Re: [PATCH] smaps: count large pages smaller than PMD size to anonymous_thp

[Dev Jain <dev.jain@arm.com>]

On 16/12/24 9:28 pm, Wenchao Hao wrote:
> On 2024/12/5 1:05, Ryan Roberts wrote:
>> On 04/12/2024 14:40, Wenchao Hao wrote:
>>> On 2024/12/3 22:42, Ryan Roberts wrote:
>>>> On 03/12/2024 14:17, David Hildenbrand wrote:
>>>>> On 03.12.24 14:49, Wenchao Hao wrote:
>>>>>> Currently, /proc/xxx/smaps reports the size of anonymous huge pages for
>>>>>> each VMA, but it does not include large pages smaller than PMD size.
>>>>>>
>>>>>> This patch adds the statistics of anonymous huge pages allocated by
>>>>>> mTHP which is smaller than PMD size to AnonHugePages field in smaps.
>>>>>>
>>>>>> Signed-off-by: Wenchao Hao <haowenchao22@gmail.com>
>>>>>> ---
>>>>>>    fs/proc/task_mmu.c | 6 ++++++
>>>>>>    1 file changed, 6 insertions(+)
>>>>>>
>>>>>> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
>>>>>> index 38a5a3e9cba2..b655011627d8 100644
>>>>>> --- a/fs/proc/task_mmu.c
>>>>>> +++ b/fs/proc/task_mmu.c
>>>>>> @@ -717,6 +717,12 @@ static void smaps_account(struct mem_size_stats *mss,
>>>>>> struct page *page,
>>>>>>            if (!folio_test_swapbacked(folio) && !dirty &&
>>>>>>                !folio_test_dirty(folio))
>>>>>>                mss->lazyfree += size;
>>>>>> +
>>>>>> +        /*
>>>>>> +         * Count large pages smaller than PMD size to anonymous_thp
>>>>>> +         */
>>>>>> +        if (!compound && PageHead(page) && folio_order(folio))
>>>>>> +            mss->anonymous_thp += folio_size(folio);
>>>>>>        }
>>>>>>          if (folio_test_ksm(folio))
>>>>>
>>>>> I think we decided to leave this (and /proc/meminfo) be one of the last
>>>>> interfaces where this is only concerned with PMD-sized ones:
>>>>>
>>>>> Documentation/admin-guide/mm/transhuge.rst:
>>>>>
>>>>> The number of PMD-sized anonymous transparent huge pages currently used by the
>>>>> system is available by reading the AnonHugePages field in ``/proc/meminfo``.
>>>>> To identify what applications are using PMD-sized anonymous transparent huge
>>>>> pages, it is necessary to read ``/proc/PID/smaps`` and count the AnonHugePages
>>>>> fields for each mapping. (Note that AnonHugePages only applies to traditional
>>>>> PMD-sized THP for historical reasons and should have been called
>>>>> AnonHugePmdMapped).
>>>>>
>>>> Agreed. If you need per-process metrics for mTHP, we have a python script at
>>>> tools/mm/thpmaps which does a fairly good job of parsing pagemap. --help gives
>>>> you all the options.
>>>>
>>> I tried this tool, and it is very powerful and practical IMO.
>>> However, thereare two disadvantages:
>>>
>>> - This tool is heavily dependent on Python and Python libraries.
>>>    After installing several libraries with the pip command, I was able to
>>>    get it running.
>> I think numpy is the only package it uses which is not in the standard library?
>> What other libraries did you need to install?
>>
> Yes, I just tested it on the standard version (Fedora), and that is indeed the case.
> Previously, I needed to install additional packages is because I removed some unused
> software from the old environment.
>
> Recently, I revisited and started using your tool again. It’s very useful, meeting
> my needs and even exceeding them. I am now testing with qemu to run a fedora, so
> it's easy to run it.
>
>>>    In practice, the environment we need to analyze may be a mobile or
>>>    embedded environment, where it is very difficult to deploy these
>>>    libraries.
>> Yes, I agree that's a problem, especially for Android. The script has proven
>> useful to me for debugging in a traditional Linux distro environment though.
>>
>>> - It seems that this tool only counts file-backed large pages? During
>> No; the tool counts file-backed and anon memory. But it reports it in separate
>> counters. See `thpmaps --help` for full details.
>>
>>>    the actual test, I mapped a region of anonymous pages and mapped it
>>>    as large pages, but the tool did not display those large pages.
>>>    Below is my test file(mTHP related sysfs interface is set to "always"
>>>    to make sure using large pages):
>> Which mTHP sizes did you enable? Depending on your value of SIZE and which mTHP
>> sizes are enabled, you may not have a correctly aligned region in p. So mTHP
>> would not be allocated. Best to over-allocate then explicitly align p to the
>> mTHP size, then fault it in.
>>
> I enabled 64k/128k/256k MTHP and have been studying, debugging, and changing
> parts of the khugepaged code to try merging standard pages into mTHP large
> pages. So, I wanted to use smap to observe the large page sizes in a process.

You can try my RFC khugepaged series for that ;)

>
>>> int main()
>>> {
>>>          int i;
>>>          char *c;
>>>          unsigned long *p;
>>>
>>>          p = mmap(NULL, SIZE, PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
>> What is SIZE here?
>>
>>>          if (!p) {
>>>                  perror("fail to get memory");
>>>                  exit(-1);
>>>          }
>>>
>>>          c = (unsigned char *)p;
>>>
>>>          for (i = 0; i < SIZE / 8; i += 8)
>>>                  *(p + i) = 0xffff + i;
>> Err... what's your intent here? I think you're writting to 1 in every 8 longs?
>> Probably just write to the first byte of every page.
>>
> The data is fixed for the purpose of analyzing zram compression, so I filled
> some data here.
>
>> Thanks,
>> Ryan
>>
>>>          while (1)
>>>                  sleep(10);
>>>
>>>          return 0;
>>> }
>>>
>>> Thanks,
>>> wenchao
>>>
>