Re: [PATCH v2] mm: cma: support sysfs

John Hubbard
2021-02-08T21:49:28Z

On 2/8/21 10:01 AM, 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 for the CMA and exposes stats below
> to keep monitor for telemetric in the system.

Or:

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

Maybe:

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_[attempt|fail]
> /sys/kernel/mm/cma/SENSOR/cma_alloc_pages_[attempt|fail]
> /sys/kernel/mm/cma/BLUETOOTH/cma_alloc_pages_[attempt|fail]
>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---
>
> From v1 - https://lore.kernel.org/linux-mm/20210203155001.4121868-1-minchan@kernel.org/
> * fix sysfs build and refactoring - willy
> * rename and drop some attributes - jhubbard
>
> Documentation/ABI/testing/sysfs-kernel-mm-cma | 25 ++++
> mm/Kconfig | 7 ++
> mm/Makefile | 1 +
> mm/cma.c | 6 +-
> mm/cma.h | 18 +++
> mm/cma_sysfs.c | 114 ++++++++++++++++++
> 6 files changed, 170 insertions(+), 1 deletion(-)
> create mode 100644 Documentation/ABI/testing/sysfs-kernel-mm-cma
> create mode 100644 mm/cma_sysfs.c
>
> diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-cma b/Documentation/ABI/testing/sysfs-kernel-mm-cma
> new file mode 100644
> index 000000000000..68bdcc8c7681
> --- /dev/null
> +++ b/Documentation/ABI/testing/sysfs-kernel-mm-cma
> @@ -0,0 +1,25 @@
> +What: /sys/kernel/mm/cma/
> +Date: Feb 2021
> +Contact: Minchan Kim <minchan@kernel.org>
> +Description:
> + /sys/kernel/mm/cma/ contains a number of subdirectories by
> + cma-heap name. The subdirectory contains a number of files
> + to represent cma allocation statistics.
> +
> + There are number of files under
> + /sys/kernel/mm/cma/<cma-heap-name> directory
> +
> + - cma_alloc_pages_attempt
> + - cma_alloc_pages_fail

How about this instead:
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_attempt
cma_alloc_pages_fail

> +
> +What: /sys/kernel/mm/cma/<cma-heap-name>/cma_alloc_pages_attempt

Actually, shall we change that from "attempt" to "attempts"? Otherwise, the
language is a little odd there.

> +Date: Feb 2021
> +Contact: Minchan Kim <minchan@kernel.org>
> +Description:
> + the number of pages CMA API tried to allocate
> +
> +What: /sys/kernel/mm/cma/<cma-heap-name>/cma_alloc_pages_fail
> +Date: Feb 2021
> +Contact: Minchan Kim <minchan@kernel.org>
> +Description:
> + the number of pages CMA API failed to allocate
> diff --git a/mm/Kconfig b/mm/Kconfig
> index ec35bf406439..ad7e9c065657 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -513,6 +513,13 @@ config CMA_DEBUGFS
> help
> Turns on the DebugFS interface for CMA.
>
> +config CMA_SYSFS
> + bool "CMA information through sysfs interface"
> + depends on CMA && SYSFS
> + help
> + This option exposes some sysfs attributes to get information
> + from CMA.
> +
> config CMA_AREAS
> int "Maximum count of the CMA areas"
> depends on CMA
> diff --git a/mm/Makefile b/mm/Makefile
> index b2a564eec27f..0ae764e5b1a8 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -109,6 +109,7 @@ obj-$(CONFIG_CMA) += cma.o
> obj-$(CONFIG_MEMORY_BALLOON) += balloon_compaction.o
> obj-$(CONFIG_PAGE_EXTENSION) += page_ext.o
> obj-$(CONFIG_CMA_DEBUGFS) += cma_debug.o
> +obj-$(CONFIG_CMA_SYSFS) += cma_sysfs.o

Remove the unnecessary tab there, none of the other nearby lines have one.

> obj-$(CONFIG_USERFAULTFD) += userfaultfd.o
> obj-$(CONFIG_IDLE_PAGE_TRACKING) += page_idle.o
> obj-$(CONFIG_DEBUG_PAGE_REF) += debug_page_ref.o
> diff --git a/mm/cma.c b/mm/cma.c
> index 23d4a97c834a..0611202d6e7d 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -447,9 +447,10 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
> offset = cma_bitmap_aligned_offset(cma, align);
> bitmap_maxno = cma_bitmap_maxno(cma);
> bitmap_count = cma_bitmap_pages_to_bits(cma, count);
> + cma_sysfs_alloc_count(cma, count);
>
> if (bitmap_count > bitmap_maxno)
> - return NULL;
> + goto out;
>
> for (;;) {
> mutex_lock(&cma->lock);
> @@ -504,6 +505,9 @@ struct page *cma_alloc(struct cma *cma, size_t count, unsigned int align,
> __func__, count, ret);
> cma_debug_show_areas(cma);
> }
> +out:
> + if (!page)
> + cma_sysfs_fail(cma, count);
>
> pr_debug("%s(): returned %p\n", __func__, page);
> return page;
> diff --git a/mm/cma.h b/mm/cma.h
> index 42ae082cb067..49a8ceddd9e8 100644
> --- a/mm/cma.h
> +++ b/mm/cma.h
> @@ -3,6 +3,14 @@
> #define __MM_CMA_H__
>
> #include <linux/debugfs.h>
> +#include <linux/kobject.h>
> +
> +struct cma_stat {
> + spinlock_t lock;
> + unsigned long pages_attempt; /* the number of CMA page allocation attempts */
> + unsigned long pages_fail; /* the number of CMA page allocation failures */
> + struct kobject kobj;
> +};
>
> struct cma {
> unsigned long base_pfn;
> @@ -16,6 +24,9 @@ struct cma {
> struct debugfs_u32_array dfs_bitmap;
> #endif
> char name[CMA_MAX_NAME];
> +#ifdef CONFIG_CMA_SYSFS
> + struct cma_stat *stat;

This should not be a pointer. By making it a pointer, you've added a bunch of pointless
extra code to the implementation.

Here's a diff to implement the non-pointer way, and also to fix a build error in this
patch (missing semicolon):

diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-cma
b/Documentation/ABI/testing/sysfs-kernel-mm-cma
index 68bdcc8c7681..f3769b4e1a3c 100644
--- a/Documentation/ABI/testing/sysfs-kernel-mm-cma
+++ b/Documentation/ABI/testing/sysfs-kernel-mm-cma
@@ -2,15 +2,15 @@ What: /sys/kernel/mm/cma/
Date: Feb 2021
Contact: Minchan Kim <minchan@kernel.org>
Description:
- /sys/kernel/mm/cma/ contains a number of subdirectories by
- cma-heap name. The subdirectory contains a number of files
- to represent cma allocation statistics.
+ /sys/kernel/mm/cma/ contains a subdirectory for each CMA heap name (also
+ sometimes called CMA areas).

- There are number of files under
- /sys/kernel/mm/cma/<cma-heap-name> directory
+ Each CMA heap subdirectory (that is, each
+ /sys/kernel/mm/cma/<cma-heap-name> directory) contains the following
+ items:

- - cma_alloc_pages_attempt
- - cma_alloc_pages_fail
+ cma_alloc_pages_attempt
+ cma_alloc_pages_fail

What: /sys/kernel/mm/cma/<cma-heap-name>/cma_alloc_pages_attempt
Date: Feb 2021
diff --git a/mm/cma.h b/mm/cma.h
index 49a8ceddd9e8..1e109830f553 100644
--- a/mm/cma.h
+++ b/mm/cma.h
@@ -25,7 +25,7 @@ struct cma {
#endif
char name[CMA_MAX_NAME];
#ifdef CONFIG_CMA_SYSFS
- struct cma_stat *stat;
+ struct cma_stat stat;
#endif
};

diff --git a/mm/cma_sysfs.c b/mm/cma_sysfs.c
index 1f6b9f785825..52905694b6b7 100644
--- a/mm/cma_sysfs.c
+++ b/mm/cma_sysfs.c
@@ -11,20 +11,18 @@

#include "cma.h"

-static struct cma_stat *cma_stats;
-
void cma_sysfs_alloc_count(struct cma *cma, size_t count)
{
- spin_lock(&cma->stat->lock);
- cma->stat->pages_attempt += count;
- spin_unlock(&cma->stat->lock);
+ spin_lock(&cma->stat.lock);
+ cma->stat.pages_attempt += count;
+ spin_unlock(&cma->stat.lock);
}

void cma_sysfs_fail(struct cma *cma, size_t count)
{
- spin_lock(&cma->stat->lock);
- cma->stat->pages_fail += count;
- spin_unlock(&cma->stat->lock);
+ spin_lock(&cma->stat.lock);
+ cma->stat.pages_fail += count;
+ spin_unlock(&cma->stat.lock);
}

#define CMA_ATTR_RO(_name) \
@@ -50,13 +48,6 @@ static ssize_t cma_alloc_pages_fail_show(struct kobject *kobj,
}
CMA_ATTR_RO(cma_alloc_pages_fail);

-static void cma_kobj_release(struct kobject *kobj)
-{
- struct cma_stat *stat = container_of(kobj, struct cma_stat, kobj);
-
- kfree(stat);
-}
-
static struct attribute *cma_attrs[] = {
&cma_alloc_pages_attempt_attr.attr,
&cma_alloc_pages_fail_attr.attr,
@@ -65,7 +56,6 @@ static struct attribute *cma_attrs[] = {
ATTRIBUTE_GROUPS(cma);

static struct kobj_type cma_ktype = {
- .release = cma_kobj_release,
.sysfs_ops = &kobj_sysfs_ops,
.default_groups = cma_groups
};
@@ -81,32 +71,23 @@ static int __init cma_sysfs_init(void)
return -ENOMEM;
}

- cma_stats = kzalloc(array_size(sizeof(struct cma_stat),
- cma_area_count), GFP_KERNEL);
- if (!cma_stats) {
- pr_err("failed to create cma_stats\n");
- goto out;
- }
-
do {
cma = &cma_areas[i];
- cma->stat = &cma_stats[i];
- spin_lock_init(&cma->stat->lock);
- if (kobject_init_and_add(&cma->stat->kobj, &cma_ktype,
+ 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);
+ kobject_put(&cma->stat.kobj);
goto out;
}
- } while (++i < cma_area_count)
+ } while (++i < cma_area_count);

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

- kfree(cma_stats);
kobject_put(cma_kobj);

return -ENOMEM;

> +#endif
> };
>
> extern struct cma cma_areas[MAX_CMA_AREAS];
> @@ -26,4 +37,11 @@ static inline unsigned long cma_bitmap_maxno(struct cma *cma)
> return cma->count >> cma->order_per_bit;
> }
>
> +#ifdef CONFIG_CMA_SYSFS
> +void cma_sysfs_alloc_count(struct cma *cma, size_t count);
> +void cma_sysfs_fail(struct cma *cma, size_t count);
> +#else
> +static inline void cma_sysfs_alloc_count(struct cma *cma, size_t count) {};
> +static inline void cma_sysfs_fail(struct cma *cma, size_t count) {};
> +#endif
> #endif
> diff --git a/mm/cma_sysfs.c b/mm/cma_sysfs.c
> new file mode 100644
> index 000000000000..1f6b9f785825
> --- /dev/null
> +++ b/mm/cma_sysfs.c
> @@ -0,0 +1,114 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * CMA SysFS Interface
> + *
> + * Copyright (c) 2021 Minchan Kim <minchan@kernel.org>
> + */
> +
> +#include <linux/cma.h>
> +#include <linux/kernel.h>
> +#include <linux/slab.h>
> +
> +#include "cma.h"
> +
> +static struct cma_stat *cma_stats;

I don't know what that's for but it definitely is not needed if you make cma.stat
not a pointer, and not in any other case either.

> +
> +void cma_sysfs_alloc_count(struct cma *cma, size_t count)
> +{
> + spin_lock(&cma->stat->lock);
> + cma->stat->pages_attempt += count;
> + spin_unlock(&cma->stat->lock);
> +}
> +
> +void cma_sysfs_fail(struct cma *cma, size_t count)
> +{
> + spin_lock(&cma->stat->lock);
> + cma->stat->pages_fail += count;
> + spin_unlock(&cma->stat->lock);
> +}
> +
> +#define CMA_ATTR_RO(_name) \
> + static struct kobj_attribute _name##_attr = __ATTR_RO(_name)
> +
> +static struct kobject *cma_kobj;
> +
> +static ssize_t cma_alloc_pages_attempt_show(struct kobject *kobj,
> + struct kobj_attribute *attr, char *buf)
> +{
> + struct cma_stat *stat = container_of(kobj, struct cma_stat, kobj);
> +
> + return sysfs_emit(buf, "%lu\n", stat->pages_attempt);
> +}
> +CMA_ATTR_RO(cma_alloc_pages_attempt);
> +
> +static ssize_t cma_alloc_pages_fail_show(struct kobject *kobj,
> + struct kobj_attribute *attr, char *buf)
> +{
> + struct cma_stat *stat = container_of(kobj, struct cma_stat, kobj);
> +
> + return sysfs_emit(buf, "%lu\n", stat->pages_fail);
> +}
> +CMA_ATTR_RO(cma_alloc_pages_fail);
> +
> +static void cma_kobj_release(struct kobject *kobj)
> +{
> + struct cma_stat *stat = container_of(kobj, struct cma_stat, kobj);
> +
> + kfree(stat);
> +}
> +
> +static struct attribute *cma_attrs[] = {
> + &cma_alloc_pages_attempt_attr.attr,
> + &cma_alloc_pages_fail_attr.attr,
> + NULL,
> +};
> +ATTRIBUTE_GROUPS(cma);
> +
> +static struct kobj_type cma_ktype = {
> + .release = cma_kobj_release,
> + .sysfs_ops = &kobj_sysfs_ops,
> + .default_groups = cma_groups
> +};
> +
> +static int __init cma_sysfs_init(void)
> +{
> + int i = 0;
> + struct cma *cma;
> +
> + cma_kobj = kobject_create_and_add("cma", mm_kobj);
> + if (!cma_kobj) {
> + pr_err("failed to create cma kobject\n");
> + return -ENOMEM;
> + }
> +
> + cma_stats = kzalloc(array_size(sizeof(struct cma_stat),
> + cma_area_count), GFP_KERNEL);
> + if (!cma_stats) {
> + pr_err("failed to create cma_stats\n");
> + goto out;
> + }
> +
> + do {
> + cma = &cma_areas[i];
> + cma->stat = &cma_stats[i];
> + spin_lock_init(&cma->stat->lock);
> + if (kobject_init_and_add(&cma->stat->kobj, &cma_ktype,
> + cma_kobj, "%s", cma->name)) {
> + kobject_put(&cma->stat->kobj);
> + goto out;
> + }
> + } while (++i < cma_area_count)

This clearly is not going to compile! Don't forget to build and test the
patches.

> +
> + 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);
>

thanks,
--
John Hubbard
NVIDIA