Hi Michal,

I like the idea of postponing the zeroing from the allocation to the
init time. To be honest the improvement looks much larger than I would
expect (Btw. this should be a part of the changelog rather than a
outside link).

The improvements are larger, because this time was never measured, as 
Linux does not have early boot time stamps. I added them for x86 and 
SPARC to emasure the performance. I am pushing those changes through 
separate patchsets.

The implementation just looks too large to what I would expect. E.g. do
we really need to add zero argument to the large part of the memblock
API? Wouldn't it be easier to simply export memblock_virt_alloc_internal
(or its tiny wrapper memblock_virt_alloc_core) and move the zeroing
outside to its 2 callers? A completely untested scratched version at the
end of the email.

I am OK, with this change. But, I do not really see a difference between:

memblock_virt_alloc_raw()
and
memblock_virt_alloc_core()

In both cases we use memblock_virt_alloc_internal(), but the only 
difference is that in my case we tell memblock_virt_alloc_internal() to 
zero the pages if needed, and in your case the other two callers are 
zeroing it. I like moving memblock_dbg() inside 
memblock_virt_alloc_internal()

Also it seems that this is not 100% correct either as it only cares
about VMEMMAP while DEFERRED_STRUCT_PAGE_INIT might be enabled also for
SPARSEMEM. This would suggest that we would zero out pages twice,
right?

Thank you, I will check this combination before sending out the next patch.

A similar concern would go to the memory hotplug patch which will
fall back to the slab/page allocator IIRC. On the other hand
__init_single_page is shared with the hotplug code so again we would
initialize 2 times.

Correct, when memory it hotplugged, to gain the benefit of this fix, and 
also not to regress by actually double zeroing "struct pages" we should 
not zero it out. However, I do not really have means to test it.

So I suspect more changes are needed. I will have a closer look tomorrow.

Thank you for reviewing this work. I will wait for your comments before 
sending out updated patches.

Pasha