> On Sep 5, 2026, at 16:20, Qi Zheng <[email protected]> wrote:
>
> Hi Muchun,
Hi,
>
> 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.
Yes, because compound_nr_pages() determines the number of struct pages to
initialize with section as the smallest granularity, they cannot be 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 <[email protected]>
>> ---
>> 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 <[email protected]>
Thanks.
>
> Thanks,
> Qi
>
