[PATCH v4] mm: cma: support sysfs

[PATCH v4] mm: cma: support sysfs

[Minchan Kim]

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 statistics for CMA, in order to provide
some basic monitoring of the CMA allocator.

 * the number of CMA page successful allocations
 * the number of CMA page allocation failures

These two values allow the user to calcuate the allocation
failure rate for each CMA area.

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

The cma_stat was intentionally allocated by dynamic allocation
to harmonize with kobject lifetime management.
https://lore.kernel.org/linux-mm/YCOAmXqt6dZkCQYs@kroah.com/

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
From v3 - https://lore.kernel.org/linux-mm/20210303205053.2906924-1-minchan@kernel.org/
 * fix ZERO_OR_NULL_PTR - kernel test robot
 * remove prefix cma - david@
 * resolve conflict with vmstat cma in mmotm - akpm@
 * rename stat name with success|fail

From v2 - https://lore.kernel.org/linux-mm/20210208180142.2765456-1-minchan@kernel.org/
 * sysfs doc and description modification - jhubbard

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                                      |   7 +-
 mm/cma.h                                      |  20 ++++
 mm/cma_sysfs.c                                | 110 ++++++++++++++++++
 6 files changed, 168 insertions(+), 2 deletions(-)
 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..02b2bb60c296
--- /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 subdirectory for each CMA
+		heap name (also sometimes called CMA areas).
+
+		Each CMA heap subdirectory (that is, each
+		/sys/kernel/mm/cma/<cma-heap-name> directory) contains the
+		following items:
+
+			alloc_pages_success
+			alloc_pages_fail
+
+What:		/sys/kernel/mm/cma/<cma-heap-name>/alloc_pages_success
+Date:		Feb 2021
+Contact:	Minchan Kim <minchan@kernel.org>
+Description:
+		the number of pages CMA API succeeded to allocate
+
+What:		/sys/kernel/mm/cma/<cma-heap-name>/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 24c045b24b95..febb7e8e24de 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 72227b24a616..56968b23ed7a 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 908f04775686..ac050359faae 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -507,10 +507,13 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
 
 	pr_debug("%s(): returned %p\n", __func__, page);
 out:
-	if (page)
+	if (page) {
 		count_vm_event(CMA_ALLOC_SUCCESS);
-	else
+		cma_sysfs_alloc_pages_count(cma, count);
+	} else {
 		count_vm_event(CMA_ALLOC_FAIL);
+		cma_sysfs_fail_pages_count(cma, count);
+	}
 
 	return page;
 }
diff --git a/mm/cma.h b/mm/cma.h
index 42ae082cb067..95d1aa2d808a 100644
--- a/mm/cma.h
+++ b/mm/cma.h
@@ -3,6 +3,16 @@
 #define __MM_CMA_H__
 
 #include <linux/debugfs.h>
+#include <linux/kobject.h>
+
+struct cma_stat {
+	spinlock_t lock;
+	/* the number of CMA page successful allocations */
+	unsigned long nr_pages_succeeded;
+	/* the number of CMA page allocation failures */
+	unsigned long nr_pages_failed;
+	struct kobject kobj;
+};
 
 struct cma {
 	unsigned long   base_pfn;
@@ -16,6 +26,9 @@ 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 +39,11 @@ 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_pages_count(struct cma *cma, size_t count);
+void cma_sysfs_fail_pages_count(struct cma *cma, size_t count);
+#else
+static inline void cma_sysfs_alloc_pages_count(struct cma *cma, size_t count) {};
+static inline void cma_sysfs_fail_pages_count(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..3134b2b3a96d
--- /dev/null
+++ b/mm/cma_sysfs.c
@@ -0,0 +1,110 @@
+// 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_pages_count(struct cma *cma, size_t count)
+{
+	spin_lock(&cma->stat->lock);
+	cma->stat->nr_pages_succeeded += count;
+	spin_unlock(&cma->stat->lock);
+}
+
+void cma_sysfs_fail_pages_count(struct cma *cma, size_t count)
+{
+	spin_lock(&cma->stat->lock);
+	cma->stat->nr_pages_failed += 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 alloc_pages_success_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->nr_pages_succeeded);
+}
+CMA_ATTR_RO(alloc_pages_success);
+
+static ssize_t 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->nr_pages_failed);
+}
+CMA_ATTR_RO(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[] = {
+	&alloc_pages_success_attr.attr,
+	&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)
+		return -ENOMEM;
+
+	cma_stats = kmalloc_array(cma_area_count, sizeof(struct cma_stat),
+				GFP_KERNEL|__GFP_ZERO);
+	if (ZERO_OR_NULL_PTR(cma_stats))
+		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);
-- 
2.30.1.766.gb4fecdf3b7-goog

Re: [PATCH v4] mm: cma: support sysfs

[Dmitry Osipenko]

09.03.2021 09:23, Minchan Kim пишет:
> 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 statistics for CMA, in order to provide
> some basic monitoring of the CMA allocator.
> 
>  * the number of CMA page successful allocations
>  * the number of CMA page allocation failures
> 
> These two values allow the user to calcuate the allocation
> failure rate for each CMA area.
> 
> e.g.)
>   /sys/kernel/mm/cma/WIFI/alloc_pages_[success|fail]
>   /sys/kernel/mm/cma/SENSOR/alloc_pages_[success|fail]
>   /sys/kernel/mm/cma/BLUETOOTH/alloc_pages_[success|fail]
> 
> The cma_stat was intentionally allocated by dynamic allocation
> to harmonize with kobject lifetime management.
> https://lore.kernel.org/linux-mm/YCOAmXqt6dZkCQYs@kroah.com/
> 
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Reviewed-by: John Hubbard <jhubbard@nvidia.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
> From v3 - https://lore.kernel.org/linux-mm/20210303205053.2906924-1-minchan@kernel.org/
>  * fix ZERO_OR_NULL_PTR - kernel test robot
>  * remove prefix cma - david@
>  * resolve conflict with vmstat cma in mmotm - akpm@
>  * rename stat name with success|fail
> 
> From v2 - https://lore.kernel.org/linux-mm/20210208180142.2765456-1-minchan@kernel.org/
>  * sysfs doc and description modification - jhubbard
> 
> 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                                      |   7 +-
>  mm/cma.h                                      |  20 ++++
>  mm/cma_sysfs.c                                | 110 ++++++++++++++++++
>  6 files changed, 168 insertions(+), 2 deletions(-)
>  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..02b2bb60c296
> --- /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 subdirectory for each CMA
> +		heap name (also sometimes called CMA areas).
> +
> +		Each CMA heap subdirectory (that is, each
> +		/sys/kernel/mm/cma/<cma-heap-name> directory) contains the
> +		following items:
> +
> +			alloc_pages_success
> +			alloc_pages_fail
> +
> +What:		/sys/kernel/mm/cma/<cma-heap-name>/alloc_pages_success
> +Date:		Feb 2021
> +Contact:	Minchan Kim <minchan@kernel.org>
> +Description:
> +		the number of pages CMA API succeeded to allocate
> +
> +What:		/sys/kernel/mm/cma/<cma-heap-name>/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 24c045b24b95..febb7e8e24de 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 72227b24a616..56968b23ed7a 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 908f04775686..ac050359faae 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -507,10 +507,13 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
>  
>  	pr_debug("%s(): returned %p\n", __func__, page);
>  out:
> -	if (page)
> +	if (page) {
>  		count_vm_event(CMA_ALLOC_SUCCESS);
> -	else
> +		cma_sysfs_alloc_pages_count(cma, count);
> +	} else {
>  		count_vm_event(CMA_ALLOC_FAIL);
> +		cma_sysfs_fail_pages_count(cma, count);
> +	}
>  
>  	return page;
>  }
> diff --git a/mm/cma.h b/mm/cma.h
> index 42ae082cb067..95d1aa2d808a 100644
> --- a/mm/cma.h
> +++ b/mm/cma.h
> @@ -3,6 +3,16 @@
>  #define __MM_CMA_H__
>  
>  #include <linux/debugfs.h>
> +#include <linux/kobject.h>
> +
> +struct cma_stat {
> +	spinlock_t lock;
> +	/* the number of CMA page successful allocations */
> +	unsigned long nr_pages_succeeded;
> +	/* the number of CMA page allocation failures */
> +	unsigned long nr_pages_failed;
> +	struct kobject kobj;
> +};
>  
>  struct cma {
>  	unsigned long   base_pfn;
> @@ -16,6 +26,9 @@ 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 +39,11 @@ 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_pages_count(struct cma *cma, size_t count);
> +void cma_sysfs_fail_pages_count(struct cma *cma, size_t count);
> +#else
> +static inline void cma_sysfs_alloc_pages_count(struct cma *cma, size_t count) {};
> +static inline void cma_sysfs_fail_pages_count(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..3134b2b3a96d
> --- /dev/null
> +++ b/mm/cma_sysfs.c
> @@ -0,0 +1,110 @@
> +// 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_pages_count(struct cma *cma, size_t count)
> +{
> +	spin_lock(&cma->stat->lock);
> +	cma->stat->nr_pages_succeeded += count;
> +	spin_unlock(&cma->stat->lock);
> +}
> +
> +void cma_sysfs_fail_pages_count(struct cma *cma, size_t count)
> +{
> +	spin_lock(&cma->stat->lock);
> +	cma->stat->nr_pages_failed += 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 alloc_pages_success_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->nr_pages_succeeded);
> +}
> +CMA_ATTR_RO(alloc_pages_success);
> +
> +static ssize_t 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->nr_pages_failed);
> +}
> +CMA_ATTR_RO(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[] = {
> +	&alloc_pages_success_attr.attr,
> +	&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)
> +		return -ENOMEM;
> +
> +	cma_stats = kmalloc_array(cma_area_count, sizeof(struct cma_stat),
> +				GFP_KERNEL|__GFP_ZERO);

Use kcalloc().

Code identation is wrong, please use checkpatch.

> +	if (ZERO_OR_NULL_PTR(cma_stats))
> +		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);
> 

Hi,

There is a NULL derence on ARM32 NVIDIA Tegra SoCs with CONFIG_CMA_SYSFS=y using today's next-20210319, please take a look.

[    1.185423] 8<--- cut here ---
[    1.186081] Unable to handle kernel NULL pointer dereference at virtual address 00000000
[    1.186705] pgd = (ptrval)
[    1.188130] [00000000] *pgd=00000000
[    1.190554] Internal error: Oops: 5 [#1] PREEMPT SMP THUMB2
[    1.191545] Modules linked in:
[    1.192629] CPU: 1 PID: 1 Comm: swapper/0 Tainted: G        W         5.12.0-rc3-next-20210319-00174-g89b3b421dd2b #7142
[    1.193540] Hardware name: NVIDIA Tegra SoC (Flattened Device Tree)
[    1.194613] PC is at _raw_spin_lock+0x1a/0x48
[    1.200352] LR is at cma_sysfs_alloc_pages_count+0x13/0x24
[    1.200821] pc : [<c0a2d832>]    lr : [<c027762f>]    psr: 00000033
[    1.201269] sp : c1547e48  ip : f0000080  fp : 0000c800
[    1.201580] r10: c13bd178  r9 : 00000040  r8 : 00000040
[    1.201972] r7 : 00000000  r6 : c13bd168  r5 : 00000040  r4 : c13bd168
[    1.202418] r3 : c1546000  r2 : 00000001  r1 : 00000040  r0 : 00000000
[    1.203014] Flags: nzcv  IRQs on  FIQs on  Mode SVC_32  ISA Thumb  Segment none
[    1.203488] Control: 50c5387d  Table: 0000406a  DAC: 00000051
[    1.203988] Register r0 information: NULL pointer
[    1.204868] Register r1 information: non-paged memory
[    1.205233] Register r2 information: non-paged memory
[    1.205563] Register r3 information: non-slab/vmalloc memory
[    1.206213] Register r4 information: non-slab/vmalloc memory
[    1.206578] Register r5 information: non-paged memory
[    1.206929] Register r6 information: non-slab/vmalloc memory
[    1.207278] Register r7 information: NULL pointer
[    1.207594] Register r8 information: non-paged memory
[    1.207968] Register r9 information: non-paged memory
[    1.208291] Register r10 information: non-slab/vmalloc memory
[    1.208648] Register r11 information: non-paged memory
[    1.209002] Register r12 information: non-paged memory
[    1.209407] Process swapper/0 (pid: 1, stack limit = 0x(ptrval))
[    1.209956] Stack: (0xc1547e48 to 0xc1548000)
[    1.211102] 7e40:                   c1199e24 00033800 efe35000 c027706f 0000003f 00000000
[    1.211999] 7e60: 00000040 0000003f 00000000 00000040 00000cc0 00000000 00000006 00000000
[    1.212855] 7e80: c1547ed8 00040000 c1141780 00000001 00000000 c1547ed8 00000647 00000040
[    1.213768] 7ea0: c138c000 c01112ab c0fed0d8 c1141780 c1546000 00000001 c1140d24 00000000
[    1.214648] 7ec0: c1140d44 c1104af9 c1104a7f 00000001 00000000 00000cc0 00000000 e29968ad
[    1.215578] 7ee0: c161a077 c1546000 c136d940 c1104a7f ffffe000 c0101d69 c161a077 c161a098
[    1.216564] 7f00: c1058490 c0138345 c10566cc c0ef58b8 c11003d1 c1546000 00000000 00000002
[    1.217357] 7f20: 00000002 c0f10280 c0efe3e4 c0efe398 c11003d1 c161a074 c161a077 e29968ad
[    1.218212] 7f40: c1140d40 e29968ad c161a000 c118d304 00000003 c11003d1 c161a000 c1140d24
[    1.219164] 7f60: 0000017e c1101141 00000002 00000002 00000000 c11003d1 c0a27fc5 c10566cc
[    1.220015] 7f80: c1547f98 00000000 c0a27fc5 00000000 00000000 00000000 00000000 00000000
[    1.220863] 7fa0: 00000000 c0a27fd1 00000000 c0100155 00000000 00000000 00000000 00000000
[    1.221713] 7fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
[    1.222584] 7fe0: 00000000 00000000 00000000 00000000 00000013 00000000 00000000 00000000
[    1.225038] [<c0a2d832>] (_raw_spin_lock) from [<c027762f>] (cma_sysfs_alloc_pages_count+0x13/0x24)
[    1.226190] [<c027762f>] (cma_sysfs_alloc_pages_count) from [<c027706f>] (cma_alloc+0x153/0x274)
[    1.226720] [<c027706f>] (cma_alloc) from [<c01112ab>] (__alloc_from_contiguous+0x37/0x8c)
[    1.227272] [<c01112ab>] (__alloc_from_contiguous) from [<c1104af9>] (atomic_pool_init+0x7b/0x126)
[    1.233596] [<c1104af9>] (atomic_pool_init) from [<c0101d69>] (do_one_initcall+0x45/0x1e4)
[    1.234188] [<c0101d69>] (do_one_initcall) from [<c1101141>] (kernel_init_freeable+0x157/0x1a6)
[    1.234741] [<c1101141>] (kernel_init_freeable) from [<c0a27fd1>] (kernel_init+0xd/0xe0)
[    1.235289] [<c0a27fd1>] (kernel_init) from [<c0100155>] (ret_from_fork+0x11/0x1c)

Re: [PATCH v4] mm: cma: support sysfs

[Dmitry Osipenko]

19.03.2021 15:44, Dmitry Osipenko пишет:
...
>>  #include <linux/debugfs.h>
>> +#include <linux/kobject.h>
>> +
>> +struct cma_stat {
>> +	spinlock_t lock;
>> +	/* the number of CMA page successful allocations */
>> +	unsigned long nr_pages_succeeded;
>> +	/* the number of CMA page allocation failures */
>> +	unsigned long nr_pages_failed;
>> +	struct kobject kobj;
>> +};
>>  
>>  struct cma {
>>  	unsigned long   base_pfn;
>> @@ -16,6 +26,9 @@ struct cma {
>>  	struct debugfs_u32_array dfs_bitmap;
>>  #endif
>>  	char name[CMA_MAX_NAME];
>> +#ifdef CONFIG_CMA_SYSFS
>> +	struct cma_stat	*stat;
>> +#endif

What is the point of allocating stat dynamically?

...
>> +void cma_sysfs_alloc_pages_count(struct cma *cma, size_t count)
>> +{
>> +	spin_lock(&cma->stat->lock);
>> +	cma->stat->nr_pages_succeeded += count;
>> +	spin_unlock(&cma->stat->lock);
>> +}
>> +
>> +void cma_sysfs_fail_pages_count(struct cma *cma, size_t count)
>> +{
>> +	spin_lock(&cma->stat->lock);
>> +	cma->stat->nr_pages_failed += count;
>> +	spin_unlock(&cma->stat->lock);
>> +}

You could use atomic increment and then locking isn't needed.

Re: [PATCH v4] mm: cma: support sysfs

[Greg Kroah-Hartman]

On Fri, Mar 19, 2021 at 04:39:41PM +0300, Dmitry Osipenko wrote:
> 19.03.2021 15:44, Dmitry Osipenko пишет:
> ...
> >>  #include <linux/debugfs.h>
> >> +#include <linux/kobject.h>
> >> +
> >> +struct cma_stat {
> >> +	spinlock_t lock;
> >> +	/* the number of CMA page successful allocations */
> >> +	unsigned long nr_pages_succeeded;
> >> +	/* the number of CMA page allocation failures */
> >> +	unsigned long nr_pages_failed;
> >> +	struct kobject kobj;
> >> +};
> >>  
> >>  struct cma {
> >>  	unsigned long   base_pfn;
> >> @@ -16,6 +26,9 @@ struct cma {
> >>  	struct debugfs_u32_array dfs_bitmap;
> >>  #endif
> >>  	char name[CMA_MAX_NAME];
> >> +#ifdef CONFIG_CMA_SYSFS
> >> +	struct cma_stat	*stat;
> >> +#endif
> 
> What is the point of allocating stat dynamically?

Because static kobjects make me cry.

Re: [PATCH v4] mm: cma: support sysfs

[Dmitry Osipenko]

19.03.2021 16:42, Greg Kroah-Hartman пишет:
> On Fri, Mar 19, 2021 at 04:39:41PM +0300, Dmitry Osipenko wrote:
>> 19.03.2021 15:44, Dmitry Osipenko пишет:
>> ...
>>>>  #include <linux/debugfs.h>
>>>> +#include <linux/kobject.h>
>>>> +
>>>> +struct cma_stat {
>>>> +	spinlock_t lock;
>>>> +	/* the number of CMA page successful allocations */
>>>> +	unsigned long nr_pages_succeeded;
>>>> +	/* the number of CMA page allocation failures */
>>>> +	unsigned long nr_pages_failed;
>>>> +	struct kobject kobj;
>>>> +};
>>>>  
>>>>  struct cma {
>>>>  	unsigned long   base_pfn;
>>>> @@ -16,6 +26,9 @@ struct cma {
>>>>  	struct debugfs_u32_array dfs_bitmap;
>>>>  #endif
>>>>  	char name[CMA_MAX_NAME];
>>>> +#ifdef CONFIG_CMA_SYSFS
>>>> +	struct cma_stat	*stat;
>>>> +#endif
>>
>> What is the point of allocating stat dynamically?
> 
> Because static kobjects make me cry.
> 

I meant that it's already a part of struct cma, it looks like the stat
could be embedded into struct cma and then kobj could be initialized
separately.

Re: [PATCH v4] mm: cma: support sysfs

[Greg Kroah-Hartman]

On Fri, Mar 19, 2021 at 04:45:21PM +0300, Dmitry Osipenko wrote:
> 19.03.2021 16:42, Greg Kroah-Hartman пишет:
> > On Fri, Mar 19, 2021 at 04:39:41PM +0300, Dmitry Osipenko wrote:
> >> 19.03.2021 15:44, Dmitry Osipenko пишет:
> >> ...
> >>>>  #include <linux/debugfs.h>
> >>>> +#include <linux/kobject.h>
> >>>> +
> >>>> +struct cma_stat {
> >>>> +	spinlock_t lock;
> >>>> +	/* the number of CMA page successful allocations */
> >>>> +	unsigned long nr_pages_succeeded;
> >>>> +	/* the number of CMA page allocation failures */
> >>>> +	unsigned long nr_pages_failed;
> >>>> +	struct kobject kobj;
> >>>> +};
> >>>>  
> >>>>  struct cma {
> >>>>  	unsigned long   base_pfn;
> >>>> @@ -16,6 +26,9 @@ struct cma {
> >>>>  	struct debugfs_u32_array dfs_bitmap;
> >>>>  #endif
> >>>>  	char name[CMA_MAX_NAME];
> >>>> +#ifdef CONFIG_CMA_SYSFS
> >>>> +	struct cma_stat	*stat;
> >>>> +#endif
> >>
> >> What is the point of allocating stat dynamically?
> > 
> > Because static kobjects make me cry.
> > 
> 
> I meant that it's already a part of struct cma, it looks like the stat
> could be embedded into struct cma and then kobj could be initialized
> separately.

But that structure is statically allocated, so it can not be.  This has
been discussed in the past threads for when this was reviewed if you are
curious :)

thanks,

greg k-h

Re: [PATCH v4] mm: cma: support sysfs

[Dmitry Osipenko]

19.03.2021 16:47, Greg Kroah-Hartman пишет:
> On Fri, Mar 19, 2021 at 04:45:21PM +0300, Dmitry Osipenko wrote:
>> 19.03.2021 16:42, Greg Kroah-Hartman пишет:
>>> On Fri, Mar 19, 2021 at 04:39:41PM +0300, Dmitry Osipenko wrote:
>>>> 19.03.2021 15:44, Dmitry Osipenko пишет:
>>>> ...
>>>>>>  #include <linux/debugfs.h>
>>>>>> +#include <linux/kobject.h>
>>>>>> +
>>>>>> +struct cma_stat {
>>>>>> +	spinlock_t lock;
>>>>>> +	/* the number of CMA page successful allocations */
>>>>>> +	unsigned long nr_pages_succeeded;
>>>>>> +	/* the number of CMA page allocation failures */
>>>>>> +	unsigned long nr_pages_failed;
>>>>>> +	struct kobject kobj;
>>>>>> +};
>>>>>>  
>>>>>>  struct cma {
>>>>>>  	unsigned long   base_pfn;
>>>>>> @@ -16,6 +26,9 @@ struct cma {
>>>>>>  	struct debugfs_u32_array dfs_bitmap;
>>>>>>  #endif
>>>>>>  	char name[CMA_MAX_NAME];
>>>>>> +#ifdef CONFIG_CMA_SYSFS
>>>>>> +	struct cma_stat	*stat;
>>>>>> +#endif
>>>>
>>>> What is the point of allocating stat dynamically?
>>>
>>> Because static kobjects make me cry.
>>>
>>
>> I meant that it's already a part of struct cma, it looks like the stat
>> could be embedded into struct cma and then kobj could be initialized
>> separately.
> 
> But that structure is statically allocated, so it can not be.  This has
> been discussed in the past threads for when this was reviewed if you are
> curious :)

Indeed, I missed that cma_areas[] is static, thank you.

Re: [PATCH v4] mm: cma: support sysfs

[Dmitry Osipenko]

19.03.2021 16:51, Dmitry Osipenko пишет:
> 19.03.2021 16:47, Greg Kroah-Hartman пишет:
>> On Fri, Mar 19, 2021 at 04:45:21PM +0300, Dmitry Osipenko wrote:
>>> 19.03.2021 16:42, Greg Kroah-Hartman пишет:
>>>> On Fri, Mar 19, 2021 at 04:39:41PM +0300, Dmitry Osipenko wrote:
>>>>> 19.03.2021 15:44, Dmitry Osipenko пишет:
>>>>> ...
>>>>>>>  #include <linux/debugfs.h>
>>>>>>> +#include <linux/kobject.h>
>>>>>>> +
>>>>>>> +struct cma_stat {
>>>>>>> +	spinlock_t lock;
>>>>>>> +	/* the number of CMA page successful allocations */
>>>>>>> +	unsigned long nr_pages_succeeded;
>>>>>>> +	/* the number of CMA page allocation failures */
>>>>>>> +	unsigned long nr_pages_failed;
>>>>>>> +	struct kobject kobj;
>>>>>>> +};
>>>>>>>  
>>>>>>>  struct cma {
>>>>>>>  	unsigned long   base_pfn;
>>>>>>> @@ -16,6 +26,9 @@ struct cma {
>>>>>>>  	struct debugfs_u32_array dfs_bitmap;
>>>>>>>  #endif
>>>>>>>  	char name[CMA_MAX_NAME];
>>>>>>> +#ifdef CONFIG_CMA_SYSFS
>>>>>>> +	struct cma_stat	*stat;
>>>>>>> +#endif
>>>>>
>>>>> What is the point of allocating stat dynamically?
>>>>
>>>> Because static kobjects make me cry.
>>>>
>>>
>>> I meant that it's already a part of struct cma, it looks like the stat
>>> could be embedded into struct cma and then kobj could be initialized
>>> separately.
>>
>> But that structure is statically allocated, so it can not be.  This has
>> been discussed in the past threads for when this was reviewed if you are
>> curious :)
> 
> Indeed, I missed that cma_areas[] is static, thank you.
> 

And in this case should be better to make only the kobj allocated
dynamically instead of the whole cma_stat.

Re: [PATCH v4] mm: cma: support sysfs

[Greg Kroah-Hartman]

On Fri, Mar 19, 2021 at 05:19:47PM +0300, Dmitry Osipenko wrote:
> 19.03.2021 16:51, Dmitry Osipenko пишет:
> > 19.03.2021 16:47, Greg Kroah-Hartman пишет:
> >> On Fri, Mar 19, 2021 at 04:45:21PM +0300, Dmitry Osipenko wrote:
> >>> 19.03.2021 16:42, Greg Kroah-Hartman пишет:
> >>>> On Fri, Mar 19, 2021 at 04:39:41PM +0300, Dmitry Osipenko wrote:
> >>>>> 19.03.2021 15:44, Dmitry Osipenko пишет:
> >>>>> ...
> >>>>>>>  #include <linux/debugfs.h>
> >>>>>>> +#include <linux/kobject.h>
> >>>>>>> +
> >>>>>>> +struct cma_stat {
> >>>>>>> +	spinlock_t lock;
> >>>>>>> +	/* the number of CMA page successful allocations */
> >>>>>>> +	unsigned long nr_pages_succeeded;
> >>>>>>> +	/* the number of CMA page allocation failures */
> >>>>>>> +	unsigned long nr_pages_failed;
> >>>>>>> +	struct kobject kobj;
> >>>>>>> +};
> >>>>>>>  
> >>>>>>>  struct cma {
> >>>>>>>  	unsigned long   base_pfn;
> >>>>>>> @@ -16,6 +26,9 @@ struct cma {
> >>>>>>>  	struct debugfs_u32_array dfs_bitmap;
> >>>>>>>  #endif
> >>>>>>>  	char name[CMA_MAX_NAME];
> >>>>>>> +#ifdef CONFIG_CMA_SYSFS
> >>>>>>> +	struct cma_stat	*stat;
> >>>>>>> +#endif
> >>>>>
> >>>>> What is the point of allocating stat dynamically?
> >>>>
> >>>> Because static kobjects make me cry.
> >>>>
> >>>
> >>> I meant that it's already a part of struct cma, it looks like the stat
> >>> could be embedded into struct cma and then kobj could be initialized
> >>> separately.
> >>
> >> But that structure is statically allocated, so it can not be.  This has
> >> been discussed in the past threads for when this was reviewed if you are
> >> curious :)
> > 
> > Indeed, I missed that cma_areas[] is static, thank you.
> > 
> 
> And in this case should be better to make only the kobj allocated
> dynamically instead of the whole cma_stat.

Why does it matter?

Re: [PATCH v4] mm: cma: support sysfs

[Dmitry Osipenko]

19.03.2021 17:27, Greg Kroah-Hartman пишет:
> On Fri, Mar 19, 2021 at 05:19:47PM +0300, Dmitry Osipenko wrote:
>> 19.03.2021 16:51, Dmitry Osipenko пишет:
>>> 19.03.2021 16:47, Greg Kroah-Hartman пишет:
>>>> On Fri, Mar 19, 2021 at 04:45:21PM +0300, Dmitry Osipenko wrote:
>>>>> 19.03.2021 16:42, Greg Kroah-Hartman пишет:
>>>>>> On Fri, Mar 19, 2021 at 04:39:41PM +0300, Dmitry Osipenko wrote:
>>>>>>> 19.03.2021 15:44, Dmitry Osipenko пишет:
>>>>>>> ...
>>>>>>>>>  #include <linux/debugfs.h>
>>>>>>>>> +#include <linux/kobject.h>
>>>>>>>>> +
>>>>>>>>> +struct cma_stat {
>>>>>>>>> +	spinlock_t lock;
>>>>>>>>> +	/* the number of CMA page successful allocations */
>>>>>>>>> +	unsigned long nr_pages_succeeded;
>>>>>>>>> +	/* the number of CMA page allocation failures */
>>>>>>>>> +	unsigned long nr_pages_failed;
>>>>>>>>> +	struct kobject kobj;
>>>>>>>>> +};
>>>>>>>>>  
>>>>>>>>>  struct cma {
>>>>>>>>>  	unsigned long   base_pfn;
>>>>>>>>> @@ -16,6 +26,9 @@ struct cma {
>>>>>>>>>  	struct debugfs_u32_array dfs_bitmap;
>>>>>>>>>  #endif
>>>>>>>>>  	char name[CMA_MAX_NAME];
>>>>>>>>> +#ifdef CONFIG_CMA_SYSFS
>>>>>>>>> +	struct cma_stat	*stat;
>>>>>>>>> +#endif
>>>>>>>
>>>>>>> What is the point of allocating stat dynamically?
>>>>>>
>>>>>> Because static kobjects make me cry.
>>>>>>
>>>>>
>>>>> I meant that it's already a part of struct cma, it looks like the stat
>>>>> could be embedded into struct cma and then kobj could be initialized
>>>>> separately.
>>>>
>>>> But that structure is statically allocated, so it can not be.  This has
>>>> been discussed in the past threads for when this was reviewed if you are
>>>> curious :)
>>>
>>> Indeed, I missed that cma_areas[] is static, thank you.
>>>
>>
>> And in this case should be better to make only the kobj allocated
>> dynamically instead of the whole cma_stat.
> 
> Why does it matter?
> 

Then initialization order won't be a problem.

Re: [PATCH v4] mm: cma: support sysfs

[Greg Kroah-Hartman]

On Fri, Mar 19, 2021 at 06:38:00PM +0300, Dmitry Osipenko wrote:
> 19.03.2021 17:27, Greg Kroah-Hartman пишет:
> > On Fri, Mar 19, 2021 at 05:19:47PM +0300, Dmitry Osipenko wrote:
> >> 19.03.2021 16:51, Dmitry Osipenko пишет:
> >>> 19.03.2021 16:47, Greg Kroah-Hartman пишет:
> >>>> On Fri, Mar 19, 2021 at 04:45:21PM +0300, Dmitry Osipenko wrote:
> >>>>> 19.03.2021 16:42, Greg Kroah-Hartman пишет:
> >>>>>> On Fri, Mar 19, 2021 at 04:39:41PM +0300, Dmitry Osipenko wrote:
> >>>>>>> 19.03.2021 15:44, Dmitry Osipenko пишет:
> >>>>>>> ...
> >>>>>>>>>  #include <linux/debugfs.h>
> >>>>>>>>> +#include <linux/kobject.h>
> >>>>>>>>> +
> >>>>>>>>> +struct cma_stat {
> >>>>>>>>> +	spinlock_t lock;
> >>>>>>>>> +	/* the number of CMA page successful allocations */
> >>>>>>>>> +	unsigned long nr_pages_succeeded;
> >>>>>>>>> +	/* the number of CMA page allocation failures */
> >>>>>>>>> +	unsigned long nr_pages_failed;
> >>>>>>>>> +	struct kobject kobj;
> >>>>>>>>> +};
> >>>>>>>>>  
> >>>>>>>>>  struct cma {
> >>>>>>>>>  	unsigned long   base_pfn;
> >>>>>>>>> @@ -16,6 +26,9 @@ struct cma {
> >>>>>>>>>  	struct debugfs_u32_array dfs_bitmap;
> >>>>>>>>>  #endif
> >>>>>>>>>  	char name[CMA_MAX_NAME];
> >>>>>>>>> +#ifdef CONFIG_CMA_SYSFS
> >>>>>>>>> +	struct cma_stat	*stat;
> >>>>>>>>> +#endif
> >>>>>>>
> >>>>>>> What is the point of allocating stat dynamically?
> >>>>>>
> >>>>>> Because static kobjects make me cry.
> >>>>>>
> >>>>>
> >>>>> I meant that it's already a part of struct cma, it looks like the stat
> >>>>> could be embedded into struct cma and then kobj could be initialized
> >>>>> separately.
> >>>>
> >>>> But that structure is statically allocated, so it can not be.  This has
> >>>> been discussed in the past threads for when this was reviewed if you are
> >>>> curious :)
> >>>
> >>> Indeed, I missed that cma_areas[] is static, thank you.
> >>>
> >>
> >> And in this case should be better to make only the kobj allocated
> >> dynamically instead of the whole cma_stat.
> > 
> > Why does it matter?
> > 
> 
> Then initialization order won't be a problem.

I don't understand the problem here, what is wrong with the patch as-is?

Also, watch out, if you only make the kobject dynamic, how are you going
to get backwards from the kobject to the values you want to send to
userspace in the show functions?

thanks,

greg k-h

Re: [PATCH v4] mm: cma: support sysfs

[Dmitry Osipenko]

19.03.2021 18:50, Greg Kroah-Hartman пишет:
>> Then initialization order won't be a problem.
> I don't understand the problem here, what is wrong with the patch as-is?

The cma->stat is NULL at the time when CMA is used on ARM because
cma->stat is initialized at the subsys level. This is the problem,
apparently.

> Also, watch out, if you only make the kobject dynamic, how are you going
> to get backwards from the kobject to the values you want to send to
> userspace in the show functions?

Still there should be a wrapper around the kobj with a back reference to
the cma entry. If you're suggesting that I should write a patch, then I
may take a look at it later on. Although, I assume that Minchan could
just correct this patch and re-push it to -next.

Re: [PATCH v4] mm: cma: support sysfs

[Minchan Kim]

On Fri, Mar 19, 2021 at 07:24:05PM +0300, Dmitry Osipenko wrote:
> 19.03.2021 18:50, Greg Kroah-Hartman пишет:
> >> Then initialization order won't be a problem.
> > I don't understand the problem here, what is wrong with the patch as-is?
> 
> The cma->stat is NULL at the time when CMA is used on ARM because
> cma->stat is initialized at the subsys level. This is the problem,
> apparently.

That's true.

> 
> > Also, watch out, if you only make the kobject dynamic, how are you going
> > to get backwards from the kobject to the values you want to send to
> > userspace in the show functions?
> 
> Still there should be a wrapper around the kobj with a back reference to
> the cma entry. If you're suggesting that I should write a patch, then I
> may take a look at it later on. Although, I assume that Minchan could
> just correct this patch and re-push it to -next.

This is ateempt to address it. Unless any objection, let me send it to
akpm.

From 29a9fb4f300b754ebf55e6182ba84127658ef504 Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Fri, 22 Jan 2021 12:31:56 -0800
Subject: [PATCH] mm: cma: support sysfs

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 statistics for CMA, in order to provide
some basic monitoring of the CMA allocator.

 * the number of CMA page successful allocations
 * the number of CMA page allocation failures

These two values allow the user to calcuate the allocation
failure rate for each CMA area.

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

The cma_stat was intentionally allocated by dynamic allocation
to harmonize with kobject lifetime management.
https://lore.kernel.org/linux-mm/YCOAmXqt6dZkCQYs@kroah.com/

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 Documentation/ABI/testing/sysfs-kernel-mm-cma |  25 ++++
 mm/Kconfig                                    |   7 ++
 mm/Makefile                                   |   1 +
 mm/cma.c                                      |   7 +-
 mm/cma.h                                      |  20 ++++
 mm/cma_sysfs.c                                | 107 ++++++++++++++++++
 6 files changed, 165 insertions(+), 2 deletions(-)
 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..02b2bb60c296
--- /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 subdirectory for each CMA
+		heap name (also sometimes called CMA areas).
+
+		Each CMA heap subdirectory (that is, each
+		/sys/kernel/mm/cma/<cma-heap-name> directory) contains the
+		following items:
+
+			alloc_pages_success
+			alloc_pages_fail
+
+What:		/sys/kernel/mm/cma/<cma-heap-name>/alloc_pages_success
+Date:		Feb 2021
+Contact:	Minchan Kim <minchan@kernel.org>
+Description:
+		the number of pages CMA API succeeded to allocate
+
+What:		/sys/kernel/mm/cma/<cma-heap-name>/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 24c045b24b95..febb7e8e24de 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 72227b24a616..56968b23ed7a 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 908f04775686..ac050359faae 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -507,10 +507,13 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
 
 	pr_debug("%s(): returned %p\n", __func__, page);
 out:
-	if (page)
+	if (page) {
 		count_vm_event(CMA_ALLOC_SUCCESS);
-	else
+		cma_sysfs_alloc_pages_count(cma, count);
+	} else {
 		count_vm_event(CMA_ALLOC_FAIL);
+		cma_sysfs_fail_pages_count(cma, count);
+	}
 
 	return page;
 }
diff --git a/mm/cma.h b/mm/cma.h
index 42ae082cb067..70fd7633fe01 100644
--- a/mm/cma.h
+++ b/mm/cma.h
@@ -3,6 +3,12 @@
 #define __MM_CMA_H__
 
 #include <linux/debugfs.h>
+#include <linux/kobject.h>
+
+struct cma_kobject {
+	struct cma *cma;
+	struct kobject kobj;
+};
 
 struct cma {
 	unsigned long   base_pfn;
@@ -16,6 +22,13 @@ struct cma {
 	struct debugfs_u32_array dfs_bitmap;
 #endif
 	char name[CMA_MAX_NAME];
+#ifdef CONFIG_CMA_SYSFS
+	/* the number of CMA page successful allocations */
+	atomic64_t nr_pages_succeeded;
+	/* the number of CMA page allocation failures */
+	atomic64_t nr_pages_failed;
+	struct cma_kobject *kobj;
+#endif
 };
 
 extern struct cma cma_areas[MAX_CMA_AREAS];
@@ -26,4 +39,11 @@ 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_pages_count(struct cma *cma, size_t count);
+void cma_sysfs_fail_pages_count(struct cma *cma, size_t count);
+#else
+static inline void cma_sysfs_alloc_pages_count(struct cma *cma, size_t count) {};
+static inline void cma_sysfs_fail_pages_count(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..ca093e9e9f64
--- /dev/null
+++ b/mm/cma_sysfs.c
@@ -0,0 +1,107 @@
+// 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"
+
+void cma_sysfs_alloc_pages_count(struct cma *cma, size_t count)
+{
+	atomic64_add(count, &cma->nr_pages_succeeded);
+}
+
+void cma_sysfs_fail_pages_count(struct cma *cma, size_t count)
+{
+	atomic64_add(count, &cma->nr_pages_failed);
+}
+
+#define CMA_ATTR_RO(_name) \
+	static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
+
+static ssize_t alloc_pages_success_show(struct kobject *kobj,
+			struct kobj_attribute *attr, char *buf)
+{
+	struct cma_kobject *cma_kobj = container_of(kobj, struct cma_kobject, kobj);
+	struct cma *cma = cma_kobj->cma;
+
+	return sysfs_emit(buf, "%llu\n", atomic64_read(&cma->nr_pages_succeeded));
+}
+CMA_ATTR_RO(alloc_pages_success);
+
+static ssize_t alloc_pages_fail_show(struct kobject *kobj,
+			struct kobj_attribute *attr, char *buf)
+{
+	struct cma_kobject *cma_kobj = container_of(kobj, struct cma_kobject, kobj);
+	struct cma *cma = cma_kobj->cma;
+
+	return sysfs_emit(buf, "%llu\n", atomic64_read(&cma->nr_pages_failed));
+}
+CMA_ATTR_RO(alloc_pages_fail);
+
+static void cma_kobj_release(struct kobject *kobj)
+{
+	struct cma_kobject *cma_kobj = container_of(kobj, struct cma_kobject, kobj);
+
+	kfree(cma_kobj);
+}
+
+static struct attribute *cma_attrs[] = {
+	&alloc_pages_success_attr.attr,
+	&alloc_pages_fail_attr.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(cma);
+
+static struct cma_kobject *cma_kobjs;
+static struct kobject *cma_kobj_root;
+
+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_root = kobject_create_and_add("cma", mm_kobj);
+	if (!cma_kobj_root)
+		return -ENOMEM;
+
+	cma_kobjs = kcalloc(cma_area_count, sizeof(struct cma_kobject),
+				GFP_KERNEL);
+	if (ZERO_OR_NULL_PTR(cma_kobjs))
+		goto out;
+
+	do {
+		cma = &cma_areas[i];
+		cma->kobj = &cma_kobjs[i];
+		cma->kobj->cma = cma;
+		if (kobject_init_and_add(&cma->kobj->kobj, &cma_ktype,
+					cma_kobj_root, "%s", cma->name)) {
+			kobject_put(&cma->kobj->kobj);
+			goto out;
+		}
+	} while (++i < cma_area_count);
+
+	return 0;
+out:
+	while (--i >= 0) {
+		cma = &cma_areas[i];
+		kobject_put(&cma->kobj->kobj);
+	}
+
+	kfree(cma_kobjs);
+	kobject_put(cma_kobj_root);
+
+	return -ENOMEM;
+}
+subsys_initcall(cma_sysfs_init);
-- 
2.31.0.rc2.261.g7f71774620-goog

Re: [PATCH v4] mm: cma: support sysfs

[Dmitry Osipenko]

19.03.2021 19:30, Minchan Kim пишет:
> On Fri, Mar 19, 2021 at 07:24:05PM +0300, Dmitry Osipenko wrote:
>> 19.03.2021 18:50, Greg Kroah-Hartman пишет:
>>>> Then initialization order won't be a problem.
>>> I don't understand the problem here, what is wrong with the patch as-is?
>>
>> The cma->stat is NULL at the time when CMA is used on ARM because
>> cma->stat is initialized at the subsys level. This is the problem,
>> apparently.
> 
> That's true.
> 
>>
>>> Also, watch out, if you only make the kobject dynamic, how are you going
>>> to get backwards from the kobject to the values you want to send to
>>> userspace in the show functions?
>>
>> Still there should be a wrapper around the kobj with a back reference to
>> the cma entry. If you're suggesting that I should write a patch, then I
>> may take a look at it later on. Although, I assume that Minchan could
>> just correct this patch and re-push it to -next.
> 
> This is ateempt to address it. Unless any objection, let me send it to
> akpm.
> 
> From 29a9fb4f300b754ebf55e6182ba84127658ef504 Mon Sep 17 00:00:00 2001
> From: Minchan Kim <minchan@kernel.org>
> Date: Fri, 22 Jan 2021 12:31:56 -0800
> Subject: [PATCH] mm: cma: support sysfs
> 
> 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 statistics for CMA, in order to provide
> some basic monitoring of the CMA allocator.
> 
>  * the number of CMA page successful allocations
>  * the number of CMA page allocation failures
> 
> These two values allow the user to calcuate the allocation
> failure rate for each CMA area.
> 
> e.g.)
>   /sys/kernel/mm/cma/WIFI/alloc_pages_[success|fail]
>   /sys/kernel/mm/cma/SENSOR/alloc_pages_[success|fail]
>   /sys/kernel/mm/cma/BLUETOOTH/alloc_pages_[success|fail]
> 
> The cma_stat was intentionally allocated by dynamic allocation
> to harmonize with kobject lifetime management.
> https://lore.kernel.org/linux-mm/YCOAmXqt6dZkCQYs@kroah.com/
> 
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>  Documentation/ABI/testing/sysfs-kernel-mm-cma |  25 ++++
>  mm/Kconfig                                    |   7 ++
>  mm/Makefile                                   |   1 +
>  mm/cma.c                                      |   7 +-
>  mm/cma.h                                      |  20 ++++
>  mm/cma_sysfs.c                                | 107 ++++++++++++++++++
>  6 files changed, 165 insertions(+), 2 deletions(-)
>  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..02b2bb60c296
> --- /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 subdirectory for each CMA
> +		heap name (also sometimes called CMA areas).
> +
> +		Each CMA heap subdirectory (that is, each
> +		/sys/kernel/mm/cma/<cma-heap-name> directory) contains the
> +		following items:
> +
> +			alloc_pages_success
> +			alloc_pages_fail
> +
> +What:		/sys/kernel/mm/cma/<cma-heap-name>/alloc_pages_success
> +Date:		Feb 2021
> +Contact:	Minchan Kim <minchan@kernel.org>
> +Description:
> +		the number of pages CMA API succeeded to allocate
> +
> +What:		/sys/kernel/mm/cma/<cma-heap-name>/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 24c045b24b95..febb7e8e24de 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 72227b24a616..56968b23ed7a 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 908f04775686..ac050359faae 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -507,10 +507,13 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
>  
>  	pr_debug("%s(): returned %p\n", __func__, page);
>  out:
> -	if (page)
> +	if (page) {
>  		count_vm_event(CMA_ALLOC_SUCCESS);
> -	else
> +		cma_sysfs_alloc_pages_count(cma, count);
> +	} else {
>  		count_vm_event(CMA_ALLOC_FAIL);
> +		cma_sysfs_fail_pages_count(cma, count);
> +	}
>  
>  	return page;
>  }
> diff --git a/mm/cma.h b/mm/cma.h
> index 42ae082cb067..70fd7633fe01 100644
> --- a/mm/cma.h
> +++ b/mm/cma.h
> @@ -3,6 +3,12 @@
>  #define __MM_CMA_H__
>  
>  #include <linux/debugfs.h>
> +#include <linux/kobject.h>
> +
> +struct cma_kobject {
> +	struct cma *cma;
> +	struct kobject kobj;
> +};
>  
>  struct cma {
>  	unsigned long   base_pfn;
> @@ -16,6 +22,13 @@ struct cma {
>  	struct debugfs_u32_array dfs_bitmap;
>  #endif
>  	char name[CMA_MAX_NAME];
> +#ifdef CONFIG_CMA_SYSFS
> +	/* the number of CMA page successful allocations */
> +	atomic64_t nr_pages_succeeded;
> +	/* the number of CMA page allocation failures */
> +	atomic64_t nr_pages_failed;
> +	struct cma_kobject *kobj;
> +#endif
>  };
>  
>  extern struct cma cma_areas[MAX_CMA_AREAS];
> @@ -26,4 +39,11 @@ 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_pages_count(struct cma *cma, size_t count);
> +void cma_sysfs_fail_pages_count(struct cma *cma, size_t count);
> +#else
> +static inline void cma_sysfs_alloc_pages_count(struct cma *cma, size_t count) {};
> +static inline void cma_sysfs_fail_pages_count(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..ca093e9e9f64
> --- /dev/null
> +++ b/mm/cma_sysfs.c
> @@ -0,0 +1,107 @@
> +// 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"
> +
> +void cma_sysfs_alloc_pages_count(struct cma *cma, size_t count)
> +{
> +	atomic64_add(count, &cma->nr_pages_succeeded);
> +}
> +
> +void cma_sysfs_fail_pages_count(struct cma *cma, size_t count)
> +{
> +	atomic64_add(count, &cma->nr_pages_failed);
> +}
> +
> +#define CMA_ATTR_RO(_name) \
> +	static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
> +
> +static ssize_t alloc_pages_success_show(struct kobject *kobj,
> +			struct kobj_attribute *attr, char *buf)

The indentations are still wrong.

CHECK: Alignment should match open parenthesis
#321: FILE: mm/cma_sysfs.c:28:
+static ssize_t alloc_pages_success_show(struct kobject *kobj,
+                       struct kobj_attribute *attr, char *buf)

> +{
> +	struct cma_kobject *cma_kobj = container_of(kobj, struct cma_kobject, kobj);
> +	struct cma *cma = cma_kobj->cma;
> +
> +	return sysfs_emit(buf, "%llu\n", atomic64_read(&cma->nr_pages_succeeded));
> +}
> +CMA_ATTR_RO(alloc_pages_success);
> +
> +static ssize_t alloc_pages_fail_show(struct kobject *kobj,
> +			struct kobj_attribute *attr, char *buf)

CHECK: Alignment should match open parenthesis
#331: FILE: mm/cma_sysfs.c:38:
+static ssize_t alloc_pages_fail_show(struct kobject *kobj,
+                       struct kobj_attribute *attr, char *buf)

> +{
> +	struct cma_kobject *cma_kobj = container_of(kobj, struct cma_kobject, kobj);
> +	struct cma *cma = cma_kobj->cma;
> +
> +	return sysfs_emit(buf, "%llu\n", atomic64_read(&cma->nr_pages_failed));
> +}
> +CMA_ATTR_RO(alloc_pages_fail);
> +
> +static void cma_kobj_release(struct kobject *kobj)
> +{
> +	struct cma_kobject *cma_kobj = container_of(kobj, struct cma_kobject, kobj);
> +
> +	kfree(cma_kobj);
> +}
> +
> +static struct attribute *cma_attrs[] = {
> +	&alloc_pages_success_attr.attr,
> +	&alloc_pages_fail_attr.attr,
> +	NULL,
> +};
> +ATTRIBUTE_GROUPS(cma);
> +
> +static struct cma_kobject *cma_kobjs;
> +static struct kobject *cma_kobj_root;
> +
> +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_root = kobject_create_and_add("cma", mm_kobj);
> +	if (!cma_kobj_root)
> +		return -ENOMEM;
> +
> +	cma_kobjs = kcalloc(cma_area_count, sizeof(struct cma_kobject),
> +				GFP_KERNEL);

CHECK: Alignment should match open parenthesis
#373: FILE: mm/cma_sysfs.c:80:
+       cma_kobjs = kcalloc(cma_area_count, sizeof(struct cma_kobject),
+                               GFP_KERNEL);


> +	if (ZERO_OR_NULL_PTR(cma_kobjs))
> +		goto out;
> +
> +	do {
> +		cma = &cma_areas[i];
> +		cma->kobj = &cma_kobjs[i];

Does cma really need are pointer to cma_kobj?

> +		cma->kobj->cma = cma;
> +		if (kobject_init_and_add(&cma->kobj->kobj, &cma_ktype,
> +					cma_kobj_root, "%s", cma->name)) {

CHECK: Alignment should match open parenthesis
#382: FILE: mm/cma_sysfs.c:89:
+               if (kobject_init_and_add(&cma->kobj->kobj, &cma_ktype,
+                                       cma_kobj_root, "%s", cma->name)) {

> +			kobject_put(&cma->kobj->kobj);
> +			goto out;
> +		}
> +	} while (++i < cma_area_count);
> +
> +	return 0;
> +out:
> +	while (--i >= 0) {
> +		cma = &cma_areas[i];
> +		kobject_put(&cma->kobj->kobj);

Should the cma->kobj be set to NULL by cma_kobj_release() if cma->kobj is really needed?

> +	}
> +
> +	kfree(cma_kobjs);
> +	kobject_put(cma_kobj_root);
> +
> +	return -ENOMEM;
> +}
> +subsys_initcall(cma_sysfs_init);
> 

Tested-by: Dmitry Osipenko <digetx@gmail.com>

Re: [PATCH v4] mm: cma: support sysfs

[Dmitry Osipenko]

19.03.2021 20:29, Dmitry Osipenko пишет:
> +void cma_sysfs_alloc_pages_count(struct cma *cma, size_t count)
> +{
> +	atomic64_add(count, &cma->nr_pages_succeeded);
> +}
> +
> +void cma_sysfs_fail_pages_count(struct cma *cma, size_t count)
> +{
> +	atomic64_add(count, &cma->nr_pages_failed);
> +}

The atomic looks good, but aren't CMA allocations already protected by
the CMA core? Do we really need to worry about racing here?

Re: [PATCH v4] mm: cma: support sysfs

[Dmitry Osipenko]

19.03.2021 20:41, Dmitry Osipenko пишет:
> 19.03.2021 20:29, Dmitry Osipenko пишет:
>> +void cma_sysfs_alloc_pages_count(struct cma *cma, size_t count)
>> +{
>> +	atomic64_add(count, &cma->nr_pages_succeeded);
>> +}
>> +
>> +void cma_sysfs_fail_pages_count(struct cma *cma, size_t count)
>> +{
>> +	atomic64_add(count, &cma->nr_pages_failed);
>> +}
> 
> The atomic looks good, but aren't CMA allocations already protected by
> the CMA core? Do we really need to worry about racing here?
> 

Although, please scratch that. I see now that these functions are called
outside of the lock.

Re: [PATCH v4] mm: cma: support sysfs

[Matthew Wilcox]

On Fri, Mar 19, 2021 at 08:29:29PM +0300, Dmitry Osipenko wrote:
> > +static ssize_t alloc_pages_success_show(struct kobject *kobj,
> > +			struct kobj_attribute *attr, char *buf)
> 
> The indentations are still wrong.
> 
> CHECK: Alignment should match open parenthesis
> #321: FILE: mm/cma_sysfs.c:28:
> +static ssize_t alloc_pages_success_show(struct kobject *kobj,
> +                       struct kobj_attribute *attr, char *buf)

This is bullshit.  Do not waste people's time with this frivolity.

Re: [PATCH v4] mm: cma: support sysfs

[Minchan Kim]

On Fri, Mar 19, 2021 at 08:29:29PM +0300, Dmitry Osipenko wrote:
> 19.03.2021 19:30, Minchan Kim пишет:
> > On Fri, Mar 19, 2021 at 07:24:05PM +0300, Dmitry Osipenko wrote:
> >> 19.03.2021 18:50, Greg Kroah-Hartman пишет:
> >>>> Then initialization order won't be a problem.
> >>> I don't understand the problem here, what is wrong with the patch as-is?
> >>
> >> The cma->stat is NULL at the time when CMA is used on ARM because
> >> cma->stat is initialized at the subsys level. This is the problem,
> >> apparently.
> > 
> > That's true.
> > 
> >>
> >>> Also, watch out, if you only make the kobject dynamic, how are you going
> >>> to get backwards from the kobject to the values you want to send to
> >>> userspace in the show functions?
> >>
> >> Still there should be a wrapper around the kobj with a back reference to
> >> the cma entry. If you're suggesting that I should write a patch, then I
> >> may take a look at it later on. Although, I assume that Minchan could
> >> just correct this patch and re-push it to -next.
> > 
> > This is ateempt to address it. Unless any objection, let me send it to
> > akpm.
> > 
> > From 29a9fb4f300b754ebf55e6182ba84127658ef504 Mon Sep 17 00:00:00 2001
> > From: Minchan Kim <minchan@kernel.org>
> > Date: Fri, 22 Jan 2021 12:31:56 -0800
> > Subject: [PATCH] mm: cma: support sysfs
> > 
> > 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 statistics for CMA, in order to provide
> > some basic monitoring of the CMA allocator.
> > 
> >  * the number of CMA page successful allocations
> >  * the number of CMA page allocation failures
> > 
> > These two values allow the user to calcuate the allocation
> > failure rate for each CMA area.
> > 
> > e.g.)
> >   /sys/kernel/mm/cma/WIFI/alloc_pages_[success|fail]
> >   /sys/kernel/mm/cma/SENSOR/alloc_pages_[success|fail]
> >   /sys/kernel/mm/cma/BLUETOOTH/alloc_pages_[success|fail]
> > 
> > The cma_stat was intentionally allocated by dynamic allocation
> > to harmonize with kobject lifetime management.
> > https://lore.kernel.org/linux-mm/YCOAmXqt6dZkCQYs@kroah.com/
> > 
> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > ---
> >  Documentation/ABI/testing/sysfs-kernel-mm-cma |  25 ++++
> >  mm/Kconfig                                    |   7 ++
> >  mm/Makefile                                   |   1 +
> >  mm/cma.c                                      |   7 +-
> >  mm/cma.h                                      |  20 ++++
> >  mm/cma_sysfs.c                                | 107 ++++++++++++++++++
> >  6 files changed, 165 insertions(+), 2 deletions(-)
> >  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..02b2bb60c296
> > --- /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 subdirectory for each CMA
> > +		heap name (also sometimes called CMA areas).
> > +
> > +		Each CMA heap subdirectory (that is, each
> > +		/sys/kernel/mm/cma/<cma-heap-name> directory) contains the
> > +		following items:
> > +
> > +			alloc_pages_success
> > +			alloc_pages_fail
> > +
> > +What:		/sys/kernel/mm/cma/<cma-heap-name>/alloc_pages_success
> > +Date:		Feb 2021
> > +Contact:	Minchan Kim <minchan@kernel.org>
> > +Description:
> > +		the number of pages CMA API succeeded to allocate
> > +
> > +What:		/sys/kernel/mm/cma/<cma-heap-name>/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 24c045b24b95..febb7e8e24de 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 72227b24a616..56968b23ed7a 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 908f04775686..ac050359faae 100644
> > --- a/mm/cma.c
> > +++ b/mm/cma.c
> > @@ -507,10 +507,13 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
> >  
> >  	pr_debug("%s(): returned %p\n", __func__, page);
> >  out:
> > -	if (page)
> > +	if (page) {
> >  		count_vm_event(CMA_ALLOC_SUCCESS);
> > -	else
> > +		cma_sysfs_alloc_pages_count(cma, count);
> > +	} else {
> >  		count_vm_event(CMA_ALLOC_FAIL);
> > +		cma_sysfs_fail_pages_count(cma, count);
> > +	}
> >  
> >  	return page;
> >  }
> > diff --git a/mm/cma.h b/mm/cma.h
> > index 42ae082cb067..70fd7633fe01 100644
> > --- a/mm/cma.h
> > +++ b/mm/cma.h
> > @@ -3,6 +3,12 @@
> >  #define __MM_CMA_H__
> >  
> >  #include <linux/debugfs.h>
> > +#include <linux/kobject.h>
> > +
> > +struct cma_kobject {
> > +	struct cma *cma;
> > +	struct kobject kobj;
> > +};
> >  
> >  struct cma {
> >  	unsigned long   base_pfn;
> > @@ -16,6 +22,13 @@ struct cma {
> >  	struct debugfs_u32_array dfs_bitmap;
> >  #endif
> >  	char name[CMA_MAX_NAME];
> > +#ifdef CONFIG_CMA_SYSFS
> > +	/* the number of CMA page successful allocations */
> > +	atomic64_t nr_pages_succeeded;
> > +	/* the number of CMA page allocation failures */
> > +	atomic64_t nr_pages_failed;
> > +	struct cma_kobject *kobj;
> > +#endif
> >  };
> >  
> >  extern struct cma cma_areas[MAX_CMA_AREAS];
> > @@ -26,4 +39,11 @@ 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_pages_count(struct cma *cma, size_t count);
> > +void cma_sysfs_fail_pages_count(struct cma *cma, size_t count);
> > +#else
> > +static inline void cma_sysfs_alloc_pages_count(struct cma *cma, size_t count) {};
> > +static inline void cma_sysfs_fail_pages_count(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..ca093e9e9f64
> > --- /dev/null
> > +++ b/mm/cma_sysfs.c
> > @@ -0,0 +1,107 @@
> > +// 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"
> > +
> > +void cma_sysfs_alloc_pages_count(struct cma *cma, size_t count)
> > +{
> > +	atomic64_add(count, &cma->nr_pages_succeeded);
> > +}
> > +
> > +void cma_sysfs_fail_pages_count(struct cma *cma, size_t count)
> > +{
> > +	atomic64_add(count, &cma->nr_pages_failed);
> > +}
> > +
> > +#define CMA_ATTR_RO(_name) \
> > +	static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
> > +
> > +static ssize_t alloc_pages_success_show(struct kobject *kobj,
> > +			struct kobj_attribute *attr, char *buf)
> 
> The indentations are still wrong.
> 
> CHECK: Alignment should match open parenthesis

Hmm, I didn't know that we have that kinds of rule.
Maybe, my broken checkpatch couldn't catch it up.
Thanks.

$ ./scripts/checkpatch.pl 0001-mm-cma-support-sysfs.patch
Traceback (most recent call last):
  File "scripts/spdxcheck.py", line 6, in <module>
    from ply import lex, yacc


< snip >

> 
> > +	if (ZERO_OR_NULL_PTR(cma_kobjs))
> > +		goto out;
> > +
> > +	do {
> > +		cma = &cma_areas[i];
> > +		cma->kobj = &cma_kobjs[i];
> 
> Does cma really need are pointer to cma_kobj?

Do you mean something like this?

struct cma {
	..
	..
	struct kobject *kobj;
};

Then, how could we we make kobject dynamic model?

We need to get struct cma from kboj like below.

static ssize_t alloc_pages_success_show(struct kobject *kobj,
                                        struct kobj_attribute *attr, char *buf)
{
        struct cma_kobject *cma_kobj = container_of(kobj,
                                                    struct cma_kobject, kobj);
        struct cma *cma = cma_kobj->cma;

        return sysfs_emit(buf, "%llu\n",
                          atomic64_read(&cma->nr_pages_succeeded));
}

So kobj should be not a pointer in the container struct.
Am I missing your point? Otherwise, it would be great if you suggest
better idea.


< snip>

> > +			kobject_put(&cma->kobj->kobj);
> > +			goto out;
> > +		}
> > +	} while (++i < cma_area_count);
> > +
> > +	return 0;
> > +out:
> > +	while (--i >= 0) {
> > +		cma = &cma_areas[i];
> > +		kobject_put(&cma->kobj->kobj);
> 
> Should the cma->kobj be set to NULL by cma_kobj_release() if cma->kobj is really needed?

True. Then, let's fix cma_kobj_release, too.

> 
> > +	}
> > +
> > +	kfree(cma_kobjs);
> > +	kobject_put(cma_kobj_root);
> > +
> > +	return -ENOMEM;
> > +}
> > +subsys_initcall(cma_sysfs_init);
> > 
> 
> Tested-by: Dmitry Osipenko <digetx@gmail.com>

Thanks!

Re: [PATCH v4] mm: cma: support sysfs

[Dmitry Osipenko]

19.03.2021 21:18, Minchan Kim пишет:
>>> +	if (ZERO_OR_NULL_PTR(cma_kobjs))
>>> +		goto out;
>>> +
>>> +	do {
>>> +		cma = &cma_areas[i];
>>> +		cma->kobj = &cma_kobjs[i];
>> Does cma really need are pointer to cma_kobj?
> Do you mean something like this?
> 
> struct cma {
> 	..
> 	..
> 	struct kobject *kobj;
> };
> 
> Then, how could we we make kobject dynamic model?
> 
> We need to get struct cma from kboj like below.
> 
> static ssize_t alloc_pages_success_show(struct kobject *kobj,
>                                         struct kobj_attribute *attr, char *buf)
> {
>         struct cma_kobject *cma_kobj = container_of(kobj,
>                                                     struct cma_kobject, kobj);
>         struct cma *cma = cma_kobj->cma;
> 
>         return sysfs_emit(buf, "%llu\n",
>                           atomic64_read(&cma->nr_pages_succeeded));
> }
> 
> So kobj should be not a pointer in the container struct.
> Am I missing your point? Otherwise, it would be great if you suggest
> better idea.

I meant that cma_kobj->cma is okay, but cma->kobj wasn't really used
anywhere since struct cma can't be released. I.e. we could write
kobject_put(&cma->kobj->kobj) as kobject_put(&cma_kobjs[i].kobj);

But since we won't use the array anymore and maybe will get back to use
the cma_stat, then it will be fine to add the pointer.

Re: [PATCH v4] mm: cma: support sysfs

[Dmitry Osipenko]

19.03.2021 21:18, Minchan Kim пишет:
>>> +#define CMA_ATTR_RO(_name) \
>>> +	static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
>>> +
>>> +static ssize_t alloc_pages_success_show(struct kobject *kobj,
>>> +			struct kobj_attribute *attr, char *buf)
>> The indentations are still wrong.
>>
>> CHECK: Alignment should match open parenthesis
> Hmm, I didn't know that we have that kinds of rule.
> Maybe, my broken checkpatch couldn't catch it up.
> Thanks.
> 
> $ ./scripts/checkpatch.pl 0001-mm-cma-support-sysfs.patch
> Traceback (most recent call last):
>   File "scripts/spdxcheck.py", line 6, in <module>
>     from ply import lex, yacc
> 
> 
> < snip >
> 

That's probably because I use the --strict option of checkpatch by default.

Re: [PATCH v4] mm: cma: support sysfs

[Dmitry Osipenko]

19.03.2021 19:30, Minchan Kim пишет:
> +static void cma_kobj_release(struct kobject *kobj)
> +{
> +	struct cma_kobject *cma_kobj = container_of(kobj, struct cma_kobject, kobj);
> +
> +	kfree(cma_kobj);
> +}

Oh, wait.. I think this kfree wrong since cma_kobj belongs to the array.

Re: [PATCH v4] mm: cma: support sysfs

[Minchan Kim]

On Fri, Mar 19, 2021 at 08:56:06PM +0300, Dmitry Osipenko wrote:
> 19.03.2021 19:30, Minchan Kim пишет:
> > +static void cma_kobj_release(struct kobject *kobj)
> > +{
> > +	struct cma_kobject *cma_kobj = container_of(kobj, struct cma_kobject, kobj);
> > +
> > +	kfree(cma_kobj);
> > +}
> 
> Oh, wait.. I think this kfree wrong since cma_kobj belongs to the array.

Oh, good spot. Let me use kzalloc.

Re: [PATCH v4] mm: cma: support sysfs

[Dmitry Osipenko]

19.03.2021 21:21, Minchan Kim пишет:
> On Fri, Mar 19, 2021 at 08:56:06PM +0300, Dmitry Osipenko wrote:
>> 19.03.2021 19:30, Minchan Kim пишет:
>>> +static void cma_kobj_release(struct kobject *kobj)
>>> +{
>>> +	struct cma_kobject *cma_kobj = container_of(kobj, struct cma_kobject, kobj);
>>> +
>>> +	kfree(cma_kobj);
>>> +}
>>
>> Oh, wait.. I think this kfree wrong since cma_kobj belongs to the array.
> 
> Oh, good spot. Let me use kzalloc.
> 

Thinking a bit more about this.. it looks like actually it should be
better to get back to the older variant of cma_stat, but allocate at the
time of CMA initialization, rather than at the time of sysfs
initialization. Then the cma_stat will be decoupled from the cma struct
and cma_stat will be a self-contained object.

Re: [PATCH v4] mm: cma: support sysfs

[Minchan Kim]

On Fri, Mar 19, 2021 at 09:48:11PM +0300, Dmitry Osipenko wrote:
> 19.03.2021 21:21, Minchan Kim пишет:
> > On Fri, Mar 19, 2021 at 08:56:06PM +0300, Dmitry Osipenko wrote:
> >> 19.03.2021 19:30, Minchan Kim пишет:
> >>> +static void cma_kobj_release(struct kobject *kobj)
> >>> +{
> >>> +	struct cma_kobject *cma_kobj = container_of(kobj, struct cma_kobject, kobj);
> >>> +
> >>> +	kfree(cma_kobj);
> >>> +}
> >>
> >> Oh, wait.. I think this kfree wrong since cma_kobj belongs to the array.
> > 
> > Oh, good spot. Let me use kzalloc.
> > 
> 
> Thinking a bit more about this.. it looks like actually it should be
> better to get back to the older variant of cma_stat, but allocate at the
> time of CMA initialization, rather than at the time of sysfs
> initialization. Then the cma_stat will be decoupled from the cma struct

IIRC, the problem was slab was not initiaized at CMA init point.
That's why I liked your suggestion.

> and cma_stat will be a self-contained object.

Yeah, self-contained is better but it's already weird to
have differnt lifetime for one object since CMA object
never die, technically.

Re: [PATCH v4] mm: cma: support sysfs

[Dmitry Osipenko]

19.03.2021 22:03, Minchan Kim пишет:
> On Fri, Mar 19, 2021 at 09:48:11PM +0300, Dmitry Osipenko wrote:
>> 19.03.2021 21:21, Minchan Kim пишет:
>>> On Fri, Mar 19, 2021 at 08:56:06PM +0300, Dmitry Osipenko wrote:
>>>> 19.03.2021 19:30, Minchan Kim пишет:
>>>>> +static void cma_kobj_release(struct kobject *kobj)
>>>>> +{
>>>>> +	struct cma_kobject *cma_kobj = container_of(kobj, struct cma_kobject, kobj);
>>>>> +
>>>>> +	kfree(cma_kobj);
>>>>> +}
>>>>
>>>> Oh, wait.. I think this kfree wrong since cma_kobj belongs to the array.
>>>
>>> Oh, good spot. Let me use kzalloc.
>>>
>>
>> Thinking a bit more about this.. it looks like actually it should be
>> better to get back to the older variant of cma_stat, but allocate at the
>> time of CMA initialization, rather than at the time of sysfs
>> initialization. Then the cma_stat will be decoupled from the cma struct
> 
> IIRC, the problem was slab was not initiaized at CMA init point.
> That's why I liked your suggestion.

Alright, if CMA init time is a problem, then the recent variant should
be okay.

>> and cma_stat will be a self-contained object.
> 
> Yeah, self-contained is better but it's already weird to
> have differnt lifetime for one object since CMA object
> never die, technically.
> 

Indeed.

I found the Greg's original argument and not sure that it's really
worthwhile to worry about the copycats since this is not a driver's code..

Maybe we could just add a clarifying comment for the kobj, telling why
it's okay for CMA. Greg, doesn't it sound like a good compromise to you?

Re: [PATCH v4] mm: cma: support sysfs

[Greg Kroah-Hartman]

On Fri, Mar 19, 2021 at 10:24:03PM +0300, Dmitry Osipenko wrote:
> 19.03.2021 22:03, Minchan Kim пишет:
> > On Fri, Mar 19, 2021 at 09:48:11PM +0300, Dmitry Osipenko wrote:
> >> 19.03.2021 21:21, Minchan Kim пишет:
> >>> On Fri, Mar 19, 2021 at 08:56:06PM +0300, Dmitry Osipenko wrote:
> >>>> 19.03.2021 19:30, Minchan Kim пишет:
> >>>>> +static void cma_kobj_release(struct kobject *kobj)
> >>>>> +{
> >>>>> +	struct cma_kobject *cma_kobj = container_of(kobj, struct cma_kobject, kobj);
> >>>>> +
> >>>>> +	kfree(cma_kobj);
> >>>>> +}
> >>>>
> >>>> Oh, wait.. I think this kfree wrong since cma_kobj belongs to the array.
> >>>
> >>> Oh, good spot. Let me use kzalloc.
> >>>
> >>
> >> Thinking a bit more about this.. it looks like actually it should be
> >> better to get back to the older variant of cma_stat, but allocate at the
> >> time of CMA initialization, rather than at the time of sysfs
> >> initialization. Then the cma_stat will be decoupled from the cma struct
> > 
> > IIRC, the problem was slab was not initiaized at CMA init point.
> > That's why I liked your suggestion.
> 
> Alright, if CMA init time is a problem, then the recent variant should
> be okay.
> 
> >> and cma_stat will be a self-contained object.
> > 
> > Yeah, self-contained is better but it's already weird to
> > have differnt lifetime for one object since CMA object
> > never die, technically.
> > 
> 
> Indeed.
> 
> I found the Greg's original argument and not sure that it's really
> worthwhile to worry about the copycats since this is not a driver's code..
> 
> Maybe we could just add a clarifying comment for the kobj, telling why
> it's okay for CMA. Greg, doesn't it sound like a good compromise to you?

Please no.

Re: [PATCH v4] mm: cma: support sysfs

[Dmitry Osipenko]

20.03.2021 10:52, Greg Kroah-Hartman пишет:
..
>> I found the Greg's original argument and not sure that it's really
>> worthwhile to worry about the copycats since this is not a driver's code..
>>
>> Maybe we could just add a clarifying comment for the kobj, telling why
>> it's okay for CMA. Greg, doesn't it sound like a good compromise to you?
> 
> Please no.
> 

In the case of a static objects, like CMA, this creates more bad than
good, IMO. Even experienced developers are getting confused. In the end
it's up to you guys to decide what to choose, either way will work.

Re: [PATCH v4] mm: cma: support sysfs

[Dmitry Osipenko]

19.03.2021 16:39, Dmitry Osipenko пишет:
> 19.03.2021 15:44, Dmitry Osipenko пишет:
> ...
>>>  #include <linux/debugfs.h>
>>> +#include <linux/kobject.h>
>>> +
>>> +struct cma_stat {
>>> +	spinlock_t lock;
>>> +	/* the number of CMA page successful allocations */
>>> +	unsigned long nr_pages_succeeded;
>>> +	/* the number of CMA page allocation failures */
>>> +	unsigned long nr_pages_failed;
>>> +	struct kobject kobj;
>>> +};
>>>  
>>>  struct cma {
>>>  	unsigned long   base_pfn;
>>> @@ -16,6 +26,9 @@ struct cma {
>>>  	struct debugfs_u32_array dfs_bitmap;
>>>  #endif
>>>  	char name[CMA_MAX_NAME];
>>> +#ifdef CONFIG_CMA_SYSFS
>>> +	struct cma_stat	*stat;
>>> +#endif
> 
> What is the point of allocating stat dynamically?
> 
> ...
>>> +void cma_sysfs_alloc_pages_count(struct cma *cma, size_t count)
>>> +{
>>> +	spin_lock(&cma->stat->lock);
>>> +	cma->stat->nr_pages_succeeded += count;
>>> +	spin_unlock(&cma->stat->lock);
>>> +}
>>> +
>>> +void cma_sysfs_fail_pages_count(struct cma *cma, size_t count)
>>> +{
>>> +	spin_lock(&cma->stat->lock);
>>> +	cma->stat->nr_pages_failed += count;
>>> +	spin_unlock(&cma->stat->lock);
>>> +}
> 
> You could use atomic increment and then locking isn't needed.
> 

Actually, the counter should be u64 in order not to worry about overflow.

[PATCH v4] mm: cma: support sysfs

[Minchan Kim]

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 statistics for CMA, in order to provide
some basic monitoring of the CMA allocator.

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

These two values allow the user to calcuate the allocation
failure rate for each CMA area.

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

The cma_stat was intentionally allocated by dynamic allocation
to harmonize with kobject lifetime management.
https://lore.kernel.org/linux-mm/YCOAmXqt6dZkCQYs@kroah.com/

Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
From v3 - https://lore.kernel.org/linux-mm/20210303205053.2906924-1-minchan@kernel.org/
 * kmalloc_array - akpm
 * add why cma_stat was implemented by dynamic allocation - akpm
 * use !__GFP_NOWARN facility to print error - akpm

From v2 - https://lore.kernel.org/linux-mm/20210208180142.2765456-1-minchan@kernel.org/
 * sysfs doc and description modification - jhubbard

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                                | 110 ++++++++++++++++++
 6 files changed, 166 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..f518af819cee
--- /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 subdirectory for each CMA
+		heap name (also sometimes called CMA areas).
+
+		Each CMA heap subdirectory (that is, each
+		/sys/kernel/mm/cma/<cma-heap-name> directory) contains the
+		following items:
+
+			cma_alloc_pages_attempts
+			cma_alloc_pages_fails
+
+What:		/sys/kernel/mm/cma/<cma-heap-name>/cma_alloc_pages_attempts
+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_fails
+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 24c045b24b95..febb7e8e24de 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 72227b24a616..56968b23ed7a 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 54eee2119822..551b704faeaf 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__, cma->name, count, ret);
 		cma_debug_show_areas(cma);
 	}
+out:
+	if (!page)
+		cma_sysfs_fail_count(cma, count);
 
 	pr_debug("%s(): returned %p\n", __func__, page);
 	return page;
diff --git a/mm/cma.h b/mm/cma.h
index 42ae082cb067..24a1d61eabc7 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_attempts;	/* the number of CMA page allocation attempts */
+	unsigned long pages_fails;	/* 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_count(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_count(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..67b63167eaf5
--- /dev/null
+++ b/mm/cma_sysfs.c
@@ -0,0 +1,110 @@
+// 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_attempts += count;
+	spin_unlock(&cma->stat->lock);
+}
+
+void cma_sysfs_fail_count(struct cma *cma, size_t count)
+{
+	spin_lock(&cma->stat->lock);
+	cma->stat->pages_fails += 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_attempts_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_attempts);
+}
+CMA_ATTR_RO(cma_alloc_pages_attempts);
+
+static ssize_t cma_alloc_pages_fails_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_fails);
+}
+CMA_ATTR_RO(cma_alloc_pages_fails);
+
+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_attempts_attr.attr,
+	&cma_alloc_pages_fails_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)
+		return -ENOMEM;
+
+	cma_stats = kmalloc_array(cma_area_count, sizeof(struct cma_stat),
+				GFP_KERNEL|__GFP_ZERO);
+	if (!cma_stats)
+		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);
-- 
2.30.1.766.gb4fecdf3b7-goog

Re: [PATCH v4] mm: cma: support sysfs

[David Hildenbrand]

On 04.03.21 17:17, Minchan Kim wrote:
> 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 statistics for CMA, in order to provide
> some basic monitoring of the CMA allocator.
> 
>   * the number of CMA page allocation attempts
>   * the number of CMA page allocation failures
> 
> These two values allow the user to calcuate the allocation
> failure rate for each CMA area.
> 
> e.g.)
>    /sys/kernel/mm/cma/WIFI/cma_alloc_pages_[attempts|fails]
>    /sys/kernel/mm/cma/SENSOR/cma_alloc_pages_[attempts|fails]
>    /sys/kernel/mm/cma/BLUETOOTH/cma_alloc_pages_[attempts|fails]
> 
> The cma_stat was intentionally allocated by dynamic allocation
> to harmonize with kobject lifetime management.
> https://lore.kernel.org/linux-mm/YCOAmXqt6dZkCQYs@kroah.com/
> 
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Reviewed-by: John Hubbard <jhubbard@nvidia.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>  From v3 - https://lore.kernel.org/linux-mm/20210303205053.2906924-1-minchan@kernel.org/
>   * kmalloc_array - akpm
>   * add why cma_stat was implemented by dynamic allocation - akpm
>   * use !__GFP_NOWARN facility to print error - akpm
> 
>  From v2 - https://lore.kernel.org/linux-mm/20210208180142.2765456-1-minchan@kernel.org/
>   * sysfs doc and description modification - jhubbard
> 
>  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                                | 110 ++++++++++++++++++
>   6 files changed, 166 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..f518af819cee
> --- /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 subdirectory for each CMA
> +		heap name (also sometimes called CMA areas).
> +
> +		Each CMA heap subdirectory (that is, each
> +		/sys/kernel/mm/cma/<cma-heap-name> directory) contains the
> +		following items:
> +
> +			cma_alloc_pages_attempts
> +			cma_alloc_pages_fails

Nit: why "cma_" again when we are already under "/cma/" ?

I'd simply go with something like

"total_alloc_attempts"
"failed_alloc_attempts"

But maybe this has been discussed already.

> +
> +What:		/sys/kernel/mm/cma/<cma-heap-name>/cma_alloc_pages_attempts
> +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_fails
> +Date:		Feb 2021
> +Contact:	Minchan Kim <minchan@kernel.org>
> +Description:
> +		the number of pages CMA API failed to allocate

This will be useful.

-- 
Thanks,

David / dhildenb

Re: [PATCH v4] mm: cma: support sysfs

[Minchan Kim]

On Fri, Mar 05, 2021 at 06:34:22PM +0100, David Hildenbrand wrote:
> On 04.03.21 17:17, Minchan Kim wrote:
> > 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 statistics for CMA, in order to provide
> > some basic monitoring of the CMA allocator.
> > 
> >   * the number of CMA page allocation attempts
> >   * the number of CMA page allocation failures
> > 
> > These two values allow the user to calcuate the allocation
> > failure rate for each CMA area.
> > 
> > e.g.)
> >    /sys/kernel/mm/cma/WIFI/cma_alloc_pages_[attempts|fails]
> >    /sys/kernel/mm/cma/SENSOR/cma_alloc_pages_[attempts|fails]
> >    /sys/kernel/mm/cma/BLUETOOTH/cma_alloc_pages_[attempts|fails]
> > 
> > The cma_stat was intentionally allocated by dynamic allocation
> > to harmonize with kobject lifetime management.
> > https://lore.kernel.org/linux-mm/YCOAmXqt6dZkCQYs@kroah.com/
> > 
> > Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Reviewed-by: John Hubbard <jhubbard@nvidia.com>
> > Signed-off-by: Minchan Kim <minchan@kernel.org>
> > ---
> >  From v3 - https://lore.kernel.org/linux-mm/20210303205053.2906924-1-minchan@kernel.org/
> >   * kmalloc_array - akpm
> >   * add why cma_stat was implemented by dynamic allocation - akpm
> >   * use !__GFP_NOWARN facility to print error - akpm
> > 
> >  From v2 - https://lore.kernel.org/linux-mm/20210208180142.2765456-1-minchan@kernel.org/
> >   * sysfs doc and description modification - jhubbard
> > 
> >  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                                | 110 ++++++++++++++++++
> >   6 files changed, 166 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..f518af819cee
> > --- /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 subdirectory for each CMA
> > +		heap name (also sometimes called CMA areas).
> > +
> > +		Each CMA heap subdirectory (that is, each
> > +		/sys/kernel/mm/cma/<cma-heap-name> directory) contains the
> > +		following items:
> > +
> > +			cma_alloc_pages_attempts
> > +			cma_alloc_pages_fails
> 
> Nit: why "cma_" again when we are already under "/cma/" ?

Originally, there was desire to add cma_alloc_attempts as well as
cma_alloc_pages_attempts. 

> 
> I'd simply go with something like
> 
> "total_alloc_attempts"
> "failed_alloc_attempts"

If we really want to remove the cma prefix, maybe,

alloc_pages_attempts
alloc_pages_fails

If someone want to count cma_alloc itself, Then

alloc_success
alloc_fail

Does that make sense?