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Subject[PATCH v2] mm: cma: support sysfs
Date
Since CMA is getting used more widely, it's more important to
keep monitoring CMA statistics for system health since it's
directly related to user experience.

This patch introduces sysfs for the CMA and exposes stats below
to keep monitor for telemetric in the system.

* the number of CMA page allocation attempts
* the number of CMA page allocation failures

With those per-CMA statistics, we could know how CMA allocadtion
failure rate for each usecases.

e.g.)
/sys/kernel/mm/cma/WIFI/cma_alloc_pages_[attempt|fail]
/sys/kernel/mm/cma/SENSOR/cma_alloc_pages_[attempt|fail]
/sys/kernel/mm/cma/BLUETOOTH/cma_alloc_pages_[attempt|fail]

Signed-off-by: Minchan Kim <minchan@kernel.org>
---

From v1 - https://lore.kernel.org/linux-mm/20210203155001.4121868-1-minchan@kernel.org/
* fix sysfs build and refactoring - willy
* rename and drop some attributes - jhubbard

Documentation/ABI/testing/sysfs-kernel-mm-cma | 25 ++++
mm/Kconfig | 7 ++
mm/Makefile | 1 +
mm/cma.c | 6 +-
mm/cma.h | 18 +++
mm/cma_sysfs.c | 114 ++++++++++++++++++
6 files changed, 170 insertions(+), 1 deletion(-)
create mode 100644 Documentation/ABI/testing/sysfs-kernel-mm-cma
create mode 100644 mm/cma_sysfs.c

diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-cma b/Documentation/ABI/testing/sysfs-kernel-mm-cma
new file mode 100644
index 000000000000..68bdcc8c7681
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-kernel-mm-cma
@@ -0,0 +1,25 @@
+What: /sys/kernel/mm/cma/
+Date: Feb 2021
+Contact: Minchan Kim <minchan@kernel.org>
+Description:
+ /sys/kernel/mm/cma/ contains a number of subdirectories by
+ cma-heap name. The subdirectory contains a number of files
+ to represent cma allocation statistics.
+
+ There are number of files under
+ /sys/kernel/mm/cma/<cma-heap-name> directory
+
+ - cma_alloc_pages_attempt
+ - cma_alloc_pages_fail
+
+What: /sys/kernel/mm/cma/<cma-heap-name>/cma_alloc_pages_attempt
+Date: Feb 2021
+Contact: Minchan Kim <minchan@kernel.org>
+Description:
+ the number of pages CMA API tried to allocate
+
+What: /sys/kernel/mm/cma/<cma-heap-name>/cma_alloc_pages_fail
+Date: Feb 2021
+Contact: Minchan Kim <minchan@kernel.org>
+Description:
+ the number of pages CMA API failed to allocate
diff --git a/mm/Kconfig b/mm/Kconfig
index ec35bf406439..ad7e9c065657 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -513,6 +513,13 @@ config CMA_DEBUGFS
help
Turns on the DebugFS interface for CMA.

+config CMA_SYSFS
+ bool "CMA information through sysfs interface"
+ depends on CMA && SYSFS
+ help
+ This option exposes some sysfs attributes to get information
+ from CMA.
+
config CMA_AREAS
int "Maximum count of the CMA areas"
depends on CMA
diff --git a/mm/Makefile b/mm/Makefile
index b2a564eec27f..0ae764e5b1a8 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -109,6 +109,7 @@ obj-$(CONFIG_CMA) += cma.o
obj-$(CONFIG_MEMORY_BALLOON) += balloon_compaction.o
obj-$(CONFIG_PAGE_EXTENSION) += page_ext.o
obj-$(CONFIG_CMA_DEBUGFS) += cma_debug.o
+obj-$(CONFIG_CMA_SYSFS) += cma_sysfs.o
obj-$(CONFIG_USERFAULTFD) += userfaultfd.o
obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o
obj-$(CONFIG_DEBUG_PAGE_REF) += debug_page_ref.o
diff --git a/mm/cma.c b/mm/cma.c
index 23d4a97c834a..0611202d6e7d 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -447,9 +447,10 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
offset = cma_bitmap_aligned_offset(cma, align);
bitmap_maxno = cma_bitmap_maxno(cma);
bitmap_count = cma_bitmap_pages_to_bits(cma, count);
+ cma_sysfs_alloc_count(cma, count);

if (bitmap_count > bitmap_maxno)
- return NULL;
+ goto out;

for (;;) {
mutex_lock(&cma->lock);
@@ -504,6 +505,9 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
__func__, count, ret);
cma_debug_show_areas(cma);
}
+out:
+ if (!page)
+ cma_sysfs_fail(cma, count);

pr_debug("%s(): returned %p\n", __func__, page);
return page;
diff --git a/mm/cma.h b/mm/cma.h
index 42ae082cb067..49a8ceddd9e8 100644
--- a/mm/cma.h
+++ b/mm/cma.h
@@ -3,6 +3,14 @@
#define __MM_CMA_H__

#include <linux/debugfs.h>
+#include <linux/kobject.h>
+
+struct cma_stat {
+ spinlock_t lock;
+ unsigned long pages_attempt; /* the number of CMA page allocation attempts */
+ unsigned long pages_fail; /* the number of CMA page allocation failures */
+ struct kobject kobj;
+};

struct cma {
unsigned long base_pfn;
@@ -16,6 +24,9 @@ struct cma {
struct debugfs_u32_array dfs_bitmap;
#endif
char name[CMA_MAX_NAME];
+#ifdef CONFIG_CMA_SYSFS
+ struct cma_stat *stat;
+#endif
};

extern struct cma cma_areas[MAX_CMA_AREAS];
@@ -26,4 +37,11 @@ static inline unsigned long cma_bitmap_maxno(struct cma *cma)
return cma->count >> cma->order_per_bit;
}

+#ifdef CONFIG_CMA_SYSFS
+void cma_sysfs_alloc_count(struct cma *cma, size_t count);
+void cma_sysfs_fail(struct cma *cma, size_t count);
+#else
+static inline void cma_sysfs_alloc_count(struct cma *cma, size_t count) {};
+static inline void cma_sysfs_fail(struct cma *cma, size_t count) {};
+#endif
#endif
diff --git a/mm/cma_sysfs.c b/mm/cma_sysfs.c
new file mode 100644
index 000000000000..1f6b9f785825
--- /dev/null
+++ b/mm/cma_sysfs.c
@@ -0,0 +1,114 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * CMA SysFS Interface
+ *
+ * Copyright (c) 2021 Minchan Kim <minchan@kernel.org>
+ */
+
+#include <linux/cma.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+
+#include "cma.h"
+
+static struct cma_stat *cma_stats;
+
+void cma_sysfs_alloc_count(struct cma *cma, size_t count)
+{
+ spin_lock(&cma->stat->lock);
+ cma->stat->pages_attempt += count;
+ spin_unlock(&cma->stat->lock);
+}
+
+void cma_sysfs_fail(struct cma *cma, size_t count)
+{
+ spin_lock(&cma->stat->lock);
+ cma->stat->pages_fail += count;
+ spin_unlock(&cma->stat->lock);
+}
+
+#define CMA_ATTR_RO(_name) \
+ static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
+
+static struct kobject *cma_kobj;
+
+static ssize_t cma_alloc_pages_attempt_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ struct cma_stat *stat = container_of(kobj, struct cma_stat, kobj);
+
+ return sysfs_emit(buf, "%lu\n", stat->pages_attempt);
+}
+CMA_ATTR_RO(cma_alloc_pages_attempt);
+
+static ssize_t cma_alloc_pages_fail_show(struct kobject *kobj,
+ struct kobj_attribute *attr, char *buf)
+{
+ struct cma_stat *stat = container_of(kobj, struct cma_stat, kobj);
+
+ return sysfs_emit(buf, "%lu\n", stat->pages_fail);
+}
+CMA_ATTR_RO(cma_alloc_pages_fail);
+
+static void cma_kobj_release(struct kobject *kobj)
+{
+ struct cma_stat *stat = container_of(kobj, struct cma_stat, kobj);
+
+ kfree(stat);
+}
+
+static struct attribute *cma_attrs[] = {
+ &cma_alloc_pages_attempt_attr.attr,
+ &cma_alloc_pages_fail_attr.attr,
+ NULL,
+};
+ATTRIBUTE_GROUPS(cma);
+
+static struct kobj_type cma_ktype = {
+ .release = cma_kobj_release,
+ .sysfs_ops = &kobj_sysfs_ops,
+ .default_groups = cma_groups
+};
+
+static int __init cma_sysfs_init(void)
+{
+ int i = 0;
+ struct cma *cma;
+
+ cma_kobj = kobject_create_and_add("cma", mm_kobj);
+ if (!cma_kobj) {
+ pr_err("failed to create cma kobject\n");
+ return -ENOMEM;
+ }
+
+ cma_stats = kzalloc(array_size(sizeof(struct cma_stat),
+ cma_area_count), GFP_KERNEL);
+ if (!cma_stats) {
+ pr_err("failed to create cma_stats\n");
+ goto out;
+ }
+
+ do {
+ cma = &cma_areas[i];
+ cma->stat = &cma_stats[i];
+ spin_lock_init(&cma->stat->lock);
+ if (kobject_init_and_add(&cma->stat->kobj, &cma_ktype,
+ cma_kobj, "%s", cma->name)) {
+ kobject_put(&cma->stat->kobj);
+ goto out;
+ }
+ } while (++i < cma_area_count)
+
+ return 0;
+out:
+ while (--i >= 0) {
+ cma = &cma_areas[i];
+ kobject_put(&cma->stat->kobj);
+ }
+
+ kfree(cma_stats);
+ kobject_put(cma_kobj);
+
+ return -ENOMEM;
+}
+subsys_initcall(cma_sysfs_init);
--
2.30.0.478.g8a0d178c01-goog
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