Re: [PATCH v1 2/2] mm/page_alloc: count CMA pages per zone and print them in /proc/zoneinfo

Oscar Salvador
2021-01-28T10:24:32Z

On Wed, Jan 27, 2021 at 11:18:13AM +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 (e.g., like
> ZONE_MOVABLE) - even after some of these pages might already have been
> allocated.

My knowledge of CMA tends to be quite low, actually I though that CMA
was somehow tied to ZONE_MOVABLE.

I see how tracking CMA pages per zona might give you a clue, but what do
you mean by "might behave differently - even after some of these pages might
already have been allocated"

> 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.
>
> Note: Track/print that information even without CONFIG_CMA, similar to
> "nr_free_cma" in /proc/zoneinfo. This is different to /proc/meminfo -
> maybe we want to make that consistent in the future (however, changing
> /proc/zoneinfo output might uglify the code a bit).
> 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>
> Signed-off-by: David Hildenbrand <david@redhat.com>
> ---
> include/linux/mmzone.h | 4 ++++
> mm/page_alloc.c | 1 +
> mm/vmstat.c | 6 ++++--
> 3 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index ae588b2f87ef..3bc18c9976fd 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 +530,7 @@ struct zone {
> atomic_long_t managed_pages;
> unsigned long spanned_pages;
> unsigned long present_pages;
> + unsigned long cma_pages;

I see that NR_FREE_CMA_PAGES is there even without CONFIG_CMA, as you
said, but I am not sure about adding size to a zone unconditionally.
I mean, it is not terrible as IIRC, the maximum MAX_NUMNODES can get
is 1024, and on x86_64 that would be (1024 * 4 zones) * 8 = 32K.
So not a big deal, but still.

Besides following NR_FREE_CMA_PAGES, is there any reason for not doing:

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 1e22d96734e0..2d8a830d168d 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -436,6 +436,9 @@ struct zone {
unsigned long 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/vmstat.c b/mm/vmstat.c
index 8ba0870ecddd..5757df4bfd45 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1559,13 +1559,15 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
"\n spanned %lu"
"\n present %lu"
"\n managed %lu",
+ "\n cma %lu",
zone_page_state(zone, NR_FREE_PAGES),
min_wmark_pages(zone),
low_wmark_pages(zone),
high_wmark_pages(zone),
zone->spanned_pages,
zone->present_pages,
- zone->managed_pages);
+ zone->managed_pages,
+ IS_ENABLED(CONFIG_CMA) ? zone->cma_pages : 0);

seq_printf(m,
"\n protection: (%ld",

I do not see it that ugly, but just my taste.

--
Oscar Salvador
SUSE L3