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

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Date: Wed, 10 Apr 2024 18:12:34 +0200
From: David Hildenbrand <david@...hat.com>
To: Sumanth Korikkar <sumanthk@...ux.ibm.com>, Peter Xu <peterx@...hat.com>
Cc: 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
Subject: Re: [PATCH] mm/shmem: Inline shmem_is_huge() for disabled transparent
 hugepages

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.

-- 
Cheers,

David / dhildenb