linux-kernel - Re: [PATCH v3 0/6] add mTHP support for anonymous shmem

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Message-ID: <e7b4aaa1-170d-4500-bf7a-63672e4d81b8@linux.alibaba.com>
Date: Thu, 6 Jun 2024 11:31:01 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Daniel Gomez <da.gomez@...sung.com>
Cc: David Hildenbrand <david@...hat.com>,
 "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
 "hughd@...gle.com" <hughd@...gle.com>,
 "willy@...radead.org" <willy@...radead.org>,
 "wangkefeng.wang@...wei.com" <wangkefeng.wang@...wei.com>,
 "ying.huang@...el.com" <ying.huang@...el.com>,
 "21cnbao@...il.com" <21cnbao@...il.com>,
 "ryan.roberts@....com" <ryan.roberts@....com>,
 "shy828301@...il.com" <shy828301@...il.com>, "ziy@...dia.com"
 <ziy@...dia.com>, "ioworker0@...il.com" <ioworker0@...il.com>,
 Pankaj Raghav <p.raghav@...sung.com>, "linux-mm@...ck.org"
 <linux-mm@...ck.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 0/6] add mTHP support for anonymous shmem



On 2024/6/4 20:05, Daniel Gomez wrote:
> On Tue, Jun 04, 2024 at 05:45:20PM +0800, Baolin Wang wrote:
>>
>>
>> On 2024/6/4 16:18, Daniel Gomez wrote:
>>> On Fri, May 31, 2024 at 01:13:48PM +0200, David Hildenbrand wrote:
>>>>>>
>>>>>> As a default, we should not be using large folios / mTHP for any shmem,
>>>>>> just like we did with THP via shmem_enabled. This is what this series
>>>>>> currently does, and is aprt of the whole mTHP user-space interface design.
>>>>>>
>>>>>> Further, the mTHP controls should control all of shmem, not only
>>>>>> "anonymous shmem".
>>>>>
>>>>> Yes, that's what I thought and in my TODO list.
>>>>
>>>> Good, it would be helpful to coordinate with Daniel and Pankaj.
>>>
>>> I've integrated patches 11 and 12 from the lsf RFC thread [1] on top of Baolin's
>>> v3 patches. You may find a version in my integration branch here [2]. I can
>>> attach them here if it's preferred.
>>>
>>> [1] https://lore.kernel.org/all/20240515055719.32577-1-da.gomez@samsung.com/
>>> [2] https://protect2.fireeye.com/v1/url?k=a23e7c06-c3b56926-a23ff749-74fe485fb347-371ca2bfd5d9869f&q=1&e=6974304e-a786-4255-93a7-57498540241c&u=https%3A%2F%2Fgitlab.com%2Fdkruces%2Flinux-next%2F-%2Fcommits%2Fnext-20240604-shmem-mthp
>>>
>>> The point here is to combine the large folios strategy I proposed with mTHP
>>> user controls. Would it make sense to limit the orders to the mapping order
>>> calculated based on the size and index?
>>
>> IMO, for !anon shmem, this change makes sense to me. We should respect the
>> size and mTHP should act as a order filter.
> 
> What about respecing the size when within_size flag is enabled? Then, 'always'
> would allocate mTHP enabled folios, regardless of the size. And 'never'
> would ignore mTHP and size. So, 'never' can be used for this 'safe' boot case
> mentioned in the discussion.

Looks reasonable to me. What do you think, David?

And what about 'advise' option? Silimar to 'within_size'?

>> For anon shmem, we should ignore the length, which you always set it to
>> PAGE_SIZE in patch [1].
>>
>> [1] https://protect2.fireeye.com/v1/url?k=0d75a0c6-6cfeb5e6-0d742b89-74fe485fb347-904fa75c8efebdc2&q=1&e=6974304e-a786-4255-93a7-57498540241c&u=https%3A%2F%2Fgitlab.com%2Fdkruces%2Flinux-next%2F-%2Fcommit%2Fedf02311fd6d86b355d3aeb74e67c8da6de3c569
> 
> Since we are ignoring the length, we should ignore any value being passed.
> 
>>
>>> @@ -1765,6 +1798,10 @@ static struct folio *shmem_alloc_and_add_folio(struct vm_fault *vmf,
>>>
>>>                   order = highest_order(suitable_orders);
>>>                   while (suitable_orders) {
>>> +                       if (order > mapping_order) {
>>> +                               order = next_order(&suitable_orders, order);
>>> +                               continue;
>>> +                       }
>>>                           pages = 1UL << order;
>>>                           index = round_down(index, pages);
>>>                           folio = shmem_alloc_folio(gfp, order, info, index);
>>>
>>> Note: The branch still need to be adapted to include !anon mm.