linux-kernel - Re: [PATCH v2 0/2] mm: collect the number of anon mTHP

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Message-ID: <b5f8448a-daf2-44d7-bcad-b66ff2908e63@gmail.com>
Date: Mon, 19 Aug 2024 10:22:44 -0400
From: Usama Arif <usamaarif642@...il.com>
To: Barry Song <21cnbao@...il.com>, David Hildenbrand <david@...hat.com>,
 akpm@...ux-foundation.org
Cc: linux-mm@...ck.org, baolin.wang@...ux.alibaba.com, chrisl@...nel.org,
 hanchuanhua@...o.com, ioworker0@...il.com, kaleshsingh@...gle.com,
 kasong@...cent.com, linux-kernel@...r.kernel.org, ryan.roberts@....com,
 v-songbaohua@...o.com, ziy@...dia.com, yuanshuai@...o.com
Subject: Re: [PATCH v2 0/2] mm: collect the number of anon mTHP



On 19/08/2024 09:52, Barry Song wrote:
> On Mon, Aug 19, 2024 at 8:33 PM Barry Song <21cnbao@...il.com> wrote:
>>
>> On Mon, Aug 19, 2024 at 8:28 PM David Hildenbrand <david@...hat.com> wrote:
>>>
>>> On 18.08.24 09:58, Barry Song wrote:
>>>> Hi Andrew, David, Usama,
>>>>
>>>> I'm attempting to rebase this series on top of Usama's
>>>> [PATCH v3 0/6] mm: split underutilized THPs[1]
>>>>
>>>> However, I feel it is impossible and we might be tackling things
>>>> in the wrong order.
>>>
>>> Is just the ordering suboptimal (which can/will get resolved one way or
>>> the other), or is there something fundamental that will make this series
>>> here "impossible"?
>>
>> i think it is just the ordering suboptimal. Ideally, mTHP counters can go
>> first, then the new partially_mapped feature will rebase on top of
>> mTHP counters.
> 
> Sorry, please allow me to ramble a bit more.
> 
> The nr_split_deferred counter is straightforward and simple without the
> partially_mapped feature. Each time we enter split_list, we increment by
> 1, and when we leave, we decrement by 1.
> 
> With the new partially_mapped feature, we can enter split_list without
> actually being partially_mapped. If the MTHP counter series is processed
> first, the partially_mapped series can handle all cases while properly
> clearing and setting the partially_mapped flag. These flag operations
> need to be handled carefully.
> Currently, I notice that Usama's series is clearing the flag unconditionally
> in all cases.
> 
> In simple terms, mTHP counters are just a counting mechanism that
> doesn't introduce new features. However, partially_mapped is a new
> feature. A better approach might be to handle the counters first, then
> ensure that the new feature doesn't break the counter.
> 

I am ok if the series needs to be reversed, I think the difficulty is for Andrew to tackle my series, yours and Yu Zhaos, which all seem to be touching the same code, so whatever makes it easier for Andrew I am happy with it.


>>
>>>
>>> --
>>> Cheers,
>>>
>>> David / dhildenb
> 
> Thanks
> Barry