On Tue, Mar 23, 2021 at 09:12:15PM +0800, Liu Shixin wrote:
> From: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
>
> The start_pfn and end_pfn are already available in move_freepages_block(),
> there is no need to go back and forth between page and pfn in move_freepages
> and move_freepages_block, and pfn_valid_within() should validate pfn first
> before touching the page.
This looks good to me:
Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
> static int move_freepages(struct zone *zone,
> - struct page *start_page, struct page *end_page,
> + unsigned long start_pfn, unsigned long end_pfn,
> int migratetype, int *num_movable)
> {
> struct page *page;
> + unsigned long pfn;
> unsigned int order;
> int pages_moved = 0;
>
> - for (page = start_page; page <= end_page;) {
> - if (!pfn_valid_within(page_to_pfn(page))) {
> - page++;
> + for (pfn = start_pfn; pfn <= end_pfn;) {
> + if (!pfn_valid_within(pfn)) {
> + pfn++;
> continue;
> }
>
> + page = pfn_to_page(pfn);
I wonder if this wouldn't be even better if we did:
struct page *start_page = pfn_to_page(start_pfn);
for (pfn = start_pfn; pfn <= end_pfn; pfn++) {
struct page *page = start_page + pfn - start_pfn;
if (!pfn_valid_within(pfn))
continue;
> -
> - page++;
> + pfn++;
> continue;
... then we can drop the increment of pfn here
> }
>
> @@ -2458,7 +2459,7 @@ static int move_freepages(struct zone *zone,
>
> order = buddy_order(page);
> move_to_free_list(page, zone, order, migratetype);
> - page += 1 << order;
> + pfn += 1 << order;
... and change this to pfn += (1 << order) - 1;
Do you have any numbers to quantify the benefit of this change?
