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
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