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

[Minchan Kim <minchan@kernel.org>]

On Mon, Feb 08, 2021 at 01:34:06PM -0800, John Hubbard wrote:
> 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.

Yub, take it.

> 
> > 
> >   * 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.

Good to me.

> 
> > 
> > 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
> 

Yub.

> 
> > +
> > +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.

Sure.

> 
> > +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.

Oops.

> 
> >   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.

Originally, I went with the object lifetime with struct cma as you
suggested to make code simple. However, Greg KH wanted to have
release for kobj_type since it is consistent with other kboject
handling.


> 
> 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