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Subject[PATCH] kfree_rcu() should use the new kfree_bulk() interface for freeing rcu structures
Date
From: Rao Shoaib <rao.shoaib@oracle.com>

This patch updates kfree_rcu to use new bulk memory free functions as they
are more efficient. It also moves kfree_call_rcu() out of rcu related code to
mm/slab_common.c

Signed-off-by: Rao Shoaib <rao.shoaib@oracle.com>
---
include/linux/mm.h | 5 ++
kernel/rcu/tree.c | 14 ----
kernel/sysctl.c | 40 +++++++++++
mm/slab.h | 23 +++++++
mm/slab_common.c | 198 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
5 files changed, 264 insertions(+), 16 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ea818ff..8ae4f25 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2669,5 +2669,10 @@ void __init setup_nr_node_ids(void);
static inline void setup_nr_node_ids(void) {}
#endif

+extern int sysctl_kfree_rcu_drain_limit;
+extern int sysctl_kfree_rcu_poll_limit;
+extern int sysctl_kfree_rcu_empty_limit;
+extern int sysctl_kfree_rcu_caching_allowed;
+
#endif /* __KERNEL__ */
#endif /* _LINUX_MM_H */
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index f9c0ca2..69951ef 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3209,20 +3209,6 @@ void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
EXPORT_SYMBOL_GPL(call_rcu_bh);

/*
- * Queue an RCU callback for lazy invocation after a grace period.
- * This will likely be later named something like "call_rcu_lazy()",
- * but this change will require some way of tagging the lazy RCU
- * callbacks in the list of pending callbacks. Until then, this
- * function may only be called from __kfree_rcu().
- */
-void kfree_call_rcu(struct rcu_head *head,
- rcu_callback_t func)
-{
- __call_rcu(head, func, rcu_state_p, -1, 1);
-}
-EXPORT_SYMBOL_GPL(kfree_call_rcu);
-
-/*
* Because a context switch is a grace period for RCU-sched and RCU-bh,
* any blocking grace-period wait automatically implies a grace period
* if there is only one CPU online at any point time during execution
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 557d467..47b48f7 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1655,6 +1655,46 @@ static struct ctl_table vm_table[] = {
.extra2 = (void *)&mmap_rnd_compat_bits_max,
},
#endif
+ {
+ .procname = "kfree_rcu_drain_limit",
+ .data = &sysctl_kfree_rcu_drain_limit,
+ .maxlen = sizeof(sysctl_kfree_rcu_drain_limit),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &one,
+ .extra2 = &one_hundred,
+ },
+
+ {
+ .procname = "kfree_rcu_poll_limit",
+ .data = &sysctl_kfree_rcu_poll_limit,
+ .maxlen = sizeof(sysctl_kfree_rcu_poll_limit),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &one,
+ .extra2 = &one_hundred,
+ },
+
+ {
+ .procname = "kfree_rcu_empty_limit",
+ .data = &sysctl_kfree_rcu_empty_limit,
+ .maxlen = sizeof(sysctl_kfree_rcu_empty_limit),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &zero,
+ .extra2 = &four,
+ },
+
+ {
+ .procname = "kfree_rcu_caching_allowed",
+ .data = &sysctl_kfree_rcu_caching_allowed,
+ .maxlen = sizeof(sysctl_kfree_rcu_caching_allowed),
+ .mode = 0644,
+ .proc_handler = proc_dointvec_minmax,
+ .extra1 = &zero,
+ .extra2 = &one,
+ },
+
{ }
};

diff --git a/mm/slab.h b/mm/slab.h
index ad657ff..2541f70 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -78,6 +78,29 @@ extern const struct kmalloc_info_struct {
unsigned long size;
} kmalloc_info[];

+#define RCU_MAX_ACCUMULATE_SIZE 25
+
+struct rcu_bulk_free_container {
+ struct rcu_head rbfc_rcu;
+ int rbfc_entries;
+ void *rbfc_data[RCU_MAX_ACCUMULATE_SIZE];
+ struct rcu_bulk_free *rbfc_rbf;
+};
+
+struct rcu_bulk_free {
+ struct rcu_head rbf_rcu; /* used to schedule monitor process */
+ spinlock_t rbf_lock;
+ struct rcu_bulk_free_container *rbf_container;
+ struct rcu_bulk_free_container *rbf_cached_container;
+ struct rcu_head *rbf_list_head;
+ int rbf_list_size;
+ int rbf_cpu;
+ int rbf_empty;
+ int rbf_polled;
+ bool rbf_init;
+ bool rbf_monitor;
+};
+
unsigned long calculate_alignment(slab_flags_t flags,
unsigned long align, unsigned long size);

diff --git a/mm/slab_common.c b/mm/slab_common.c
index c8cb367..06fd12c 100644
--- a/mm/slab_common.c
+++ b/mm/slab_common.c
@@ -20,6 +20,7 @@
#include <asm/tlbflush.h>
#include <asm/page.h>
#include <linux/memcontrol.h>
+#include <linux/types.h>

#define CREATE_TRACE_POINTS
#include <trace/events/kmem.h>
@@ -129,6 +130,7 @@ int __kmem_cache_alloc_bulk(struct kmem_cache *s, gfp_t flags, size_t nr,

for (i = 0; i < nr; i++) {
void *x = p[i] = kmem_cache_alloc(s, flags);
+
if (!x) {
__kmem_cache_free_bulk(s, i, p);
return 0;
@@ -353,6 +355,7 @@ unsigned long calculate_alignment(slab_flags_t flags,
*/
if (flags & SLAB_HWCACHE_ALIGN) {
unsigned long ralign = cache_line_size();
+
while (size <= ralign / 2)
ralign /= 2;
align = max(align, ralign);
@@ -444,9 +447,8 @@ kmem_cache_create(const char *name, size_t size, size_t align,
mutex_lock(&slab_mutex);

err = kmem_cache_sanity_check(name, size);
- if (err) {
+ if (err)
goto out_unlock;
- }

/* Refuse requests with allocator specific flags */
if (flags & ~SLAB_FLAGS_PERMITTED) {
@@ -1131,6 +1133,7 @@ EXPORT_SYMBOL(kmalloc_order);
void *kmalloc_order_trace(size_t size, gfp_t flags, unsigned int order)
{
void *ret = kmalloc_order(size, flags, order);
+
trace_kmalloc(_RET_IP_, ret, size, PAGE_SIZE << order, flags);
return ret;
}
@@ -1483,6 +1486,197 @@ void kzfree(const void *p)
}
EXPORT_SYMBOL(kzfree);

+static DEFINE_PER_CPU(struct rcu_bulk_free, cpu_rbf);
+
+/* drain if atleast these many objects */
+int sysctl_kfree_rcu_drain_limit __read_mostly = 10;
+
+/* time to poll if fewer than drain_limit */
+int sysctl_kfree_rcu_poll_limit __read_mostly = 5;
+
+/* num of times to check bfr exit */
+int sysctl_kfree_rcu_empty_limit __read_mostly = 2;
+
+int sysctl_kfree_rcu_caching_allowed __read_mostly = 1;
+
+/* RCU call back function. Frees the memory */
+static void
+__rcu_bulk_free_impl(struct rcu_head *rbfc_rcu)
+{
+ struct rcu_bulk_free *rbf = NULL;
+ struct rcu_bulk_free_container *rbfc = container_of(rbfc_rcu,
+ struct rcu_bulk_free_container, rbfc_rcu);
+
+ WARN_ON(rbfc->rbfc_entries <= 0);
+ kfree_bulk(rbfc->rbfc_entries, rbfc->rbfc_data);
+
+ rbf = rbfc->rbfc_rbf;
+ if (!sysctl_kfree_rcu_caching_allowed ||
+ cmpxchg(&rbf->rbf_cached_container, NULL, rbfc) != NULL) {
+ kfree(rbfc);
+ }
+}
+
+/* processes list of rcu structures
+ * used when conatiner can not be allocated
+ */
+
+static void
+__rcu_bulk_schedule_list(struct rcu_bulk_free *rbf)
+{
+ int i = 0;
+
+ for (i = 0; i < rbf->rbf_list_size; i++) {
+ struct rcu_head *free_head;
+
+ free_head = rbf->rbf_list_head;
+ rbf->rbf_list_head = free_head->next;
+ free_head->next = NULL;
+ call_rcu(free_head, free_head->func);
+ }
+ WARN_ON(rbf->rbf_list_head != NULL);
+ rbf->rbf_list_size = 0;
+}
+
+
+/* RCU monitoring function -- submits elements for RCU reclaim */
+static void
+__rcu_bulk_free_monitor(struct rcu_head *rbf_rcu)
+{
+ struct rcu_bulk_free *rbf = NULL;
+ struct rcu_bulk_free_container *rbfc = NULL;
+
+ rbf = container_of(rbf_rcu, struct rcu_bulk_free, rbf_rcu);
+
+ spin_lock(&rbf->rbf_lock);
+
+ rbfc = rbf->rbf_container;
+
+ if (rbf->rbf_list_size > 0) {
+ WARN_ON(rbfc != NULL);
+ if ((rbf->rbf_list_size >= sysctl_kfree_rcu_drain_limit) ||
+ rbf->rbf_polled >= sysctl_kfree_rcu_poll_limit) {
+ rbf->rbf_polled = 0;
+ __rcu_bulk_schedule_list(rbf);
+ } else {
+ rbf->rbf_polled++;
+ }
+ } else if (rbfc != NULL) {
+ WARN_ON(rbfc->rbfc_entries <= 0);
+ if ((rbfc->rbfc_entries > sysctl_kfree_rcu_drain_limit) ||
+ rbf->rbf_polled++ >= sysctl_kfree_rcu_poll_limit) {
+ rbf->rbf_polled = 0;
+ call_rcu(&rbfc->rbfc_rcu, __rcu_bulk_free_impl);
+ rbf->rbf_container = NULL;
+ }
+ } else {
+ /* Nothing to do, keep track */
+ rbf->rbf_empty++;
+ }
+
+ if (rbf->rbf_empty >= sysctl_kfree_rcu_empty_limit) {
+ rbf->rbf_monitor = false;
+ rbf->rbf_empty = 0;
+ }
+
+ spin_unlock(&rbf->rbf_lock);
+
+ if (rbf->rbf_monitor)
+ call_rcu(&rbf->rbf_rcu, __rcu_bulk_free_monitor);
+}
+
+/* Main RCU function that is called to free RCU structures */
+static void
+__rcu_bulk_free(struct rcu_head *head, rcu_callback_t func, int cpu, bool lazy)
+{
+ unsigned long offset;
+ void *ptr;
+ struct rcu_bulk_free *rbf;
+ struct rcu_bulk_free_container *rbfc = NULL;
+
+ rbf = this_cpu_ptr(&cpu_rbf);
+
+ if (unlikely(!rbf->rbf_init)) {
+ spin_lock_init(&rbf->rbf_lock);
+ rbf->rbf_cpu = smp_processor_id();
+ rbf->rbf_init = true;
+ }
+
+ /* hold lock to protect against other cpu's */
+ spin_lock_bh(&rbf->rbf_lock);
+
+ rbfc = rbf->rbf_container;
+
+ if (rbfc == NULL) {
+ if (rbf->rbf_cached_container == NULL) {
+ rbf->rbf_container =
+ kmalloc(sizeof(struct rcu_bulk_free_container),
+ GFP_ATOMIC);
+ rbf->rbf_container->rbfc_rbf = rbf;
+ } else {
+ rbf->rbf_container = rbf->rbf_cached_container;
+ rbf->rbf_container->rbfc_rbf = rbf;
+ cmpxchg(&rbf->rbf_cached_container,
+ rbf->rbf_cached_container, NULL);
+ }
+
+ if (unlikely(rbf->rbf_container == NULL)) {
+
+ /* Memory allocation failed maintain a list */
+
+ head->func = (void *)func;
+ head->next = rbf->rbf_list_head;
+ rbf->rbf_list_head = head;
+ rbf->rbf_list_size++;
+ if (rbf->rbf_list_size == RCU_MAX_ACCUMULATE_SIZE)
+ __rcu_bulk_schedule_list(rbf);
+
+ goto done;
+ }
+
+ rbfc = rbf->rbf_container;
+ rbfc->rbfc_entries = 0;
+
+ if (rbf->rbf_list_head != NULL)
+ __rcu_bulk_schedule_list(rbf);
+ }
+
+ offset = (unsigned long)func;
+ ptr = (void *)head - offset;
+
+ rbfc->rbfc_data[rbfc->rbfc_entries++] = ptr;
+ if (rbfc->rbfc_entries == RCU_MAX_ACCUMULATE_SIZE) {
+
+ WRITE_ONCE(rbf->rbf_container, NULL);
+ spin_unlock_bh(&rbf->rbf_lock);
+ call_rcu(&rbfc->rbfc_rcu, __rcu_bulk_free_impl);
+ return;
+ }
+
+done:
+ if (!rbf->rbf_monitor) {
+
+ call_rcu(&rbf->rbf_rcu, __rcu_bulk_free_monitor);
+ rbf->rbf_monitor = true;
+ }
+
+ spin_unlock_bh(&rbf->rbf_lock);
+}
+
+/*
+ * Queue an RCU callback for lazy invocation after a grace period.
+ * This will likely be later named something like "call_rcu_lazy()",
+ * but this change will require some way of tagging the lazy RCU
+ * callbacks in the list of pending callbacks. Until then, this
+ * function may only be called from __kfree_rcu().
+ */
+void kfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
+{
+ __rcu_bulk_free(head, func, -1, 1);
+}
+EXPORT_SYMBOL_GPL(kfree_call_rcu);
+
+
/* Tracepoints definitions. */
EXPORT_TRACEPOINT_SYMBOL(kmalloc);
EXPORT_TRACEPOINT_SYMBOL(kmem_cache_alloc);
--
2.7.4
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