Re: [PATCH] mm: skip invalid pages block at a time in zero_resv_unresv

[Naoya Horiguchi]

On Fri, Jun 15, 2018 at 11:57:33AM -0400, Pavel Tatashin wrote:
> The role of zero_resv_unavail() is to make sure that every struct page that
> is allocated but is not backed by memory that is accessible by kernel is
> zeroed and not in some uninitialized state.
> 
> Since struct pages are allocated in blocks (2M pages in x86 case), we can
> skip pageblock_nr_pages at a time, when the first one is found to be
> invalid.
> 
> This optimization may help since now on x86 every hole in e820 maps
> is marked as reserved in memblock, and thus will go through this function.
> 
> This function is called before sched_clock() is initialized, so I used my
> x86 early boot clock patches to measure the performance improvement.
> 
> With 1T hole on i7-8700 currently we would take 0.606918s of boot time, but
> with this optimization 0.001103s.
> 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>

Looks good to me, thanks!

Reviewed-by: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>

> ---
>  mm/page_alloc.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 1521100f1e63..94f1b3201735 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -6404,8 +6404,11 @@ void __paginginit zero_resv_unavail(void)
>  	pgcnt = 0;
>  	for_each_resv_unavail_range(i, &start, &end) {
>  		for (pfn = PFN_DOWN(start); pfn < PFN_UP(end); pfn++) {
> -			if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages)))
> +			if (!pfn_valid(ALIGN_DOWN(pfn, pageblock_nr_pages))) {
> +				pfn = ALIGN_DOWN(pfn, pageblock_nr_pages)
> +					+ pageblock_nr_pages - 1;
>  				continue;
> +			}
>  			mm_zero_struct_page(pfn_to_page(pfn));
>  			pgcnt++;
>  		}
> -- 
> 2.17.1
> 
>