Create a memory pool for temporary tracepoint probes storage

[deliverable/lttng-modules.git] / lttng-tp-mempool.c

diff --git a/lttng-tp-mempool.c b/lttng-tp-mempool.c
new file mode 100644 (file)
index 0000000..d984bd4
--- /dev/null
+++ b/lttng-tp-mempool.c
@@ -0,0 +1,172 @@
+/*
+ * lttng-tp-mempool.c
+ *
+ * Copyright (C) 2018 Julien Desfossez <jdesfossez@efficios.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; only
+ * version 2.1 of the License.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <linux/slab.h>
+#include <linux/percpu.h>
+
+#include <lttng-tp-mempool.h>
+
+struct lttng_tp_buf_entry {
+       int cpu; /* To make sure we return the entry to the right pool. */
+       char buf[LTTNG_TP_MEMPOOL_BUF_SIZE];
+       struct list_head list;
+};
+
+/*
+ * No exclusive access strategy for now, this memory pool is currently only
+ * used from a non-preemptible context, and the interrupt tracepoint probes do
+ * not use this facility.
+ */
+struct per_cpu_buf {
+       struct list_head free_list; /* Free struct lttng_tp_buf_entry. */
+};
+
+static struct per_cpu_buf __percpu *pool; /* Per-cpu buffer. */
+
+int lttng_tp_mempool_init(void)
+{
+       int ret, cpu;
+
+       /* The pool is only supposed to be allocated once. */
+       if (pool) {
+               WARN_ON_ONCE(1);
+               ret = -1;
+               goto end;
+       }
+
+       pool = alloc_percpu(struct per_cpu_buf);
+       if (!pool) {
+               ret = -ENOMEM;
+               goto end;
+       }
+
+       for_each_possible_cpu(cpu) {
+               struct per_cpu_buf *cpu_buf = per_cpu_ptr(pool, cpu);
+
+               INIT_LIST_HEAD(&cpu_buf->free_list);
+       }
+
+       for_each_possible_cpu(cpu) {
+               int i;
+               struct per_cpu_buf *cpu_buf = per_cpu_ptr(pool, cpu);
+
+               for (i = 0; i < LTTNG_TP_MEMPOOL_NR_BUF_PER_CPU; i++) {
+                       struct lttng_tp_buf_entry *entry;
+
+                       entry = kzalloc(sizeof(struct lttng_tp_buf_entry),
+                                       GFP_KERNEL);
+                       if (!entry) {
+                               ret = -ENOMEM;
+                               goto error_free_pool;
+                       }
+                       entry->cpu = cpu;
+                       list_add_tail(&entry->list, &cpu_buf->free_list);
+               }
+       }
+
+       ret = 0;
+       goto end;
+
+error_free_pool:
+       lttng_tp_mempool_destroy();
+end:
+       return ret;
+}
+
+void lttng_tp_mempool_destroy(void)
+{
+       int cpu;
+
+       if (!pool) {
+               return;
+       }
+
+       for_each_possible_cpu(cpu) {
+               struct per_cpu_buf *cpu_buf = per_cpu_ptr(pool, cpu);
+               struct lttng_tp_buf_entry *entry, *tmp;
+               int i = 0;
+
+               list_for_each_entry_safe(entry, tmp, &cpu_buf->free_list, list) {
+                       list_del(&entry->list);
+                       kfree(entry);
+                       i++;
+               }
+               if (i < LTTNG_TP_MEMPOOL_NR_BUF_PER_CPU) {
+                       printk(KERN_WARNING "Leak detected in tp-mempool\n");
+               }
+       }
+       free_percpu(pool);
+       pool = NULL;
+}
+
+void *lttng_tp_mempool_alloc(size_t size)
+{
+       void *ret;
+       struct lttng_tp_buf_entry *entry;
+       struct per_cpu_buf *cpu_buf;
+       int cpu = smp_processor_id();
+
+       if (size > LTTNG_TP_MEMPOOL_BUF_SIZE) {
+               ret = NULL;
+               goto end;
+       }
+
+       cpu_buf = per_cpu_ptr(pool, cpu);
+       if (list_empty(&cpu_buf->free_list)) {
+               ret = NULL;
+               goto end;
+       }
+
+       entry = list_first_entry(&cpu_buf->free_list, struct lttng_tp_buf_entry, list);
+       /* Remove the entry from the free list. */
+       list_del(&entry->list);
+
+       memset(entry->buf, 0, LTTNG_TP_MEMPOOL_BUF_SIZE);
+
+       ret = (void *) entry->buf;
+
+end:
+       return ret;
+}
+
+void lttng_tp_mempool_free(void *ptr)
+{
+       struct lttng_tp_buf_entry *entry;
+       struct per_cpu_buf *cpu_buf;
+
+       if (!ptr) {
+               goto end;
+       }
+
+       entry = container_of(ptr, struct lttng_tp_buf_entry, buf);
+       if (!entry) {
+               goto end;
+       }
+
+       cpu_buf = per_cpu_ptr(pool, entry->cpu);
+       if (!cpu_buf) {
+               goto end;
+       }
+       /* Add it to the free list. */
+       list_add_tail(&entry->list, &cpu_buf->free_list);
+
+end:
+       return;
+}