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Re: [PATCH -mm] mm: Clear to access sub-page last when clearing huge page

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On Mon, 7 Aug 2017, Huang, Ying wrote:

> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -4374,9 +4374,31 @@ void clear_huge_page(struct page *page,
>  	}
>
>  	might_sleep();
> -	for (i = 0; i < pages_per_huge_page; i++) {
> +	VM_BUG_ON(clamp(addr_hint, addr, addr +
> +			(pages_per_huge_page << PAGE_SHIFT)) != addr_hint);
> +	n = (addr_hint - addr) / PAGE_SIZE;
> +	if (2 * n <= pages_per_huge_page) {
> +		base = 0;
> +		l = n;
> +		for (i = pages_per_huge_page - 1; i >= 2 * n; i--) {
> +			cond_resched();
> +			clear_user_highpage(page + i, addr + i * PAGE_SIZE);
> +		}

I really like the idea behind the patch but this is not clearing from last
to first byte of the huge page.

What seems to be happening here is clearing from the last page to the
first page and I would think that within each page the clearing is from
first byte to last byte. Maybe more gains can be had by really clearing
from last to first byte of the huge page instead of this jumping over 4k
addresses?

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[PATCH -mm] mm: Clear to access sub-page last when clearing huge page "Huang, Ying" <ying.huang@intel.com> - 2017-08-07 09:30 +0200
  Re: [PATCH -mm] mm: Clear to access sub-page last when clearing huge  page Jan Kara <jack@suse.cz> - 2017-08-07 12:00 +0200
    Re: [PATCH -mm] mm: Clear to access sub-page last when clearing huge page "Huang\, Ying" <ying.huang@intel.com> - 2017-08-07 12:10 +0200
  Re: [PATCH -mm] mm: Clear to access sub-page last when clearing huge  page "Kirill A. Shutemov" <kirill@shutemov.name> - 2017-08-07 12:20 +0200
    Re: [PATCH -mm] mm: Clear to access sub-page last when clearing huge page "Huang\, Ying" <ying.huang@intel.com> - 2017-08-08 01:00 +0200
      Re: [PATCH -mm] mm: Clear to access sub-page last when clearing huge page "Huang\, Ying" <ying.huang@intel.com> - 2017-08-08 09:50 +0200
  Re: [PATCH -mm] mm: Clear to access sub-page last when clearing huge  page Christopher Lameter <cl@linux.com> - 2017-08-07 20:50 +0200
    Re: [PATCH -mm] mm: Clear to access sub-page last when clearing huge page "Huang\, Ying" <ying.huang@intel.com> - 2017-08-08 01:10 +0200
    Re: [PATCH -mm] mm: Clear to access sub-page last when clearing huge page "Huang\, Ying" <ying.huang@intel.com> - 2017-08-08 08:30 +0200
  Re: [PATCH -mm] mm: Clear to access sub-page last when clearing huge  page Mike Kravetz <mike.kravetz@oracle.com> - 2017-08-08 06:10 +0200
    Re: [PATCH -mm] mm: Clear to access sub-page last when clearing huge page "Huang\, Ying" <ying.huang@intel.com> - 2017-08-08 06:30 +0200
  Re: [PATCH -mm] mm: Clear to access sub-page last when clearing huge  page Matthew Wilcox <willy@infradead.org> - 2017-08-08 14:20 +0200
    Re: [PATCH -mm] mm: Clear to access sub-page last when clearing huge page "Huang\, Ying" <ying.huang@intel.com> - 2017-08-09 01:10 +0200
  Re: [PATCH -mm] mm: Clear to access sub-page last when clearing  huge page Andrew Morton <akpm@linux-foundation.org> - 2017-08-09 23:30 +0200
    Re: [PATCH -mm] mm: Clear to access sub-page last when clearing huge page "Huang\, Ying" <ying.huang@intel.com> - 2017-08-10 03:00 +0200

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