Re: [PATCH v3] mm/page_alloc: count CMA pages per zone and print them in /proc/zoneinfo

[David Hildenbrand <david@redhat.com>]

On 29.01.21 12:46, Oscar Salvador wrote:
> On Fri, Jan 29, 2021 at 12:34:51PM +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 print even without CONFIG_CMA, just like "nr_free_cma"; this way,
>>        one can be sure when spotting "cma 0", that there are definetly no
>>        CMA pages located in a zone.
>>
>> 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: David Rientjes <rientjes@google.com>
>> Cc: linux-api@vger.kernel.org
>> Signed-off-by: David Hildenbrand <david@redhat.com>
> 
> Looks good to me, I guess it is better to print it unconditionally
> so the layout does not change.
> 
> Reviewed-by: Oscar Salvador <osalvador@suse.de>

Thanks for the fast review!


-- 
Thanks,

David / dhildenb