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

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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@xxxxxxxxxx
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?


Hi Michal,

Thats exactly right, I am worried that we will regress when there is no parallelized initialization of "struct pages" if we force unconditionally do memset() in __init_single_page(). The overhead of calling memset() on a smaller chunks (64-bytes) may cause the regression, this is why I opted only for parallelized case to zero this metadata. This way, we are guaranteed to see great improvements from this change without having regressions on platforms and builds that do not support parallelized initialization of "struct pages".

However, on some chips such as latest SPARCs it is beneficial to have memset() right inside __init_single_page() even for single threaded case, because it can act as a prefetch on chips with optimized block initialized store instructions.

Pasha
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