Re: [PATCH mm-new v7 4/5] mm: khugepaged: skip lazy-free folios
From: David Hildenbrand (Arm)
Date: Sat Feb 07 2026 - 17:25:38 EST
On 2/7/26 23:17, Barry Song wrote:
On Sun, Feb 8, 2026 at 6:05 AM David Hildenbrand (Arm) <david@xxxxxxxxxx> wrote:
On 2/7/26 23:01, Barry Song wrote:
If there is no memory pressure in the system, why wouldn't you just want
Maybe change “just not skip” to “just skip”?
If the goal is to avoid the collapse overhead for folios that are
about to be dropped, we might consider skipping collapse for the
entire VMA？
to collapse in a VM_DROPPABLE region?
"about to be dropped" only applies once there is actual memory pressure.
If not, these pages stick around forever.
agree. But this brings us back to the philosophy of the original patch.
If there is no memory pressure, lazyfree folios won’t be dropped, so
collapsing them might also be reasonable.
It's about memory pressure in the future.
Just collapsing fully lazyfree folios with VM_DROPPABLE while
skipping partially lazyfree VMAs seems a bit confusing to me :-)
Think of it like this:
All folios in VM_DROPPABLE are lazyfree. Collapsing maintains that property. So you can just collapse and memory pressure in the future will free it up.
In contrast, collapsing in !VM_DROPPABLE does not maintain that property. The collapsed folio will not be lazyfree and memory pressure in the future will not be able to free it up.
--
Cheers,
David