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

["Vlastimil Babka (SUSE)" <vbabka@kernel.org>]

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@suse.de>
> Signed-off-by: Lorenzo Stoakes <ljs@kernel.org>

Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

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.

> +		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.

>  	} 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_,						\
>