[PATCH v4 22/66] mm: Use maple tree operations for find_vma_intersection() and find_vma()

[Liam Howlett]

* Vlastimil Babka <vbabka at suse.cz> [220113 10:53]:
> On 12/1/21 15:29, Liam Howlett wrote:
> > From: "Liam R. Howlett" <Liam.Howlett at Oracle.com>
> > 
> > Move find_vma_intersection() to mmap.c and change implementation to
> > maple tree.
> > 
> > When searching for a vma within a range, it is easier to use the maple
> > tree interface.  This means the find_vma() call changes to a special
> > case of the find_vma_intersection().
> > 
> > Exported for kvm module.
> > 
> > Signed-off-by: Liam R. Howlett <Liam.Howlett at Oracle.com>
> > ---
> >  include/linux/mm.h | 25 ++++++-------------------
> >  mm/mmap.c          | 38 ++++++++++++++++++++++++++++----------
> >  2 files changed, 34 insertions(+), 29 deletions(-)
> > 
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index c08f6d541b8a..39a947f29f6d 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -2812,26 +2812,13 @@ extern struct vm_area_struct * find_vma(struct mm_struct * mm, unsigned long add
> >  extern struct vm_area_struct * find_vma_prev(struct mm_struct * mm, unsigned long addr,
> >  					     struct vm_area_struct **pprev);
> >  
> > -/**
> > - * find_vma_intersection() - Look up the first VMA which intersects the interval
> > - * @mm: The process address space.
> > - * @start_addr: The inclusive start user address.
> > - * @end_addr: The exclusive end user address.
> > - *
> > - * Returns: The first VMA within the provided range, %NULL otherwise.  Assumes
> > - * start_addr < end_addr.
> > +/*
> > + * Look up the first VMA which intersects the interval [start_addr, end_addr)
> > + * NULL if none.  Assume start_addr < end_addr.
> >   */
> > -static inline
> > -struct vm_area_struct *find_vma_intersection(struct mm_struct *mm,
> > -					     unsigned long start_addr,
> > -					     unsigned long end_addr)
> > -{
> > -	struct vm_area_struct *vma = find_vma(mm, start_addr);
> > -
> > -	if (vma && end_addr <= vma->vm_start)
> > -		vma = NULL;
> > -	return vma;
> > -}
> > +extern struct vm_area_struct *find_vma_intersection(struct mm_struct *mm,
> > +						    unsigned long start_addr,
> > +						    unsigned long end_addr);
> >  
> >  /**
> >   * vma_lookup() - Find a VMA at a specific address
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index e4c8ce377f2c..c06c5b850e1e 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -2003,29 +2003,47 @@ get_unmapped_area(struct file *file, unsigned long addr, unsigned long len,
> >  EXPORT_SYMBOL(get_unmapped_area);
> >  
> >  /**
> > - * find_vma() - Find the VMA for a given address, or the next vma.
> > - * @mm: The mm_struct to check
> > - * @addr: The address
> > + * find_vma_intersection() - Look up the first VMA which intersects the interval
> > + * @mm: The process address space.
> > + * @start_addr: The inclusive start user address.
> > + * @end_addr: The exclusive end user address.
> >   *
> > - * Returns: The VMA associated with addr, or the next vma.
> > - * May return %NULL in the case of no vma at addr or above.
> > + * Returns: The first VMA within the provided range, %NULL otherwise.  Assumes
> > + * start_addr < end_addr.
> >   */
> > -struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
> > +struct vm_area_struct *find_vma_intersection(struct mm_struct *mm,
> > +					     unsigned long start_addr,
> > +					     unsigned long end_addr)
> >  {
> >  	struct vm_area_struct *vma;
> > -	MA_STATE(mas, &mm->mm_mt, addr, addr);
> > +	MA_STATE(mas, &mm->mm_mt, start_addr, start_addr);
> >  
> >  	mmap_assert_locked(mm);
> >  	/* Check the cache first. */
> > -	vma = vmacache_find(mm, addr);
> > +	vma = vmacache_find(mm, start_addr);
> >  	if (likely(vma))
> >  		return vma;
> >  
> > -	vma = mas_find(&mas, -1);
> > +	vma = mas_find(&mas, end_addr - 1);
> >  	if (vma)
> > -		vmacache_update(addr, vma);
> > +		vmacache_update(mas.index, vma);
> >  	return vma;
> >  }
> > +EXPORT_SYMBOL(find_vma_intersection);
> > +
> > +/**
> > + * find_vma() - Find the VMA for a given address, or the next vma.
> > + * @mm:  The mm_struct to check
> > + * @addr: The address
> > + *
> > + * Returns: The VMA associated with addr, or the next vma.
> > + * May return NULL in the case of no vma at addr or above.
> > + */
> > +inline struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
> 
> I think the inline does nothing here (except maybe for LTO builds). Callers
> will do a function call to find_vma() and then probably that causes another
> function call (likely a tail call) to find_vma_intersection().
> You'd have to put this definition of find_vma() to include/linux/mm.h to
> make the callers inline it and just add the 0 parameter before doing a
> function call of find_vma_intersection() - which would make sense.

Thanks, good to know.  Upon re-examining this change, the find_vma() and
find_vma_intersection() function is later reduced to a few lines of
code.  I will change this change to reduce churn.

> 
> > +{
> > +	// Note find_vma_intersection will decrease 0 to underflow to ULONG_MAX
> 
> Nit: this comment syntax using //.

Thanks, I have checked the entire series and fixed all the ones I added
(and most were later removed).

> 
> > +	return find_vma_intersection(mm, addr, 0);
> > +}
> >  EXPORT_SYMBOL(find_vma);
> >  
> >  /**
> 
>