Re: [RFC] perf tools: Add hugetlbfs memory recognition

Hou Pengyang
2015-06-30T09:34:13Z

On 2015/6/29 21:42, Arnaldo Carvalho de Melo wrote:
> Em Mon, Jun 29, 2015 at 10:23:29AM -0300, Arnaldo Carvalho de Melo escreveu:
>> Em Sat, Jun 27, 2015 at 05:08:20PM +0800, Hou Pengyang escreveu:
>>> There is something about MAP_HUGETLB.
>>
>>> In this patch, we check if a mmap area is hugetlbfs area by MAP_HUGETLB,
>>> a bit in MMAP2 event.
>>
>>> However, if mmap area is hugetlb related, MAP_HUGETLB does not always
>>> appear. Because, there are two ways generating MMAP2 event.
>>
>>> 1) when a new vm_area_struct is created, its info would be exported
>>> as a MMAP2 event.
>>> 2) perf reads /proc/pid/maps for generating MMAP2 event.
>>
>>> MAP_HUGETLB appears if MMAP2 event is generated on situation 1),
>>> while not on situation 2).
>>
>>> This is because on situation 2), perf reads /proc/pid/maps, which
>>> contains only PROT_READ/WRITE/EXEC, MAP_SHARED/MAP_PRIVATE, while more
>>> details appear in /proc/pid/smaps, such as MAP_HUGETLB.
>>
>> Humm:
>>
>> [root@zoo ~]# wc -l /proc/`pidof firefox`/maps
>> 934 /proc/4551/maps
>> [root@zoo ~]# wc -l /proc/`pidof firefox`/smaps
>> 14944 /proc/4551/smaps
>> [root@zoo ~]#
>>
>>> So I wonder if there is a need to read /proc/pid/smaps instead of
>>> /proc/pid/maps to generate MMAP2 event. Or we should solve the problem by
>>> another way?
>>
>> Doing some research now...
>
> Bummer, seems that only smaps -> ... -> show_smap_vma_flags() will
> expose that to userspace...
>
> Perhaps we can look at some global stat for HugeTLB fs to figure out if
> we really, really need to parse smaps instead of just maps? I.e. in my
> system, a desktop one, F21, I have:
>

It seems no other info tell us if one process is using hugetlbfs.
So how about an option to tell perf explicitly which file is from
hugetlbfs, like:

./perf report --hugetlb-file=/mnt/huge/hugepagefile

So that, we can check if a mmap area is from hugetlbfs by its name
instead of MAP_HUGETLB.

> [root@zoo ~]# find /proc -name smaps | xargs grep -w ht
> grep: /proc/31971/task/31971/smaps: No such file or directory
> grep: /proc/31971/smaps: No such file or directory
> [root@zoo ~]#
>
> No "ht" HugeTLB areas, so no need to parse 16 times more bytes than by
> just using /proc/PID/maps.

>
> - Arnaldo
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