Re: [PATCHv5] mm/gup: speed up check_and_migrate_cma_pages() on huge page

[Andrew Morton]

On Thu, 27 Jun 2019 13:15:45 +0800 Pingfan Liu <kernelfans@xxxxxxxxx> wrote:

> Both hugetlb and thp locate on the same migration type of pageblock, since
> they are allocated from a free_list[]. Based on this fact, it is enough to
> check on a single subpage to decide the migration type of the whole huge
> page. By this way, it saves (2M/4K - 1) times loop for pmd_huge on x86,
> similar on other archs.
> 
> Furthermore, when executing isolate_huge_page(), it avoid taking global
> hugetlb_lock many times, and meanless remove/add to the local link list
> cma_page_list.
>

Thanks, looks good to me.  Have any timing measurements been taken?
 
> ...
>
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -1336,25 +1336,30 @@ static long check_and_migrate_cma_pages(struct task_struct *tsk,
>  					struct vm_area_struct **vmas,
>  					unsigned int gup_flags)
>  {
> -	long i;
> +	long i, step;

I'll make these variables unsigned long - to match nr_pages and because
we have no need for them to be negative.

> ...