On Wed, Jul 29, 2020 at 03:03:04PM +0200, David Hildenbrand wrote: > On 29.07.20 15:00, Mike Rapoport wrote: > > On Wed, Jul 29, 2020 at 11:35:20AM +0200, David Hildenbrand wrote: > >>> > >>> There is still large gap with ARM64_64K_PAGES, though. > >>> > >>> As for SPARSEMEM without VMEMMAP, are there actual benefits to use it? > >> > >> I was asking myself the same question a while ago and didn't really find > >> a compelling one. > > > > Memory overhead for VMEMMAP is larger, especially for arm64 that knows > > how to free empty parts of the memory map with "classic" SPARSEMEM. > > You mean the hole punching within section memmap? (which is why their > pfn_valid() implementation is special) Yes, arm (both 32 and 64) do this. And for smaller systems with a few memory banks this is very reasonable to trade slight (if any) slowdown in pfn_valid() for several megs of memory. > (I do wonder why that shouldn't work with VMEMMAP, or is it simply not > implemented?) It's not implemented. There was a patch [1] recently to implement this. [1] https://lore.kernel.org/lkml/20200721073203.107862-1-liwei213@xxxxxxxxxx/ > -- > Thanks, > > David / dhildenb > -- Sincerely yours, Mike.
