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

[Zach O'Keefe <zokeefe@google.com>]

On Sep 16 10:46, Yang Shi wrote:
> 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...
> 

Hey Yang,

Thanks for taking the time as always :)

> > ---
> >  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;
> 
> 

This makes sense to me - a little bit cleaner / more direct.  Thanks for the
suggestion.

Thank you again,
Zach

> >                 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
> >