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
>
>
