Re: [PATCH 05/11] mm/sparse-vmemmap: set section order for device DAX

[Qi Zheng]

Hi Muchun,

On 8/31/26 3:53 PM, Muchun Song wrote:
> Device DAX can use vmemmap optimization only when a full section is
> populated with a compound-page geometry. Record that geometry in the
> section order before populating the section, so later vmemmap accounting
> and population decisions can use the section state directly.
>
> Clear the section order when the section becomes empty again. Also reject
> partial additions to a section that already has optimized vmemmap mappings,
> because a section cannot safely mix optimized and ordinary vmemmap layouts.

Perhaps we should explain why they cannot be safely mixed.

> Partial additions continue to use ordinary vmemmap population, so they do
> not save vmemmap memory. Such additions are uncommon, and the lost saving
> is negligible.
>
> Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> ---
>   mm/mm_init.c        | 13 ++++---------
>   mm/sparse-vmemmap.c | 16 ++++++++++++----
>   2 files changed, 16 insertions(+), 13 deletions(-)

Also, the issue sashiko reported looks like it was pre-existing, not
introduced by this patch. So:

Acked-by: Qi Zheng <qi.zheng@xxxxxxxxx>

Thanks,
Qi