On 6/8/26 16:31, Matthew Wilcox wrote: > On Mon, Jun 08, 2026 at 04:26:18PM +0200, David Hildenbrand (Arm) wrote: >> If that means that we would handle __GFP_ZERO consistently in the callers of >> alloc_frozen_pages(), that would also do I guess. We'd still have to pass the >> user address down to some degree, through folio interfaces only at least. > > What I don't understand is how the kernel page allocator needs to know > the user address in order to effectively zero it, but the hypervisor is > able to zero the page without knowing the user address. It feels like > somebody has x86-centric thinking where cache colouring doesn't matter.
(not commenting on the icache dache mess we have to drag along) The thing is that with free-page-reporting the memory is already zeroed by the hypervisor as part of discarding that memory previously (e.g., MADV_DONTNEED) and allocating fresh pages on re-access. So it's not a question of "why is the hypervisor zeroing less efficiently", as zeroing is just a side-product of reclaiming that memory in the first place. -- Cheers, David
