/1483647425-4135-2-git-send-email-longman@redhat.com Signed-off-by: Thomas Gleixner --- lib/debugobjects.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/lib/debugobjects.c b/lib/debugobjects.c index 04c1ef717fe0..d78673e7dc56 100644 --- a/lib/debugobjects.c +++ b/lib/debugobjects.c @@ -55,6 +55,12 @@ static int debug_objects_enabled __read_mostly static struct debug_obj_descr *descr_test __read_mostly; +/* + * Track numbers of kmem_cache_alloc and kmem_cache_free done. + */ +static int debug_objects_alloc; +static int debug_objects_freed; + static void free_obj_work(struct work_struct *work); static DECLARE_WORK(debug_obj_work, free_obj_work); @@ -102,6 +108,7 @@ static void fill_pool(void) raw_spin_lock_irqsave(&pool_lock, flags); hlist_add_head(&new->node, &obj_pool); + debug_objects_alloc++; obj_pool_free++; raw_spin_unlock_irqrestore(&pool_lock, flags); } @@ -173,6 +180,7 @@ static void free_obj_work(struct work_struct *work) obj = hlist_entry(obj_pool.first, typeof(*obj), node); hlist_del(&obj->node); obj_pool_free--; + debug_objects_freed++; /* * We release pool_lock across kmem_cache_free() to * avoid contention on pool_lock. @@ -758,6 +766,8 @@ static int debug_stats_show(struct seq_file *m, void *v) seq_printf(m, "pool_min_free :%d\n", obj_pool_min_free); seq_printf(m, "pool_used :%d\n", obj_pool_used); seq_printf(m, "pool_max_used :%d\n", obj_pool_max_used); + seq_printf(m, "objects_alloc :%d\n", debug_objects_alloc); + seq_printf(m, "objects_freed :%d\n", debug_objects_freed); return 0; } From 97dd552eb23c83dbf626a6e84666c7e281375d47 Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Thu, 5 Jan 2017 15:17:04 -0500 Subject: [PATCH 2/4] debugobjects: Scale thresholds with # of CPUs On a large SMP systems with hundreds of CPUs, the current thresholds for allocating and freeing debug objects (256 and 1024 respectively) may not work well. This can cause a lot of needless calls to kmem_aloc() and kmem_free() on those systems. To alleviate this thrashing problem, the object freeing threshold is now increased to "1024 + # of CPUs * 32". Whereas the object allocation threshold is increased to "256 + # of CPUs * 4". That should make the debug objects subsystem scale better with the number of CPUs available in the system. Signed-off-by: Waiman Long Cc: Christian Borntraeger Cc: "Du Changbin" Cc: Andrew Morton Cc: Jan Stancek Link: http://lkml.kernel.org/r/1483647425-4135-3-git-send-email-longman@redhat.com Signed-off-by: Thomas Gleixner --- lib/debugobjects.c | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-) diff --git a/lib/debugobjects.c b/lib/debugobjects.c index d78673e7dc56..dc78217b2199 100644 --- a/lib/debugobjects.c +++ b/lib/debugobjects.c @@ -52,7 +52,10 @@ static int debug_objects_fixups __read_mostly; static int debug_objects_warnings __read_mostly; static int debug_objects_enabled __read_mostly = CONFIG_DEBUG_OBJECTS_ENABLE_DEFAULT; - +static int debug_objects_pool_size __read_mostly + = ODEBUG_POOL_SIZE; +static int debug_objects_pool_min_level __read_mostly + = ODEBUG_POOL_MIN_LEVEL; static struct debug_obj_descr *descr_test __read_mostly; /* @@ -94,13 +97,13 @@ static void fill_pool(void) struct debug_obj *new; unsigned long flags; - if (likely(obj_pool_free >= ODEBUG_POOL_MIN_LEVEL)) + if (likely(obj_pool_free >= debug_objects_pool_min_level)) return; if (unlikely(!obj_cache)) return; - while (obj_pool_free < ODEBUG_POOL_MIN_LEVEL) { + while (obj_pool_free < debug_objects_pool_min_level) { new = kmem_cache_zalloc(obj_cache, gfp); if (!new) @@ -176,7 +179,7 @@ static void free_obj_work(struct work_struct *work) unsigned long flags; raw_spin_lock_irqsave(&pool_lock, flags); - while (obj_pool_free > ODEBUG_POOL_SIZE) { + while (obj_pool_free > debug_objects_pool_size) { obj = hlist_entry(obj_pool.first, typeof(*obj), node); hlist_del(&obj->node); obj_pool_free--; @@ -206,7 +209,7 @@ static void free_object(struct debug_obj *obj) * schedule work when the pool is filled and the cache is * initialized: */ - if (obj_pool_free > ODEBUG_POOL_SIZE && obj_cache) + if (obj_pool_free > debug_objects_pool_size && obj_cache) sched = 1; hlist_add_head(&obj->node, &obj_pool); obj_pool_free++; @@ -1126,4 +1129,11 @@ void __init debug_objects_mem_init(void) pr_warn("out of memory.\n"); } else debug_objects_selftest(); + + /* + * Increase the thresholds for allocating and freeing objects + * according to the number of possible CPUs available in the system. + */ + debug_objects_pool_size += num_possible_cpus() * 32; + debug_objects_pool_min_level += num_possible_cpus() * 4; } From 858274b6a13b4db0e6fb451eea7f8817c42426a7 Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Thu, 5 Jan 2017 15:17:05 -0500 Subject: [PATCH 3/4] debugobjects: Reduce contention on the global pool_lock On a large SMP system with many CPUs, the global pool_lock may become a performance bottleneck as all the CPUs that need to allocate or free debug objects have to take the lock. That can sometimes cause soft lockups like: NMI watchdog: BUG: soft lockup - CPU#35 stuck for 22s! [rcuos/1:21] ... RIP: 0010:[] [] _raw_spin_unlock_irqrestore+0x3b/0x60 ... Call Trace: [] free_object+0x81/0xb0 [] debug_check_no_obj_freed+0x193/0x220 [] ? trace_hardirqs_on_caller+0xf9/0x1c0 [] ? file_free_rcu+0x36/0x60 [] kmem_cache_free+0xd2/0x380 [] ? fput+0x90/0x90 [] file_free_rcu+0x36/0x60 [] rcu_nocb_kthread+0x1b3/0x550 [] ? rcu_nocb_kthread+0x101/0x550 [] ? sync_exp_work_done.constprop.63+0x50/0x50 [] kthread+0x101/0x120 [] ? trace_hardirqs_on_caller+0xf9/0x1c0 [] ret_from_fork+0x22/0x50 To reduce the amount of contention on the pool_lock, the actual kmem_cache_free() of the debug objects will be delayed if the pool_lock is busy. This will temporarily increase the amount of free objects available at the free pool when the system is busy. As a result, the number of kmem_cache allocation and freeing is reduced. To further reduce the lock operations free debug objects in batches of four. Signed-off-by: Waiman Long Cc: Christian Borntraeger Cc: "Du Changbin" Cc: Andrew Morton Cc: Jan Stancek Link: http://lkml.kernel.org/r/1483647425-4135-4-git-send-email-longman@redhat.com Signed-off-by: Thomas Gleixner --- lib/debugobjects.c | 32 +++++++++++++++++++++++--------- 1 file changed, 23 insertions(+), 9 deletions(-) diff --git a/lib/debugobjects.c b/lib/debugobjects.c index dc78217b2199..5e1bf2f4a5ec 100644 --- a/lib/debugobjects.c +++ b/lib/debugobjects.c @@ -172,25 +172,39 @@ alloc_object(void *addr, struct debug_bucket *b, struct debug_obj_descr *descr) /* * workqueue function to free objects. + * + * To reduce contention on the global pool_lock, the actual freeing of + * debug objects will be delayed if the pool_lock is busy. We also free + * the objects in a batch of 4 for each lock/unlock cycle. */ +#define ODEBUG_FREE_BATCH 4 + static void free_obj_work(struct work_struct *work) { - struct debug_obj *obj; + struct debug_obj *objs[ODEBUG_FREE_BATCH]; unsigned long flags; + int i; - raw_spin_lock_irqsave(&pool_lock, flags); - while (obj_pool_free > debug_objects_pool_size) { - obj = hlist_entry(obj_pool.first, typeof(*obj), node); - hlist_del(&obj->node); - obj_pool_free--; - debug_objects_freed++; + if (!raw_spin_trylock_irqsave(&pool_lock, flags)) + return; + while (obj_pool_free >= debug_objects_pool_size + ODEBUG_FREE_BATCH) { + for (i = 0; i < ODEBUG_FREE_BATCH; i++) { + objs[i] = hlist_entry(obj_pool.first, + typeof(*objs[0]), node); + hlist_del(&objs[i]->node); + } + + obj_pool_free -= ODEBUG_FREE_BATCH; + debug_objects_freed += ODEBUG_FREE_BATCH; /* * We release pool_lock across kmem_cache_free() to * avoid contention on pool_lock. */ raw_spin_unlock_irqrestore(&pool_lock, flags); - kmem_cache_free(obj_cache, obj); - raw_spin_lock_irqsave(&pool_lock, flags); + for (i = 0; i < ODEBUG_FREE_BATCH; i++) + kmem_cache_free(obj_cache, objs[i]); + if (!raw_spin_trylock_irqsave(&pool_lock, flags)) + return; } raw_spin_unlock_irqrestore(&pool_lock, flags); } From 0cad93c3453fc9d11692d3924ac3a520821bbf64 Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Tue, 7 Feb 2017 16:40:30 -0500 Subject: [PATCH 4/4] debugobjects: Improve variable naming As suggested by Ingo, the debug_objects_alloc counter is now renamed to debug_objects_allocated with minor twist in comment and debug output. Signed-off-by: Waiman Long Cc: Andrew Morton Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1486503630-1501-1-git-send-email-longman@redhat.com Signed-off-by: Ingo Molnar --- lib/debugobjects.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/lib/debugobjects.c b/lib/debugobjects.c index 5e1bf2f4a5ec..8c28cbd7e104 100644 --- a/lib/debugobjects.c +++ b/lib/debugobjects.c @@ -59,9 +59,9 @@ static int debug_objects_pool_min_level __read_mostly static struct debug_obj_descr *descr_test __read_mostly; /* - * Track numbers of kmem_cache_alloc and kmem_cache_free done. + * Track numbers of kmem_cache_alloc()/free() calls done. */ -static int debug_objects_alloc; +static int debug_objects_allocated; static int debug_objects_freed; static void free_obj_work(struct work_struct *work); @@ -111,7 +111,7 @@ static void fill_pool(void) raw_spin_lock_irqsave(&pool_lock, flags); hlist_add_head(&new->node, &obj_pool); - debug_objects_alloc++; + debug_objects_allocated++; obj_pool_free++; raw_spin_unlock_irqrestore(&pool_lock, flags); } @@ -783,8 +783,8 @@ static int debug_stats_show(struct seq_file *m, void *v) seq_printf(m, "pool_min_free :%d\n", obj_pool_min_free); seq_printf(m, "pool_used :%d\n", obj_pool_used); seq_printf(m, "pool_max_used :%d\n", obj_pool_max_used); - seq_printf(m, "objects_alloc :%d\n", debug_objects_alloc); - seq_printf(m, "objects_freed :%d\n", debug_objects_freed); + seq_printf(m, "objs_allocated:%d\n", debug_objects_allocated); + seq_printf(m, "objs_freed :%d\n", debug_objects_freed); return 0; }