Re: [PATCH v2 23/33] mm/vma: add and use vma_[add/sub]_pgoff()

[Lorenzo Stoakes (ARM)]

On Wed, Jul 15, 2026 at 07:38:38PM +0200, Vlastimil Babka (SUSE) wrote:
> On 7/10/26 22:17, Lorenzo Stoakes wrote:
> > Add helpers for adding or subtracting to a VMA's page offset, exposed
> > internally for VMA users within mm in mm/vma.h.
> >
> > This is to lay the foundations for tracking anonymous page offset for
> > MAP_PRIVATE file-backed mappings, where adding and subtracting from this
> > value must be reflected in both the file and anonymous offsets.
> >
> > These are used on VMA split and downward stack expansion.
> >
> > No functional change intended.
> >
> > Reviewed-by: Pedro Falcato <pfalcato@xxxxxxx>
> > Signed-off-by: Lorenzo Stoakes <ljs@xxxxxxxxxx>
>
> Reviewed-by: Vlastimil Babka (SUSE) <vbabka@xxxxxxxxxx>

Thanks!

>
> Nits:
>
> > ---
> >  mm/nommu.c |  6 ++++--
> >  mm/vma.c   |  6 +++---
> >  mm/vma.h   | 12 ++++++++++++
> >  3 files changed, 19 insertions(+), 5 deletions(-)
> >
> > diff --git a/mm/nommu.c b/mm/nommu.c
> > index c0a0869cd0d6..2a0136f6081d 100644
> > --- a/mm/nommu.c
> > +++ b/mm/nommu.c
> > @@ -41,6 +41,7 @@
> >  #include <asm/tlbflush.h>
> >  #include <asm/mmu_context.h>
> >  #include "internal.h"
> > +#include "vma.h"
> >
> >  unsigned long highest_memmap_pfn;
> >  int heap_stack_gap = 0;
> > @@ -1361,7 +1362,8 @@ static int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
> >  		region->vm_top = region->vm_end = new->vm_end = addr;
> >  	} else {
> >  		region->vm_start = new->vm_start = addr;
> > -		region->vm_pgoff = new->vm_pgoff += npages;
>
> Ah that takes care of the other case of ugliness I noticed earlier, good.

Churn for good ;)

>
> > +		vma_add_pgoff(new, npages);
> > +		region->vm_pgoff = vma_start_pgoff(new);
> >  	}
> >
> >  	vma_iter_config(vmi, new->vm_start, new->vm_end);
> > @@ -1378,7 +1380,7 @@ static int split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
> >  	delete_nommu_region(vma->vm_region);
> >  	if (new_below) {
> >  		vma->vm_region->vm_start = vma->vm_start = addr;
> > -		vma->vm_pgoff += npages;
> > +		vma_add_pgoff(vma, npages);
> >  		vma->vm_region->vm_pgoff = vma_start_pgoff(vma);
> >  	} else {
> >  		vma->vm_region->vm_end = vma->vm_end = addr;
> > diff --git a/mm/vma.c b/mm/vma.c
> > index 7aa0149f076c..bdd99ba56b4d 100644
> > --- a/mm/vma.c
> > +++ b/mm/vma.c
> > @@ -517,7 +517,7 @@ __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
> >  		new->vm_end = addr;
> >  	} else {
> >  		new->vm_start = addr;
> > -		new->vm_pgoff += linear_page_delta(vma, addr);
> > +		vma_add_pgoff(new, linear_page_delta(vma, addr));
> >  	}
> >
> >  	err = -ENOMEM;
> > @@ -556,7 +556,7 @@ __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
> >
> >  	if (new_below) {
> >  		vma->vm_start = addr;
> > -		vma->vm_pgoff += (addr - new->vm_start) >> PAGE_SHIFT;
> > +		vma_add_pgoff(vma, (addr - new->vm_start) >> PAGE_SHIFT);
>
> Hm isn't this also a case for using linear_page_delta(addr, new)?
> (I guess in patch 21/33)
> Would be like the hunk above.

Ah, yeah :) I can always rearrange which commit does what on any respin.

For now, Andrew - could you make a little edit here?

-		vma_add_pgoff(vma, (addr - new->vm_start) >> PAGE_SHIFT);
+		vma_add_pgoff(vma, linear_page_delta(new, addr));

Thanks!

>
> >  	} else {
> >  		vma->vm_end = addr;
> >  	}
> > @@ -3305,7 +3305,7 @@ int expand_downwards(struct vm_area_struct *vma, unsigned long address)
> >  				vm_stat_account(mm, vma->vm_flags, grow);
> >  				anon_rmap_tree_pre_update_vma(vma);
> >  				vma->vm_start = address;
> > -				vma->vm_pgoff -= grow;
> > +				vma_sub_pgoff(vma, grow);
> >  				/* Overwrite old entry in mtree. */
> >  				vma_iter_store_overwrite(&vmi, vma);
> >  				anon_rmap_tree_post_update_vma(vma);
> > diff --git a/mm/vma.h b/mm/vma.h
> > index 2342516ce00e..47fe35e5307e 100644
> > --- a/mm/vma.h
> > +++ b/mm/vma.h
> > @@ -247,6 +247,18 @@ static inline pgoff_t vmg_end_pgoff(const struct vma_merge_struct *vmg)
> >  	return vmg_start_pgoff(vmg) + vmg_pages(vmg);
> >  }
> >
> > +static inline void vma_add_pgoff(struct vm_area_struct *vma, pgoff_t delta)
> > +{
> > +	vma_assert_can_modify(vma);
> > +	vma->vm_pgoff += delta;
> > +}
> > +
> > +static inline void vma_sub_pgoff(struct vm_area_struct *vma, pgoff_t delta)
> > +{
> > +	vma_assert_can_modify(vma);
> > +	vma->vm_pgoff -= delta;
> > +}
> > +
> >  #define VMG_STATE(name, mm_, vmi_, start_, end_, vma_flags_, pgoff_)	\
> >  	struct vma_merge_struct name = {				\
> >  		.mm = mm_,						\
> >
>

Cheers, Lorenzo