Re: [v1 0/5] parallelized "struct page" zeroing

[Matthew Wilcox]

On Thu, Mar 23, 2017 at 07:01:48PM -0400, Pavel Tatashin wrote:
> When deferred struct page initialization feature is enabled, we get a
> performance gain of initializing vmemmap in parallel after other CPUs are
> started. However, we still zero the memory for vmemmap using one boot CPU.
> This patch-set fixes the memset-zeroing limitation by deferring it as well.
> 
> Here is example performance gain on SPARC with 32T:
> base
> https://hastebin.com/ozanelatat.go
> 
> fix
> https://hastebin.com/utonawukof.go
> 
> As you can see without the fix it takes: 97.89s to boot
> With the fix it takes: 46.91 to boot.

How long does it take if we just don't zero this memory at all?  We seem
to be initialising most of struct page in __init_single_page(), so it
seems like a lot of additional complexity to conditionally zero the rest
of struct page.