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

David Hildenbrand
2021-01-28T22:05:40Z

> Am 28.01.2021 um 22:54 schrieb David Rientjes <rientjes@google.com>:
>
> ﻿On Thu, 28 Jan 2021, David Hildenbrand wrote:
>
>> 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",
>
> Hmm, not sure about this. If cma is only printed for CONFIG_CMA, we can't
> distinguish between (1) a kernel without your patch without including some
> version checking and (2) a kernel without CONFIG_CMA enabled. IOW,
> "cma 0" carries value: we know immediately that we do not have any CMA
> pages on this zone, period.
>
> /proc/zoneinfo is also not known for its conciseness so I think printing
> "cma 0" even for !CONFIG_CMA is helpful :)
>
> I think this #ifdef should be removed and it should call into a
> zone_cma_pages(struct zone *zone) which returns 0UL if disabled.
>

Yeah, that’s also what I proposed in a sub-thread here.

The last option would be going the full mile and not printing nr_free_cma. Code might get a bit uglier though, but we could also remove that stats counter ;)

I don‘t particularly care, while printing „0“ might be easier, removing nr_free_cma might be cleaner.

But then, maybe there are tools that expect that value to be around on any kernel?

Thoughts?

Thanks