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

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Date: Wed, 10 Apr 2024 18:07:51 +0200
From: Sumanth Korikkar <sumanthk@...ux.ibm.com>
To: David Hildenbrand <david@...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 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,
Sumanth