Re: [PATCH] mm/mremap: populate calculated fields in vrm state correctly

[Lorenzo Stoakes (ARM)]

On Mon, Oct 19, 2026 at 03:28:27PM +0100, Lorenzo Stoakes (ARM) wrote:
> Commit d5c8aec0542e ("mm/mremap: initial refactor of move_vma()")
> introduced the vma_remap_struct helper to pass state sanely through
> mremap() logic.
>
> Part of this state is vrm->delta - equal to the absolute difference between
> vrm->old_len and vrm->new_len (the old and new lengths of the VMA,
> respectively).
>
> This value is used to correctly charge accounted VMAs.
>
> When shrinking a VMA, mremap_to() sets vrm->old_len equal to vrm->new_len
> having performed the shrink of the VMA first, prior to any potential
> move (e.g. MREMAP_FIXED | MREMAP_MAYMOVE specified).
>
> However it does not recalculate vrm->delta, which results in incorrectly
> overcharging the VMA.

Andrew - could you update this to:

>>
However it does not recalculate vrm->delta, which results in incorrectly
overcharging the VMA when both moving and shrinking a VMA.
<<

To make it clear that only when you do this (rather unusual) action do you
encounter the issue.

--
Cheers, Lorenzo