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

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Date: Wed, 24 Apr 2024 14:10:09 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: David Hildenbrand <david@...hat.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 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.