On Wed, Jul 29, 2020 at 03:03:04PM +0200, David Hildenbrand wrote:

On 29.07.20 15:00, Mike Rapoport wrote:

quoted

On Wed, Jul 29, 2020 at 11:35:20AM +0200, David Hildenbrand wrote:

quoted

quoted

 
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@huawei.com/ (local)

-- 
Thanks,

David / dhildenb

-- 
Sincerely yours,
Mike.

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