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Message-ID: <CAPTztWbF+VLO6g=7VKk-tYHdtZ781Hbj5ucW6i8Gf9TJiiebWg@mail.gmail.com>
Date: Mon, 22 Jul 2024 09:24:58 -0700
From: Frank van der Linden <fvdl@...gle.com>
To: linux-mm@...ck.org, akpm@...ux-foundation.org
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/cma: export total and free number of pages for CMA areas
On Tue, Jul 9, 2024 at 9:31 AM Frank van der Linden <fvdl@...gle.com> wrote:
>
> In addition to the number of allocations and releases, system
> management software may like to be aware of the size of CMA
> areas, and how many pages are available in it. This information
> is currently not available, so export it in total_page and
> available_pages, respectively.
>
> The name 'available_pages' was picked over 'free_pages' because
> 'free' implies that the pages are unused. But they might not
> be, they just haven't been used by cma_alloc
>
> The number of available pages is tracked regardless of
> CONFIG_CMA_SYSFS, allowing for a few minor shortcuts in
> the code, avoiding bitmap operations.
>
> Signed-off-by: Frank van der Linden <fvdl@...gle.com>
> ---
> Documentation/ABI/testing/sysfs-kernel-mm-cma | 13 ++++++++++++
> mm/cma.c | 18 +++++++++++------
> mm/cma.h | 1 +
> mm/cma_debug.c | 5 +----
> mm/cma_sysfs.c | 20 +++++++++++++++++++
> 5 files changed, 47 insertions(+), 10 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-kernel-mm-cma b/Documentation/ABI/testing/sysfs-kernel-mm-cma
> index dfd755201142..aaf2a5d8b13b 100644
> --- a/Documentation/ABI/testing/sysfs-kernel-mm-cma
> +++ b/Documentation/ABI/testing/sysfs-kernel-mm-cma
> @@ -29,3 +29,16 @@ Date: Feb 2024
> Contact: Anshuman Khandual <anshuman.khandual@....com>
> Description:
> the number of pages CMA API succeeded to release
> +
> +What: /sys/kernel/mm/cma/<cma-heap-name>/total_pages
> +Date: Jun 2024
> +Contact: Frank van der Linden <fvdl@...gle.com>
> +Description:
> + The size of the CMA area in pages.
> +
> +What: /sys/kernel/mm/cma/<cma-heap-name>/available_pages
> +Date: Jun 2024
> +Contact: Frank van der Linden <fvdl@...gle.com>
> +Description:
> + The number of pages in the CMA area that are still
> + available for CMA allocation.
> diff --git a/mm/cma.c b/mm/cma.c
> index 3e9724716bad..727e8c04d53a 100644
> --- a/mm/cma.c
> +++ b/mm/cma.c
> @@ -86,6 +86,7 @@ static void cma_clear_bitmap(struct cma *cma, unsigned long pfn,
>
> spin_lock_irqsave(&cma->lock, flags);
> bitmap_clear(cma->bitmap, bitmap_no, bitmap_count);
> + cma->available_count += count;
> spin_unlock_irqrestore(&cma->lock, flags);
> }
>
> @@ -133,7 +134,7 @@ static void __init cma_activate_area(struct cma *cma)
> free_reserved_page(pfn_to_page(pfn));
> }
> totalcma_pages -= cma->count;
> - cma->count = 0;
> + cma->available_count = cma->count = 0;
> pr_err("CMA area %s could not be activated\n", cma->name);
> return;
> }
> @@ -198,7 +199,7 @@ int __init cma_init_reserved_mem(phys_addr_t base, phys_addr_t size,
> snprintf(cma->name, CMA_MAX_NAME, "cma%d\n", cma_area_count);
>
> cma->base_pfn = PFN_DOWN(base);
> - cma->count = size >> PAGE_SHIFT;
> + cma->available_count = cma->count = size >> PAGE_SHIFT;
> cma->order_per_bit = order_per_bit;
> *res_cma = cma;
> cma_area_count++;
> @@ -382,7 +383,7 @@ static void cma_debug_show_areas(struct cma *cma)
> {
> unsigned long next_zero_bit, next_set_bit, nr_zero;
> unsigned long start = 0;
> - unsigned long nr_part, nr_total = 0;
> + unsigned long nr_part;
> unsigned long nbits = cma_bitmap_maxno(cma);
>
> spin_lock_irq(&cma->lock);
> @@ -394,12 +395,12 @@ static void cma_debug_show_areas(struct cma *cma)
> next_set_bit = find_next_bit(cma->bitmap, nbits, next_zero_bit);
> nr_zero = next_set_bit - next_zero_bit;
> nr_part = nr_zero << cma->order_per_bit;
> - pr_cont("%s%lu@%lu", nr_total ? "+" : "", nr_part,
> + pr_cont("%s%lu@%lu", start ? "+" : "", nr_part,
> next_zero_bit);
> - nr_total += nr_part;
> start = next_zero_bit + nr_zero;
> }
> - pr_cont("=> %lu free of %lu total pages\n", nr_total, cma->count);
> + pr_cont("=> %lu free of %lu total pages\n", cma->available_count,
> + cma->count);
> spin_unlock_irq(&cma->lock);
> }
>
> @@ -446,6 +447,10 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
>
> for (;;) {
> spin_lock_irq(&cma->lock);
> + if (count > cma->available_count) {
> + spin_unlock_irq(&cma->lock);
> + break;
> + }
> bitmap_no = bitmap_find_next_zero_area_off(cma->bitmap,
> bitmap_maxno, start, bitmap_count, mask,
> offset);
> @@ -454,6 +459,7 @@ struct page *cma_alloc(struct cma *cma, unsigned long count,
> break;
> }
> bitmap_set(cma->bitmap, bitmap_no, bitmap_count);
> + cma->available_count -= count;
> /*
> * It's safe to drop the lock here. We've marked this region for
> * our exclusive use. If the migration fails we will take the
> diff --git a/mm/cma.h b/mm/cma.h
> index ad61cc6dd439..d111f3d51868 100644
> --- a/mm/cma.h
> +++ b/mm/cma.h
> @@ -13,6 +13,7 @@ struct cma_kobject {
> struct cma {
> unsigned long base_pfn;
> unsigned long count;
> + unsigned long available_count;
> unsigned long *bitmap;
> unsigned int order_per_bit; /* Order of pages represented by one bit */
> spinlock_t lock;
> diff --git a/mm/cma_debug.c b/mm/cma_debug.c
> index 602fff89b15f..89236f22230a 100644
> --- a/mm/cma_debug.c
> +++ b/mm/cma_debug.c
> @@ -34,13 +34,10 @@ DEFINE_DEBUGFS_ATTRIBUTE(cma_debugfs_fops, cma_debugfs_get, NULL, "%llu\n");
> static int cma_used_get(void *data, u64 *val)
> {
> struct cma *cma = data;
> - unsigned long used;
>
> spin_lock_irq(&cma->lock);
> - /* pages counter is smaller than sizeof(int) */
> - used = bitmap_weight(cma->bitmap, (int)cma_bitmap_maxno(cma));
> + *val = cma->count - cma->available_count;
> spin_unlock_irq(&cma->lock);
> - *val = (u64)used << cma->order_per_bit;
>
> return 0;
> }
> diff --git a/mm/cma_sysfs.c b/mm/cma_sysfs.c
> index f50db3973171..97acd3e5a6a5 100644
> --- a/mm/cma_sysfs.c
> +++ b/mm/cma_sysfs.c
> @@ -62,6 +62,24 @@ static ssize_t release_pages_success_show(struct kobject *kobj,
> }
> CMA_ATTR_RO(release_pages_success);
>
> +static ssize_t total_pages_show(struct kobject *kobj,
> + struct kobj_attribute *attr, char *buf)
> +{
> + struct cma *cma = cma_from_kobj(kobj);
> +
> + return sysfs_emit(buf, "%lu\n", cma->count);
> +}
> +CMA_ATTR_RO(total_pages);
> +
> +static ssize_t available_pages_show(struct kobject *kobj,
> + struct kobj_attribute *attr, char *buf)
> +{
> + struct cma *cma = cma_from_kobj(kobj);
> +
> + return sysfs_emit(buf, "%lu\n", cma->available_count);
> +}
> +CMA_ATTR_RO(available_pages);
> +
> static void cma_kobj_release(struct kobject *kobj)
> {
> struct cma *cma = cma_from_kobj(kobj);
> @@ -75,6 +93,8 @@ static struct attribute *cma_attrs[] = {
> &alloc_pages_success_attr.attr,
> &alloc_pages_fail_attr.attr,
> &release_pages_success_attr.attr,
> + &total_pages_attr.attr,
> + &available_pages_attr.attr,
> NULL,
> };
> ATTRIBUTE_GROUPS(cma);
> --
> 2.45.2.803.g4e1b14247a-goog
>
I realize that this isn't the most exciting patch, but.. any comments? :)
- Frank
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