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

Minchan Kim
2021-02-08T23:37:43Z

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