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

Dmitry Osipenko
2021-03-19T12:44:57Z

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)