Re: [PATCH v2] mm: thp: support "THPeligible" semantics for mTHP with anonymous shmem

["Bang Li" <libang.li@xxxxxxxxxxxx>]

Hi Ryan,

Thanks for the review!

On 2024/7/2 16:18, Ryan Roberts wrote:
> On 02/07/2024 03:34, Bang Li wrote:
> > After the commit 7fb1b252afb5 ("mm: shmem: add mTHP support for
> > anonymous shmem"), we can configure different policies through
> > the multi-size THP sysfs interface for anonymous shmem. But
> > currently "THPeligible" indicates only whether the mapping is
> > eligible for allocating THP-pages as well as the THP is PMD
> > mappable or not for anonymous shmem, we need to support semantics
> > for mTHP with anonymous shmem similar to those for mTHP with
> > anonymous memory.
> >
> > Signed-off-by: Bang Li <libang.li@xxxxxxxxxxxx>
> > ---
> > Changes since v1 [1]:
> >   - Put anonymous shmem mthp related logic into
> >     thp_vma_allowable_orders() (per David)
> >
> > [1] https://lore.kernel.org/linux-mm/20240628104926.34209-1-libang.li@xxxxxxxxxxxx/
> > ---
> >   include/linux/huge_mm.h | 11 +++++++++++
> >   mm/huge_memory.c        | 13 +++++++++----
> >   mm/shmem.c              |  9 +--------
> >   3 files changed, 21 insertions(+), 12 deletions(-)
> >
> > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> > index 212cca384d7e..f87136f38aa1 100644
> > --- a/include/linux/huge_mm.h
> > +++ b/include/linux/huge_mm.h
> > @@ -267,6 +267,10 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
> >   	return __thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders);
> >   }
> >   
> > +unsigned long shmem_allowable_huge_orders(struct inode *inode,
> > +				struct vm_area_struct *vma, pgoff_t index,
> > +				bool global_huge);
> > +
> >   struct thpsize {
> >   	struct kobject kobj;
> >   	struct list_head node;
> > @@ -460,6 +464,13 @@ static inline unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
> >   	return 0;
> >   }
> >   
> > +static inline unsigned long shmem_allowable_huge_orders(struct inode *inode,
> > +				struct vm_area_struct *vma, pgoff_t index,
> > +				bool global_huge)
> > +{
> > +	return 0;
> > +}
> > +
> >   #define transparent_hugepage_flags 0UL
> >   
> >   #define thp_get_unmapped_area	NULL
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index c7ce28f6b7f3..ea377bb4af91 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -151,10 +151,15 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
> >   	 * Must be done before hugepage flags check since shmem has its
> >   	 * own flags.
> >   	 */
> > -	if (!in_pf && shmem_file(vma->vm_file))
> > -		return shmem_is_huge(file_inode(vma->vm_file), vma->vm_pgoff,
> > -				     !enforce_sysfs, vma->vm_mm, vm_flags)
> > -			? orders : 0;
> > +	if (!in_pf && shmem_file(vma->vm_file)) {
> > +		bool global_huge = shmem_is_huge(file_inode(vma->vm_file), vma->vm_pgoff,
> > +							!enforce_sysfs, vma->vm_mm, vm_flags);
> > +
> > +		if (!vma_is_anon_shmem(vma))
> > +			return global_huge? orders : 0;
>
> nit: missing space before '?'

Yes, thanks.

> > +		return shmem_allowable_huge_orders(file_inode(vma->vm_file),
> > +							vma, vma->vm_pgoff, global_huge);
>
> What's the rationale for splitting these functions into shmem_is_huge() and
> shmem_allowable_huge_orders()? Why not just have a single
> shmem_allowable_huge_orders() that tells you the answer?

Currently, shmem_is_huge() is used for all shmem implementations to 
determine whether the conditions for using THP are met. And 
shmem_allowable_huge_orders() is currently mainly used for anonymous 
shmem's mTHP to obtain all orders that meet the conditions. In my 
opinion, there is no problem in separating these two functions. In the 
future, when mTHP of other shmem types is also implemented, will 
shmem_is_huge() be unnecessary?

Thanks,
Bang

> > +	}
> >   
> >   	if (!vma_is_anonymous(vma)) {
> >   		/*
> > diff --git a/mm/shmem.c b/mm/shmem.c
> > index d495c0701a83..aa85df9c662a 100644
> > --- a/mm/shmem.c
> > +++ b/mm/shmem.c
> > @@ -1622,7 +1622,7 @@ static gfp_t limit_gfp_mask(gfp_t huge_gfp, gfp_t limit_gfp)
> >   }
> >   
> >   #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > -static unsigned long shmem_allowable_huge_orders(struct inode *inode,
> > +unsigned long shmem_allowable_huge_orders(struct inode *inode,
> >   				struct vm_area_struct *vma, pgoff_t index,
> >   				bool global_huge)
> >   {
> > @@ -1707,13 +1707,6 @@ static unsigned long shmem_suitable_orders(struct inode *inode, struct vm_fault
> >   	return orders;
> >   }
> >   #else
> > -static unsigned long shmem_allowable_huge_orders(struct inode *inode,
> > -				struct vm_area_struct *vma, pgoff_t index,
> > -				bool global_huge)
> > -{
> > -	return 0;
> > -}
> > -
> >   static unsigned long shmem_suitable_orders(struct inode *inode, struct vm_fault *vmf,
> >   					   struct address_space *mapping, pgoff_t index,
> >   					   unsigned long orders)