Re: [PATCH v2] mm/page_alloc: count CMA pages per zone and print them in /proc/zoneinfo

Oscar Salvador
2021-01-28T21:44:17Z

On Thu, Jan 28, 2021 at 05:45:33PM +0100, David Hildenbrand wrote:
> Let's count the number of CMA pages per zone and print them in
> /proc/zoneinfo.
>
> Having access to the total number of CMA pages per zone is helpful for
> debugging purposes to know where exactly the CMA pages ended up, and to
> figure out how many pages of a zone might behave differently, even after
> some of these pages might already have been allocated.
>
> As one example, CMA pages part of a kernel zone cannot be used for
> ordinary kernel allocations but instead behave more like ZONE_MOVABLE.
>
> For now, we are only able to get the global nr+free cma pages from
> /proc/meminfo and the free cma pages per zone from /proc/zoneinfo.
>
> Example after this patch when booting a 6 GiB QEMU VM with
> "hugetlb_cma=2G":
> # cat /proc/zoneinfo | grep cma
> cma 0
> nr_free_cma 0
> cma 0
> nr_free_cma 0
> cma 524288
> nr_free_cma 493016
> cma 0
> cma 0
> # cat /proc/meminfo | grep Cma
> CmaTotal: 2097152 kB
> CmaFree: 1972064 kB
>
> Note: We track/print only with CONFIG_CMA; "nr_free_cma" in /proc/zoneinfo
> is currently also printed without CONFIG_CMA.
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
> Cc: Mike Rapoport <rppt@kernel.org>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Michal Hocko <mhocko@kernel.org>
> Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
> Cc: linux-api@vger.kernel.org
> Signed-off-by: David Hildenbrand <david@redhat.com>

IMHO looks better to me, thanks:

Reviewed-by: Oscar Salvador <osalvador@suse.de>

> ---
>
> v1 -> v2:
> - Print/track only with CONFIG_CMA
> - Extend patch description
>
> ---
> include/linux/mmzone.h | 6 ++++++
> mm/page_alloc.c | 1 +
> mm/vmstat.c | 5 +++++
> 3 files changed, 12 insertions(+)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index ae588b2f87ef..27d22fb22e05 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -503,6 +503,9 @@ struct zone {
> * bootmem allocator):
> * managed_pages = present_pages - reserved_pages;
> *
> + * cma pages is present pages that are assigned for CMA use
> + * (MIGRATE_CMA).
> + *
> * So present_pages may be used by memory hotplug or memory power
> * management logic to figure out unmanaged pages by checking
> * (present_pages - managed_pages). And managed_pages should be used
> @@ -527,6 +530,9 @@ struct zone {
> atomic_long_t managed_pages;
> unsigned long spanned_pages;
> unsigned long present_pages;
> +#ifdef CONFIG_CMA
> + unsigned long cma_pages;
> +#endif
>
> const char *name;
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b031a5ae0bd5..9a82375bbcb2 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -2168,6 +2168,7 @@ void __init init_cma_reserved_pageblock(struct page *page)
> }
>
> adjust_managed_page_count(page, pageblock_nr_pages);
> + page_zone(page)->cma_pages += pageblock_nr_pages;
> }
> #endif
>
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 7758486097f9..957680db41fa 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1650,6 +1650,11 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
> zone->spanned_pages,
> zone->present_pages,
> zone_managed_pages(zone));
> +#ifdef CONFIG_CMA
> + seq_printf(m,
> + "\n cma %lu",
> + zone->cma_pages);
> +#endif
>
> seq_printf(m,
> "\n protection: (%ld",
> --
> 2.29.2
>

--
Oscar Salvador
SUSE L3