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Re: [v3 0/9] parallelized "struct page" zeroing

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On Tue 09-05-17 14:54:50, Pasha Tatashin wrote:
[...]
> >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()

Well, I didn't object to this particular part. I was mostly concerned
about
http://lkml.kernel.org/r/1494003796-748672-4-git-send-email-pasha.tatashin@oracle.com
and the "zero" argument for other functions. I guess we can do without
that. I _think_ that we should simply _always_ initialize the page at the
__init_single_page time rather than during the allocation. That would
require dropping __GFP_ZERO for non-memblock allocations. Or do you
think we could regress for single threaded initialization?

> >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.

It should be pretty easy to test with kvm, but I can help with testing
on the real HW as well.

Thanks!
-- 
Michal Hocko
SUSE Labs

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[v3 0/9] parallelized "struct page" zeroing Pavel Tatashin <pasha.tatashin@oracle.com> - 2017-05-05 19:10 +0200
  [v3 8/9] powerpc: teach platforms not to zero struct pages memory Pavel Tatashin <pasha.tatashin@oracle.com> - 2017-05-05 19:10 +0200
  [v3 9/9] s390: teach platforms not to zero struct pages memory Pavel Tatashin <pasha.tatashin@oracle.com> - 2017-05-05 19:10 +0200
    Re: [v3 9/9] s390: teach platforms not to zero struct pages memory Heiko Carstens <heiko.carstens@de.ibm.com> - 2017-05-08 13:40 +0200
  [v3 1/9] sparc64: simplify vmemmap_populate Pavel Tatashin <pasha.tatashin@oracle.com> - 2017-05-05 19:10 +0200
  Re: [v3 0/9] parallelized "struct page" zeroing Michal Hocko <mhocko@kernel.org> - 2017-05-09 20:20 +0200
    Re: [v3 0/9] parallelized "struct page" zeroing Pasha Tatashin <pasha.tatashin@oracle.com> - 2017-05-09 21:00 +0200
      Re: [v3 0/9] parallelized "struct page" zeroing Michal Hocko <mhocko@kernel.org> - 2017-05-10 09:30 +0200
        Re: [v3 0/9] parallelized "struct page" zeroing Pasha Tatashin <pasha.tatashin@oracle.com> - 2017-05-10 15:50 +0200
          Re: [v3 0/9] parallelized "struct page" zeroing Michal Hocko <mhocko@kernel.org> - 2017-05-10 17:00 +0200
            Re: [v3 0/9] parallelized "struct page" zeroing Pasha Tatashin <pasha.tatashin@oracle.com> - 2017-05-10 17:10 +0200
              Re: [v3 0/9] parallelized "struct page" zeroing David Miller <davem@davemloft.net> - 2017-05-10 17:30 +0200
            Re: [v3 0/9] parallelized "struct page" zeroing David Miller <davem@davemloft.net> - 2017-05-10 17:20 +0200
              Re: [v3 0/9] parallelized "struct page" zeroing Matthew Wilcox <willy@infradead.org> - 2017-05-10 19:20 +0200
                Re: [v3 0/9] parallelized "struct page" zeroing David Miller <davem@davemloft.net> - 2017-05-10 20:10 +0200
                Re: [v3 0/9] parallelized "struct page" zeroing Matthew Wilcox <willy@infradead.org> - 2017-05-10 23:20 +0200
              Re: [v3 0/9] parallelized "struct page" zeroing Michal Hocko <mhocko@kernel.org> - 2017-05-11 10:10 +0200
                Re: [v3 0/9] parallelized "struct page" zeroing David Miller <davem@davemloft.net> - 2017-05-11 16:40 +0200

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