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

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Message-ID: <140d4efa-28a0-449a-9570-9d44c23b55d1@redhat.com>
Date: Wed, 24 Apr 2024 09:11:48 +0200
From: David Hildenbrand <david@...hat.com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>,
 Barry Song <21cnbao@...il.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 24.04.24 08:10, Baolin Wang wrote:
> 
> 
> On 2024/4/23 19:37, David Hildenbrand wrote:
>> 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.
> 
> Sure.
> 
>> ... 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.
> 
> Um, once we expose it to userspace through the sysfs interface, the
> sysfs interface should be explicit as much as possible and avoid
> confusing users, otherwise it will be difficult to change this kind of
> interface in the future. Personally, I prefer to Ryan's suggestion.

Inconsistency is confusing. As long as you avoid that, I don't 
particularly care.

-- 
Cheers,

David / dhildenb