Re: [PATCH 25/30] mm/vma: update vmg_adjust_set_range() to offset pgoff instead

On Mon, Jun 29, 2026 at 01:23:36PM +0100, Lorenzo Stoakes wrote:

We are calculating the pgoff as an offset, since we have vma_add_pgoff()
and vma_sub_pgoff() available, just offset this value directly and use
__vma_set_range() for vma->vm_[start, end] values.

We take care to update the range before offsetting the page offset, so the
adjusted VMA's vm_start and vm_pgoff are mutually consistent at the point
the page offset helpers operate - this matters once vma_set_pgoff() comes
to assert invariants which relate the two.

Given the prior code just did it in 3 lines of code with no special
dance, there's a presumption here that this is done in a critical
section and no external actor can see the inconsistent state?

(i.e. range is updated but offset is not)

Just think about this from a bisection/debugging standpoint.

Doing so lays the foundation for future work which allows for use of
virtual page offsets for MAP_PRIVATE-file backed mappings.

No functional change intended.

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

Reviewed-by: Gregory Price <gourry@gourry.net>