linux-kernel - Re: [PATCH] mm/shmem: Inline shmem_is_huge() for disabled transparent hugepages

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Message-ID: <79051196-601a-406c-9572-033173848bfb@redhat.com>
Date: Wed, 10 Apr 2024 19:03:21 +0200
From: David Hildenbrand <david@...hat.com>
To: Peter Xu <peterx@...hat.com>
Cc: Sumanth Korikkar <sumanthk@...ux.ibm.com>, akpm@...ux-foundation.org,
 linux-mm@...ck.org, hughd@...gle.com, hca@...ux.ibm.com, gor@...ux.ibm.com,
 agordeev@...ux.ibm.com, iii@...ux.ibm.com, linux-s390@...r.kernel.org,
 linux-kernel@...r.kernel.org, Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH] mm/shmem: Inline shmem_is_huge() for disabled transparent
 hugepages

On 10.04.24 18:51, Peter Xu wrote:
> On Wed, Apr 10, 2024 at 06:40:55PM +0200, David Hildenbrand wrote:
>> On 10.04.24 18:33, Peter Xu wrote:
>>> On Wed, Apr 10, 2024 at 06:12:34PM +0200, David Hildenbrand wrote:
>>>> On 10.04.24 18:07, Sumanth Korikkar wrote:
>>>>> On Wed, Apr 10, 2024 at 05:51:28PM +0200, David Hildenbrand wrote:
>>>>>> On 10.04.24 17:26, Sumanth Korikkar wrote:
>>>>>>> On Wed, Apr 10, 2024 at 02:34:35PM +0200, David Hildenbrand wrote:
>>>>>>>> On 09.04.24 17:54, Sumanth Korikkar wrote:
>>>>>>>>> In order to  minimize code size (CONFIG_CC_OPTIMIZE_FOR_SIZE=y),
>>>>>>>>> compiler might choose to make a regular function call (out-of-line) for
>>>>>>>>> shmem_is_huge() instead of inlining it. When transparent hugepages are
>>>>>>>>> disabled (CONFIG_TRANSPARENT_HUGEPAGE=n), it can cause compilation
>>>>>>>>> error.
>>>>>>>>>
>>>>>>>>> mm/shmem.c: In function ‘shmem_getattr’:
>>>>>>>>> ./include/linux/huge_mm.h:383:27: note: in expansion of macro ‘BUILD_BUG’
>>>>>>>>>        383 | #define HPAGE_PMD_SIZE ({ BUILD_BUG(); 0; })
>>>>>>>>>            |                           ^~~~~~~~~
>>>>>>>>> mm/shmem.c:1148:33: note: in expansion of macro ‘HPAGE_PMD_SIZE’
>>>>>>>>>       1148 |                 stat->blksize = HPAGE_PMD_SIZE;
>>>>>>>>>
>>>>>>>>> To prevent the possible error, always inline shmem_is_huge() when
>>>>>>>>> transparent hugepages are disabled.
>>>>>>>>>
>>>>>>>>
>>>>>>>> Do you know which commit introduced that?
>>>>>>> Hi David,
>>>>>>>
>>>>>>> Currently with CONFIG_CC_OPTIMIZE_FOR_SIZE=y and expirementing with
>>>>>>> -fPIC kernel compiler option, I could see this error on s390.
>>>>>>
>>>>>> Got it. I assume on Linus' tree, not mm/unstable?
>>>>>
>>>>> It's not yet upstream.
>>>>>>
>>>>>>>
>>>>>>> However, default kernel compiler options doesnt end up with the above
>>>>>>> pattern right now.
>>>>>>
>>>>>> Okay, just asking if this is related to recent HPAGE_PMD_SIZE changes:
>>>>>>
>>>>>> commit c1a1e497a3d5711dbf8fa6d7432d6b83ec18c26f
>>>>>> Author: Peter Xu <peterx@...hat.com>
>>>>>> Date:   Wed Mar 27 11:23:22 2024 -0400
>>>>>>
>>>>>>        mm: make HPAGE_PXD_* macros even if !THP
>>>>>>
>>>>>> Which is still in mm-unstable and not upstream.
>>>>>
>>>>> Not related to this commit. I tried on master branch.
>>>>
>>>> Thanks! Can you try with Peters patch? (ccing Peter)
>>>>
>>>> If I am not wrong, that should also resolve the issue you are seeing.
>>>
>>> David,
>>>
>>> Do you mean this one?
>>>
>>> https://lore.kernel.org/all/20240403013249.1418299-4-peterx@redhat.com/
>>>
>>
>> No, I meant:
>>
>> https://lore.kernel.org/all/20240327152332.950956-4-peterx@redhat.com/
>>
>> which removes the "#define HPAGE_PMD_SIZE ({ BUILD_BUG(); 0; })" that we
>> seem to trigger here.
>>
>>
>> ... but it's been a long day, so maybe I'm all wrong :)
> 
> Ah..  So I thought it was one step further. :)
> 
> Then that shouldn't be the case; it didn't remove it but defined properly
> with HPAGE_PMD_SHIFT:
> 
> +#define HPAGE_PMD_SIZE	((1UL) << HPAGE_PMD_SHIFT)
> 
> Now we even have that properly defined for HUGETLB_PAGE, while prior to
> that we should hit this issue easier (even with !THP+HUGETLB_PAGE).

Ah, now I spot

#define HPAGE_PMD_SHIFT ({ BUILD_BUG(); 0; })

:) sorry for the noise!

To the original patch here

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Cheers,

David / dhildenb