From: David Hildenbrand <david@redhat.com>
To: David Rientjes <rientjes@google.com>
Cc: David Hildenbrand <david@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Mike Rapoport <rppt@kernel.org>,
Oscar Salvador <osalvador@suse.de>,
Michal Hocko <mhocko@kernel.org>,
Wei Yang <richard.weiyang@linux.alibaba.com>,
linux-api@vger.kernel.org
Subject: Re: [PATCH v2] mm/page_alloc: count CMA pages per zone and print them in /proc/zoneinfo
Date: Thu, 28 Jan 2021 23:30:33 +0100 [thread overview]
Message-ID: <2CF5220A-5452-4913-AFCB-41E1C642E521@redhat.com> (raw)
In-Reply-To: <89e1dbcd-605d-6a7b-361-c130f7eb9d8c@google.com>
> Am 28.01.2021 um 23:28 schrieb David Rientjes <rientjes@google.com>:
>
> On Thu, 28 Jan 2021, David Hildenbrand wrote:
>
>>> 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.
>>
>
> Ah, I certainly think your original intuition was correct.
>
>> 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?
>>
>
> Yeah, that's probably undue risk, the ship has sailed and there's no
> significant upside.
>
> I still think "cma 0" in /proc/zoneinfo carries value, though, especially
> for NUMA and it looks like this is how it's done in linux-next. With a
> single read of the file, userspace can make the determination what CMA
> pages exist on this node.
>
> In general, I think the rule-of-thumb is that the fewer ifdefs in
> /proc/zoneinfo, the easier it is for userspace to parse it.
Makes sense, I‘ll send an updated version tomorrow - thanks!
>
> (I made that change to /proc/zoneinfo to even print non-existant zones for
> each node because otherwise you cannot determine what the indices of
> things like vm.lowmem_reserve_ratio represent.)
next prev parent reply other threads:[~2021-01-28 22:30 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-27 10:18 [PATCH v1 0/2] mm/cma: better error handling and count pages per zone David Hildenbrand
2021-01-27 10:18 ` [PATCH v1 1/2] mm/cma: expose all pages to the buddy if activation of an area fails David Hildenbrand
2021-01-27 15:58 ` Zi Yan
2021-01-28 9:59 ` Oscar Salvador
2021-01-27 10:18 ` [PATCH v1 2/2] mm/page_alloc: count CMA pages per zone and print them in /proc/zoneinfo David Hildenbrand
2021-01-28 10:22 ` Oscar Salvador
2021-01-28 10:43 ` David Hildenbrand
2021-01-28 13:44 ` Oscar Salvador
2021-01-28 13:46 ` Oscar Salvador
2021-01-28 14:01 ` David Hildenbrand
2021-01-28 16:45 ` [PATCH v2] " David Hildenbrand
2021-01-28 21:42 ` Oscar Salvador
2021-01-28 21:54 ` David Rientjes
2021-01-28 22:03 ` David Hildenbrand
2021-01-28 22:28 ` David Rientjes
2021-01-28 22:30 ` David Hildenbrand [this message]
2021-01-29 11:34 ` [PATCH v3] " David Hildenbrand
2021-01-29 11:46 ` Oscar Salvador
2021-01-29 11:51 ` David Hildenbrand
2021-01-30 8:48 ` David Rientjes
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