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

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Date: Wed, 10 Apr 2024 17:51:28 +0200
From: David Hildenbrand <david@...hat.com>
To: Sumanth Korikkar <sumanthk@...ux.ibm.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 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?

> 
> 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.

-- 
Cheers,

David / dhildenb