Re: [PATCH v2 4/7] mm/mremap: initial refactor of move_vma()

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Mon, Mar 10, 2025 at 03:11:01PM +0100, Vlastimil Babka wrote:
> On 3/6/25 11:34, Lorenzo Stoakes wrote:
> > Update move_vma() to use the threaded VRM object, de-duplicate code and
> > separate into smaller functions to aid readability and debug-ability.
> >
> > This in turn allows further simplification of expand_vma() as we can
> > simply thread VRM through the function.
> >
> > We also take the opportunity to abstract the account charging page count
> > into the VRM in order that we can correctly thread this through the
> > operation.
> >
> > We additionally do the same for tracking mm statistics - exec_vm,
> > stack_vm, data_vm, and locked_vm.
> >
> > As part of this change, we slightly modify when locked pages statistics
> > are counted for in mm_struct statistics.  However this should cause no
> > issues, as there is no chance of underflow, nor will any rlimit failures
> > occur as a result.
> >
> > This is an intermediate step before a further refactoring of move_vma() in
> > order to aid review.
> >
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> > Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
>
> Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
>
> Can't wait what the bots report what I've missed in this one.
>

Thanks :)

To be fair the other one was an extremely weird edge case where a user
'remaps' a region of a VMA of length 0 onto itself expanding the length 0
mapping to the length of the VMA, i.e. a weird way of doing an unmap.

With that caught, and heavy testing of _real world_ usage of this series
done locally, I think we _should_ be ok... obviously bots have been
hammering with no issues other than aforementioned crazy case.