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

[Ryan Roberts <ryan.roberts@arm.com>]

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.