linux-kernel - Re: [RFC PATCH 5/5] mm: shmem: add anonymous share mTHP counters

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Message-ID: <ce6be451-7c5a-402f-8340-be40699829c2@redhat.com>
Date: Tue, 23 Apr 2024 13:37:58 +0200
From: David Hildenbrand <david@...hat.com>
To: Barry Song <21cnbao@...il.com>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: akpm@...ux-foundation.org, hughd@...gle.com, willy@...radead.org,
 wangkefeng.wang@...wei.com, ryan.roberts@....com, ying.huang@...el.com,
 shy828301@...il.com, ziy@...dia.com, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 5/5] mm: shmem: add anonymous share mTHP counters

On 23.04.24 03:17, Barry Song wrote:
> On Mon, Apr 22, 2024 at 3:03 PM Baolin Wang
> <baolin.wang@...ux.alibaba.com> wrote:
>>
>> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
>> ---
>>   include/linux/huge_mm.h | 2 ++
>>   mm/huge_memory.c        | 4 ++++
>>   mm/shmem.c              | 5 ++++-
>>   3 files changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
>> index 26b6fa98d8ac..67b9c1acad31 100644
>> --- a/include/linux/huge_mm.h
>> +++ b/include/linux/huge_mm.h
>> @@ -270,6 +270,8 @@ enum mthp_stat_item {
>>          MTHP_STAT_ANON_SWPOUT,
>>          MTHP_STAT_ANON_SWPOUT_FALLBACK,
>>          MTHP_STAT_ANON_SWPIN_REFAULT,
>> +       MTHP_STAT_SHMEM_ANON_ALLOC,
>> +       MTHP_STAT_SHMEM_ANON_ALLOC_FALLBACK,
> 
> not quite sure about this. for 2MB pmd-mapped THP shmem, we count them
> as FILE_THP.
> here we are counting as SHMEM_ANON. To me, SHMEM_ANON is more correct but
> it doesn't align with pmd-mapped THP. David, Ryan, what do you think?

The term "anonymous share" in the patch subject is weird to begin with 
;) Easy to confuse with anonymous cow-shared memory. Let's just call it 
"anonymous shmem", which it is under the hood.

.. regarding the question: if we add FILE_ALLOC and friends, at least 
initially, we wouldn't account other large pagecache folios.

.. likely we should add that then as well so the counter matches the 
actual name?

If we later realize that we need separate FILE vs. SHMEM vs. WHATEVER 
counters, we can always add more fine-grained counters later. Doing it 
consistently w.r.t. traditional THPs first sounds reasonable.

-- 
Cheers,

David / dhildenb