Basing on the lib/objpool.c, change it to something like a
ptrpool, so that we can utilize that to test the correctness
and performance of the page_frag.
The testing is done by ensuring that the fragments allocated
from a frag_frag_cache instance is pushed into a ptrpool
instance in a kthread binded to the first cpu, and a kthread
binded to the current node will pop the fragmemt from the
ptrpool and call page_frag_alloc_va() to free the fragmemt.
We may refactor out the common part between objpool and ptrpool
if this ptrpool thing turns out to be helpful for other place.
Signed-off-by: Yunsheng Lin <linyunsheng@xxxxxxxxxx>
---
mm/Kconfig.debug | 8 +
mm/Makefile | 1 +
mm/page_frag_test.c | 364 ++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 373 insertions(+)
create mode 100644 mm/page_frag_test.c
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index afc72fde0f03..1ebcd45f47d4 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -142,6 +142,14 @@ config DEBUG_PAGE_REF
kernel code. However the runtime performance overhead is virtually
nil until the tracepoints are actually enabled.
+config DEBUG_PAGE_FRAG_TEST
+ tristate "Test module for page_frag"
+ default n
+ depends on m && DEBUG_KERNEL
+ help
+ This builds the "page_frag_test" module that is used to test the
+ correctness and performance of page_frag's implementation.
+
config DEBUG_RODATA_TEST
bool "Testcase for the marking rodata read-only"
depends on STRICT_KERNEL_RWX
diff --git a/mm/Makefile b/mm/Makefile
index 4abb40b911ec..5a14e6992f44 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -101,6 +101,7 @@ obj-$(CONFIG_MEMORY_FAILURE) += memory-failure.o
obj-$(CONFIG_HWPOISON_INJECT) += hwpoison-inject.o
obj-$(CONFIG_DEBUG_KMEMLEAK) += kmemleak.o
obj-$(CONFIG_DEBUG_RODATA_TEST) += rodata_test.o
+obj-$(CONFIG_DEBUG_PAGE_FRAG_TEST) += page_frag_test.o
obj-$(CONFIG_DEBUG_VM_PGTABLE) += debug_vm_pgtable.o
obj-$(CONFIG_PAGE_OWNER) += page_owner.o
obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o
diff --git a/mm/page_frag_test.c b/mm/page_frag_test.c
new file mode 100644
index 000000000000..6743db672dad
--- /dev/null
+++ b/mm/page_frag_test.c
@@ -0,0 +1,364 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Test module for page_frag cache
+ *
+ * Copyright: linyunsheng@xxxxxxxxxx
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/atomic.h>
+#include <linux/irqflags.h>
+#include <linux/cpumask.h>
+#include <linux/log2.h>
+#include <linux/completion.h>
+#include <linux/kthread.h>
+
+#define OBJPOOL_NR_OBJECT_MAX BIT(24)
+
+struct objpool_slot {
+ u32 head;
+ u32 tail;
+ u32 last;
+ u32 mask;
+ void *entries[];
+} __packed;
+
+struct objpool_head {
+ int nr_cpus;
+ int capacity;
+ struct objpool_slot **cpu_slots;
+};
+
+/* initialize percpu objpool_slot */
+static void objpool_init_percpu_slot(struct objpool_head *pool,
+ struct objpool_slot *slot)
+{
+ /* initialize elements of percpu objpool_slot */
+ slot->mask = pool->capacity - 1;
+}
+
+/* allocate and initialize percpu slots */
+static int objpool_init_percpu_slots(struct objpool_head *pool,
+ int nr_objs, gfp_t gfp)
+{
+ int i;
+
+ for (i = 0; i < pool->nr_cpus; i++) {
+ struct objpool_slot *slot;
+ int size;
+
+ /* skip the cpu node which could never be present */
+ if (!cpu_possible(i))
+ continue;
+
+ size = struct_size(slot, entries, pool->capacity);
+
+ /*
+ * here we allocate percpu-slot & objs together in a single
+ * allocation to make it more compact, taking advantage of
+ * warm caches and TLB hits. in default vmalloc is used to
+ * reduce the pressure of kernel slab system. as we know,
+ * minimal size of vmalloc is one page since vmalloc would
+ * always align the requested size to page size
+ */
+ if (gfp & GFP_ATOMIC)
+ slot = kmalloc_node(size, gfp, cpu_to_node(i));
+ else
+ slot = __vmalloc_node(size, sizeof(void *), gfp,
+ cpu_to_node(i),
+ __builtin_return_address(0));
+ if (!slot)
+ return -ENOMEM;
+
+ memset(slot, 0, size);
+ pool->cpu_slots[i] = slot;
+
+ objpool_init_percpu_slot(pool, slot);
+ }
+
+ return 0;
+}
+
+/* cleanup all percpu slots of the object pool */
+static void objpool_fini_percpu_slots(struct objpool_head *pool)
+{
+ int i;
+
+ if (!pool->cpu_slots)
+ return;
+
+ for (i = 0; i < pool->nr_cpus; i++)
+ kvfree(pool->cpu_slots[i]);
+ kfree(pool->cpu_slots);
+}
+
+/* initialize object pool and pre-allocate objects */
+static int objpool_init(struct objpool_head *pool, int nr_objs, gfp_t gfp)
+{
+ int rc, capacity, slot_size;
+
+ /* check input parameters */
+ if (nr_objs <= 0 || nr_objs > OBJPOOL_NR_OBJECT_MAX)
+ return -EINVAL;
+
+ /* calculate capacity of percpu objpool_slot */
+ capacity = roundup_pow_of_two(nr_objs);
+ if (!capacity)
+ return -EINVAL;
+
+ gfp = gfp & ~__GFP_ZERO;
+
+ /* initialize objpool pool */
+ memset(pool, 0, sizeof(struct objpool_head));
+ pool->nr_cpus = nr_cpu_ids;
+ pool->capacity = capacity;
+ slot_size = pool->nr_cpus * sizeof(struct objpool_slot *);
+ pool->cpu_slots = kzalloc(slot_size, gfp);
+ if (!pool->cpu_slots)
+ return -ENOMEM;
+
+ /* initialize per-cpu slots */
+ rc = objpool_init_percpu_slots(pool, nr_objs, gfp);
+ if (rc)
+ objpool_fini_percpu_slots(pool);
+
+ return rc;
+}
+
+/* adding object to slot, abort if the slot was already full */
+static int objpool_try_add_slot(void *obj, struct objpool_head *pool, int cpu)
+{
+ struct objpool_slot *slot = pool->cpu_slots[cpu];
+ u32 head, tail;
+
+ /* loading tail and head as a local snapshot, tail first */
+ tail = READ_ONCE(slot->tail);
+
+ do {
+ head = READ_ONCE(slot->head);
+ /* fault caught: something must be wrong */
+ if (unlikely(tail - head >= pool->capacity))
+ return -ENOSPC;
+ } while (!try_cmpxchg_acquire(&slot->tail, &tail, tail + 1));
+
+ /* now the tail position is reserved for the given obj */
+ WRITE_ONCE(slot->entries[tail & slot->mask], obj);
+ /* update sequence to make this obj available for pop() */
+ smp_store_release(&slot->last, tail + 1);
+
+ return 0;
+}
+
+/* reclaim an object to object pool */
+static int objpool_push(void *obj, struct objpool_head *pool)
+{
+ unsigned long flags;
+ int rc;
+
+ /* disable local irq to avoid preemption & interruption */
+ raw_local_irq_save(flags);
+ rc = objpool_try_add_slot(obj, pool, raw_smp_processor_id());
+ raw_local_irq_restore(flags);
+
+ return rc;
+}
+
+/* try to retrieve object from slot */
+static void *objpool_try_get_slot(struct objpool_head *pool, int cpu)
+{
+ struct objpool_slot *slot = pool->cpu_slots[cpu];
+ /* load head snapshot, other cpus may change it */
+ u32 head = smp_load_acquire(&slot->head);
+
+ while (head != READ_ONCE(slot->last)) {
+ void *obj;
+
+ /*
+ * data visibility of 'last' and 'head' could be out of
+ * order since memory updating of 'last' and 'head' are
+ * performed in push() and pop() independently
+ *
+ * before any retrieving attempts, pop() must guarantee
+ * 'last' is behind 'head', that is to say, there must
+ * be available objects in slot, which could be ensured
+ * by condition 'last != head && last - head <= nr_objs'
+ * that is equivalent to 'last - head - 1 < nr_objs' as
+ * 'last' and 'head' are both unsigned int32
+ */
+ if (READ_ONCE(slot->last) - head - 1 >= pool->capacity) {
+ head = READ_ONCE(slot->head);
+ continue;
+ }
+
+ /* obj must be retrieved before moving forward head */
+ obj = READ_ONCE(slot->entries[head & slot->mask]);
+
+ /* move head forward to mark it's consumption */
+ if (try_cmpxchg_release(&slot->head, &head, head + 1))
+ return obj;
+ }
+
+ return NULL;
+}
+
+/* allocate an object from object pool */
+static void *objpool_pop(struct objpool_head *pool)
+{
+ void *obj = NULL;
+ unsigned long flags;
+ int i, cpu;
+
+ /* disable local irq to avoid preemption & interruption */
+ raw_local_irq_save(flags);
+
+ cpu = raw_smp_processor_id();
+ for (i = 0; i < num_possible_cpus(); i++) {
+ obj = objpool_try_get_slot(pool, cpu);
+ if (obj)
+ break;
+ cpu = cpumask_next_wrap(cpu, cpu_possible_mask, -1, 1);
+ }
+ raw_local_irq_restore(flags);
+
+ return obj;
+}
+
+/* release whole objpool forcely */
+static void objpool_free(struct objpool_head *pool)
+{
+ if (!pool->cpu_slots)
+ return;
+
+ /* release percpu slots */
+ objpool_fini_percpu_slots(pool);
+}
+
+static struct objpool_head ptr_pool;
+static int nr_objs = 512;
+static int nr_test = 5120000;
+static atomic_t nthreads;
+static struct completion wait;
+static struct page_frag_cache test_frag;
+
+module_param(nr_test, int, 0600);
+MODULE_PARM_DESC(nr_test, "number of iterations to test");
+
+static int page_frag_pop_thread(void *arg)
+{
+ struct objpool_head *pool = arg;
+ int nr = nr_test;
+
+ pr_info("page_frag pop test thread begins on cpu %d\n",
+ smp_processor_id());
+
+ while (nr > 0) {
+ void *obj = objpool_pop(pool);
+
+ if (obj) {
+ nr--;
+ page_frag_free(obj);
+ } else {
+ cond_resched();
+ }
+ }
+
+ if (atomic_dec_and_test(&nthreads))
+ complete(&wait);
+
+ pr_info("page_frag pop test thread exits on cpu %d\n",
+ smp_processor_id());
+
+ return 0;
+}
+
+static int page_frag_push_thread(void *arg)
+{
+ struct objpool_head *pool = arg;
+ int nr = nr_test;
+
+ pr_info("page_frag push test thread begins on cpu %d\n",
+ smp_processor_id());
+
+ while (nr > 0) {
+ unsigned int size = get_random_u32();
+ void *va;
+ int ret;
+
+ size = clamp(size, 4U, 4096U);
+ va = page_frag_alloc(&test_frag, size, GFP_KERNEL);
+ if (!va)
+ continue;
+
+ ret = objpool_push(va, pool);
+ if (ret) {
+ page_frag_free(va);
+ cond_resched();
+ } else {
+ nr--;
+ }
+ }
+
+ pr_info("page_frag push test thread exits on cpu %d\n",
+ smp_processor_id());
+
+ if (atomic_dec_and_test(&nthreads))
+ complete(&wait);
+
+ return 0;
+}
+
+static int __init page_frag_test_init(void)
+{
+ struct task_struct *tsk_push, *tsk_pop;
+ ktime_t start;
+ u64 duration;
+ int ret;
+
+ test_frag.va = NULL;
+ atomic_set(&nthreads, 2);
+ init_completion(&wait);
+
+ ret = objpool_init(&ptr_pool, nr_objs, GFP_KERNEL);
+ if (ret)
+ return ret;
+
+ tsk_push = kthread_create_on_cpu(page_frag_push_thread, &ptr_pool,
+ cpumask_first(cpu_online_mask),
+ "page_frag_push");
+ if (IS_ERR(tsk_push))
+ return PTR_ERR(tsk_push);
+
+ tsk_pop = kthread_create(page_frag_pop_thread, &ptr_pool,
+ "page_frag_pop");
+ if (IS_ERR(tsk_pop)) {
+ kthread_stop(tsk_push);
+ return PTR_ERR(tsk_pop);
+ }
+
+ start = ktime_get();
+ wake_up_process(tsk_push);
+ wake_up_process(tsk_pop);
+
+ pr_info("waiting for test to complete\n");
+ wait_for_completion(&wait);
+
+ duration = (u64)ktime_us_delta(ktime_get(), start);
+ pr_info("%d of iterations took: %lluus\n", nr_test, duration);
+
+ objpool_free(&ptr_pool);
+ page_frag_cache_drain(&test_frag);
+
+ return -EAGAIN;
+}
+
+static void __exit page_frag_test_exit(void)
+{
+}
+
+module_init(page_frag_test_init);
+module_exit(page_frag_test_exit);
+
+MODULE_LICENSE("GPL");
--
2.33.0
