On Wed, Jul 15, 2026 at 05:23:09PM +0200, Vlastimil Babka (SUSE) wrote:
> On 7/10/26 22:16, Lorenzo Stoakes wrote:
> > There are many instances in which linear_page_index() (as well as
> > linear_page_delta()) is open-coded, which is confusing and inconsistent.
> >
> > Additionally, vma->vm_pgoff doesn't necessarily make it clear that this is
> > the page offset of the start of the VMA range.
> >
> > Doing so also aids greppability.
> >
> > So use vma_start_pgoff() in favour of directly accessing vma->vm_pgoff, and
> > linear_page_index() where we can.
> >
> > This also lays the ground for future changes which will add an anonymous
> > page offset in order to be able to index MAP_PRIVATE-file backed anon
> > folios in terms of their virtual page offset.
> >
> > No functional change intended.
> >
> > Reviewed-by: Gregory Price <[email protected]>
> > Reviewed-by: SJ Park <[email protected]>
> > Reviewed-by: Pedro Falcato <[email protected]>
> > Signed-off-by: Lorenzo Stoakes <[email protected]>
>
> Reviewed-by: Vlastimil Babka (SUSE) <[email protected]>
Thanks!
>
> Nit:
>
> > diff --git a/mm/damon/vaddr.c b/mm/damon/vaddr.c
> > index 2058db9c01d5..d10b8042adb5 100644
> > --- a/mm/damon/vaddr.c
> > +++ b/mm/damon/vaddr.c
> > @@ -10,6 +10,7 @@
> > #include <linux/mman.h>
> > #include <linux/mmu_notifier.h>
> > #include <linux/page_idle.h>
> > +#include <linux/pagemap.h>
> > #include <linux/pagewalk.h>
> > #include <linux/sched/mm.h>
> >
> > @@ -623,8 +624,8 @@ static void damos_va_migrate_dests_add(struct folio
> > *folio,
> > }
> >
> > order = folio_order(folio);
> > - ilx = vma->vm_pgoff >> order;
> > - ilx += (addr - vma->vm_start) >> (PAGE_SHIFT + order);
> > + ilx = vma_start_pgoff(vma) >> order;
> > + ilx += linear_page_delta(vma, addr) >> order;
>
> Could these be combined to linear_page_index(vma, addr) >> order?
So this is:
(x >> order) + (y >> order)
And linear_page_index(vma, addr) >> order is:
(x + y) >> order
Consider:
order = 1, x = 0b11, y = 0b01
(x >> order) + (y >> order) =
(0b11 >> 1 ) + (0b01 >> 1 ) =
0b1 + 0 =
1
(x + y ) >> order =
(0b11 + 0b01) >> 1 =
(0b100 ) >> 1 =
2
They are not equivalent - the carry bit changes the result.
>
> >
> > for (i = 0; i < dests->nr_dests; i++)
> > weight_total += dests->weight_arr[i];
>
> > diff --git a/mm/filemap.c b/mm/filemap.c
> > index b39111abdc4b..1dbb4c6f824e 100644
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -3411,8 +3411,8 @@ static struct file *do_sync_mmap_readahead(struct
> > vm_fault *vmf)
> > * of memory.
> > */
> > struct vm_area_struct *vma = vmf->vma;
> > - unsigned long start = vma->vm_pgoff;
> > - unsigned long end = start + vma_pages(vma);
> > + const unsigned long start = vma_start_pgoff(vma);
> > + const unsigned long end = vma_end_pgoff(vma);
> > unsigned long ra_end;
> >
> > ra->order = exec_folio_order();
> > @@ -3930,7 +3930,8 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf,
> > goto out;
> > }
> >
> > - addr = vma->vm_start + ((start_pgoff - vma->vm_pgoff) << PAGE_SHIFT);
> > + addr = vma->vm_start +
> > + ((start_pgoff - vma_start_pgoff(vma)) << PAGE_SHIFT);
>
> This could be linear_page_index(vma, start_pgoff) <<
>
> > vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, addr, &vmf->ptl);
> > if (!vmf->pte) {
> > folio_unlock(folio);
>
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -2049,8 +2049,8 @@ struct mempolicy *get_vma_policy(struct
> > vm_area_struct *vma,
> > pol = get_task_policy(current);
> > if (pol->mode == MPOL_INTERLEAVE ||
> > pol->mode == MPOL_WEIGHTED_INTERLEAVE) {
> > - *ilx += vma->vm_pgoff >> order;
> > - *ilx += (addr - vma->vm_start) >> (PAGE_SHIFT + order);
> > + *ilx += vma_start_pgoff(vma) >> order;
> > + *ilx += linear_page_delta(vma, addr) >> order;
>
> Also?
See above.
>
> > }
> > return pol;
> > }
>
> > --- a/mm/nommu.c
> > +++ b/mm/nommu.c
> > @@ -975,7 +975,7 @@ static int do_mmap_private(struct vm_area_struct *vma,
> > /* read the contents of a file into the copy */
> > loff_t fpos;
> >
> > - fpos = vma->vm_pgoff;
> > + fpos = vma_start_pgoff(vma);
> > fpos <<= PAGE_SHIFT;
> >
> > ret = kernel_read(vma->vm_file, base, len, &fpos);
> > @@ -1378,7 +1378,8 @@ 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_region->vm_pgoff = vma->vm_pgoff += npages;
>
> yuck, good to remove that ugly construct
> it's not the only occurence in this function
> oh well
Yup at least improved it here :)
>
> > + vma->vm_pgoff += npages;
> > + vma->vm_region->vm_pgoff = vma_start_pgoff(vma);
> > } else {
> > vma->vm_region->vm_end = vma->vm_end = addr;
> > vma->vm_region->vm_top = addr;
Cheers, Lorenzo
