Re: [PATCH v2] fixup: mm/huge_memory.c: introduce folio_split_unmapped

David Hildenbrand (Red Hat)
2025-11-20T16:21:55Z

On 11/20/25 14:42, Balbir Singh wrote:
> Code refactoring of __folio_split() via helper
> __folio_freeze_and_split_unmapped() caused a regression with clang-20
> with CONFIG_SHMEM=n, the compiler was not able to optimize away the
> call to shmem_uncharge() due to changes in nr_shmem_dropped.
> Fix this by adding a stub function for shmem_uncharge when
> CONFIG_SHMEM is not defined.
>
> smatch also complained about parameter end being used without
> initialization, which is a false positive, but keep the tool happy
> by sending in initialized parameters. end is initialized to 0.
> smatch still complains about mapping being NULL and nr_shmem_dropped
> may not be 0, but that is not true prior to or after the changes.
>
> Add detailed documentation comments for folio_split_unmapped()
>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Zi Yan <ziy@nvidia.com>
> Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
> Cc: Rakie Kim <rakie.kim@sk.com>
> Cc: Byungchul Park <byungchul@sk.com>
> Cc: Gregory Price <gourry@gourry.net>
> Cc: Ying Huang <ying.huang@linux.alibaba.com>
> Cc: Alistair Popple <apopple@nvidia.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
> Cc: "Liam R. Howlett" <Liam.Howlett@oracle.com>
> Cc: Nico Pache <npache@redhat.com>
> Cc: Ryan Roberts <ryan.roberts@arm.com>
> Cc: Dev Jain <dev.jain@arm.com>
> Cc: Barry Song <baohua@kernel.org>
> Cc: Lyude Paul <lyude@redhat.com>
> Cc: Danilo Krummrich <dakr@kernel.org>
> Cc: David Airlie <airlied@gmail.com>
> Cc: Simona Vetter <simona@ffwll.ch>
> Cc: Ralph Campbell <rcampbell@nvidia.com>
> Cc: Mika Penttilä <mpenttil@redhat.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: Francois Dugast <francois.dugast@intel.com>
>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Balbir Singh <balbirs@nvidia.com>
> ---
> This fixup should be squashed into the patch "mm/huge_memory.c:
> introduce folio_split_unmapped" in mm/mm-unstable
>
> include/linux/shmem_fs.h | 6 +++++-
> mm/huge_memory.c | 30 +++++++++++++++++++++---------
> 2 files changed, 26 insertions(+), 10 deletions(-)
>
> diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> index 5b368f9549d6..7a412dd6eb4f 100644
> --- a/include/linux/shmem_fs.h
> +++ b/include/linux/shmem_fs.h
> @@ -136,11 +136,16 @@ static inline bool shmem_hpage_pmd_enabled(void)
>
> #ifdef CONFIG_SHMEM
> extern unsigned long shmem_swap_usage(struct vm_area_struct *vma);
> +extern void shmem_uncharge(struct inode *inode, long pages);

I forgot to add, we drop the "extern" on functions whenever we move them.

> #else
> static inline unsigned long shmem_swap_usage(struct vm_area_struct *vma)
> {
> return 0;
> }
> +
> +static void shmem_uncharge(struct inode *inode, long pages)

"static inline void" should resolve the compilation issue.

--
Cheers

David