Re: [PATCH mm-unstable v3 01/10] mm/shmem: add flag to enforce shmem THP in hugepage_vma_check()

[Yang Shi <shy828301@gmail.com>]

On Wed, Sep 7, 2022 at 7:45 AM Zach O'Keefe <zokeefe@google.com> wrote:
>
> Extend 'mm/thp: add flag to enforce sysfs THP in
> hugepage_vma_check()' to shmem, allowing callers to ignore
> /sys/kernel/transparent_hugepage/shmem_enabled and tmpfs huge= mount.
>
> This is intended to be used by MADV_COLLAPSE, and the rationale is
> analogous to the anon/file case: MADV_COLLAPSE is not coupled to
> directives that advise the kernel's decisions on when THPs should be
> considered eligible. shmem/tmpfs always claims large folio support,
> regardless of sysfs or mount options.
>
> Signed-off-by: Zach O'Keefe <zokeefe@google.com>

Reviewed-by: Yang Shi <shy828301@gmail.com>

A nit below...

> ---
>  include/linux/shmem_fs.h | 10 ++++++----
>  mm/huge_memory.c         |  2 +-
>  mm/shmem.c               | 18 +++++++++---------
>  3 files changed, 16 insertions(+), 14 deletions(-)
>
> diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
> index f24071e3c826..d500ea967dc7 100644
> --- a/include/linux/shmem_fs.h
> +++ b/include/linux/shmem_fs.h
> @@ -92,11 +92,13 @@ extern struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
>  extern void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end);
>  int shmem_unuse(unsigned int type);
>
> -extern bool shmem_is_huge(struct vm_area_struct *vma,
> -                         struct inode *inode, pgoff_t index);
> -static inline bool shmem_huge_enabled(struct vm_area_struct *vma)
> +extern bool shmem_is_huge(struct vm_area_struct *vma, struct inode *inode,
> +                         pgoff_t index, bool shmem_huge_force);
> +static inline bool shmem_huge_enabled(struct vm_area_struct *vma,
> +                                     bool shmem_huge_force)
>  {
> -       return shmem_is_huge(vma, file_inode(vma->vm_file), vma->vm_pgoff);
> +       return shmem_is_huge(vma, file_inode(vma->vm_file), vma->vm_pgoff,
> +                            shmem_huge_force);
>  }
>  extern unsigned long shmem_swap_usage(struct vm_area_struct *vma);
>  extern unsigned long shmem_partial_swap_usage(struct address_space *mapping,
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 7fa74b9749a6..53d170dac332 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -119,7 +119,7 @@ bool hugepage_vma_check(struct vm_area_struct *vma, unsigned long vm_flags,
>          * own flags.
>          */
>         if (!in_pf && shmem_file(vma->vm_file))
> -               return shmem_huge_enabled(vma);
> +               return shmem_huge_enabled(vma, !enforce_sysfs);
>
>         /* Enforce sysfs THP requirements as necessary */
>         if (enforce_sysfs &&
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 99b7341bd0bf..47c42c566fd1 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -461,20 +461,20 @@ static bool shmem_confirm_swap(struct address_space *mapping,
>
>  static int shmem_huge __read_mostly = SHMEM_HUGE_NEVER;
>
> -bool shmem_is_huge(struct vm_area_struct *vma,
> -                  struct inode *inode, pgoff_t index)
> +bool shmem_is_huge(struct vm_area_struct *vma, struct inode *inode,
> +                  pgoff_t index, bool shmem_huge_force)
>  {
>         loff_t i_size;
>
>         if (!S_ISREG(inode->i_mode))
>                 return false;
> -       if (shmem_huge == SHMEM_HUGE_DENY)
> -               return false;
>         if (vma && ((vma->vm_flags & VM_NOHUGEPAGE) ||
>             test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags)))
>                 return false;
> -       if (shmem_huge == SHMEM_HUGE_FORCE)
> +       if (shmem_huge == SHMEM_HUGE_FORCE || shmem_huge_force)

shmem_huge_force means ignore all sysfs and mount options, so it seems
better to have it test explicitly IMHO, like:

if (shmem_huge_force)
    return true;

if (shmem_huge == SHMEM_HUGE_FORCE)
    return true;


>                 return true;
> +       if (shmem_huge == SHMEM_HUGE_DENY)
> +               return false;
>
>         switch (SHMEM_SB(inode->i_sb)->huge) {
>         case SHMEM_HUGE_ALWAYS:
> @@ -669,8 +669,8 @@ static long shmem_unused_huge_count(struct super_block *sb,
>
>  #define shmem_huge SHMEM_HUGE_DENY
>
> -bool shmem_is_huge(struct vm_area_struct *vma,
> -                  struct inode *inode, pgoff_t index)
> +bool shmem_is_huge(struct vm_area_struct *vma, struct inode *inode,
> +                  pgoff_t index, bool shmem_huge_force)
>  {
>         return false;
>  }
> @@ -1056,7 +1056,7 @@ static int shmem_getattr(struct user_namespace *mnt_userns,
>                         STATX_ATTR_NODUMP);
>         generic_fillattr(&init_user_ns, inode, stat);
>
> -       if (shmem_is_huge(NULL, inode, 0))
> +       if (shmem_is_huge(NULL, inode, 0, false))
>                 stat->blksize = HPAGE_PMD_SIZE;
>
>         if (request_mask & STATX_BTIME) {
> @@ -1888,7 +1888,7 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
>                 return 0;
>         }
>
> -       if (!shmem_is_huge(vma, inode, index))
> +       if (!shmem_is_huge(vma, inode, index, false))
>                 goto alloc_nohuge;
>
>         huge_gfp = vma_thp_gfp_mask(vma);
> --
> 2.37.2.789.g6183377224-goog
>