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

[Ira Weiny]

On Thu, Jun 27, 2019 at 01:15:45PM +0800, Pingfan Liu 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.
> 
> Signed-off-by: Pingfan Liu <kernelfans@xxxxxxxxx>

Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx>

> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> Cc: "Aneesh Kumar K.V" <aneesh.kumar@xxxxxxxxxxxxx>
> Cc: Christoph Hellwig <hch@xxxxxx>
> Cc: Keith Busch <keith.busch@xxxxxxxxx>
> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
> Cc: Linux-kernel@xxxxxxxxxxxxxxx
> ---
> v3 -> v4: fix C language precedence issue
> v4 -> v5: drop the check PageCompound() and improve notes
>  mm/gup.c | 23 +++++++++++++++--------
>  1 file changed, 15 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index ddde097..1deaad2 100644
> --- 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;
>  	bool drain_allow = true;
>  	bool migrate_allow = true;
>  	LIST_HEAD(cma_page_list);
>  
>  check_again:
> -	for (i = 0; i < nr_pages; i++) {
> +	for (i = 0; i < nr_pages;) {
> +
> +		struct page *head = compound_head(pages[i]);
> +
> +		/*
> +		 * gup may start from a tail page. Advance step by the left
> +		 * part.
> +		 */
> +		step = (1 << compound_order(head)) - (pages[i] - head);
>  		/*
>  		 * If we get a page from the CMA zone, since we are going to
>  		 * be pinning these entries, we might as well move them out
>  		 * of the CMA zone if possible.
>  		 */
> -		if (is_migrate_cma_page(pages[i])) {
> -
> -			struct page *head = compound_head(pages[i]);
> -
> -			if (PageHuge(head)) {
> +		if (is_migrate_cma_page(head)) {
> +			if (PageHuge(head))
>  				isolate_huge_page(head, &cma_page_list);
> -			} else {
> +			else {
>  				if (!PageLRU(head) && drain_allow) {
>  					lru_add_drain_all();
>  					drain_allow = false;
> @@ -1369,6 +1374,8 @@ static long check_and_migrate_cma_pages(struct task_struct *tsk,
>  				}
>  			}
>  		}
> +
> +		i += step;
>  	}
>  
>  	if (!list_empty(&cma_page_list)) {
> -- 
> 2.7.5
>