linux-kernel - Re: [PATCH v3 2/2] mm: add docs for per-order mTHP split counters

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Message-ID: <40ba1239-bbe2-470b-8574-c7e098b40bc7@redhat.com>
Date: Fri, 5 Jul 2024 11:25:22 +0200
From: David Hildenbrand <david@...hat.com>
To: Ryan Roberts <ryan.roberts@....com>, Lance Yang <ioworker0@...il.com>,
 akpm@...ux-foundation.org
Cc: dj456119@...il.com, 21cnbao@...il.com, shy828301@...il.com,
 ziy@...dia.com, libang.li@...group.com, baolin.wang@...ux.alibaba.com,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 Barry Song <baohua@...nel.org>, Mingzhe Yang <mingzhe.yang@...com>
Subject: Re: [PATCH v3 2/2] mm: add docs for per-order mTHP split counters

On 05.07.24 11:16, Ryan Roberts wrote:
> On 04/07/2024 02:29, Lance Yang wrote:
>> This commit introduces documentation for mTHP split counters in
>> transhuge.rst.
>>
>> Reviewed-by: Barry Song <baohua@...nel.org>
>> Signed-off-by: Mingzhe Yang <mingzhe.yang@...com>
>> Signed-off-by: Lance Yang <ioworker0@...il.com>
>> ---
>>   Documentation/admin-guide/mm/transhuge.rst | 20 ++++++++++++++++----
>>   1 file changed, 16 insertions(+), 4 deletions(-)
>>
>> diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
>> index 1f72b00af5d3..0830aa173a8b 100644
>> --- a/Documentation/admin-guide/mm/transhuge.rst
>> +++ b/Documentation/admin-guide/mm/transhuge.rst
>> @@ -369,10 +369,6 @@ also applies to the regions registered in khugepaged.
>>   Monitoring usage
>>   ================
>>   
>> -.. note::
>> -   Currently the below counters only record events relating to
>> -   PMD-sized THP. Events relating to other THP sizes are not included.
>> -
>>   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
>> @@ -514,6 +510,22 @@ file_fallback_charge
>>   	falls back to using small pages even though the allocation was
>>   	successful.
>>   
>> +split
>> +	is incremented every time a huge page is successfully split into
>> +	smaller orders. This can happen for a variety of reasons but a
>> +	common reason is that a huge page is old and is being reclaimed.
>> +	This action implies splitting any block mappings into PTEs.
> 
> nit: the block mappings will already be PTEs if starting with mTHP?


Was confused by that as well, so maybe just drop that detail here.
-- 
Cheers,

David / dhildenb