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

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

[Pingfan Liu]

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@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Keith Busch <keith.busch@intel.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Linux-kernel@vger.kernel.org
---
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

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@gmail.com> 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.

> ...

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@gmail.com>

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

> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Ira Weiny <ira.weiny@intel.com>
> Cc: Mike Rapoport <rppt@linux.ibm.com>
> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: John Hubbard <jhubbard@nvidia.com>
> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
> Cc: Christoph Hellwig <hch@lst.de>
> Cc: Keith Busch <keith.busch@intel.com>
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> Cc: Linux-kernel@vger.kernel.org
> ---
> 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
> 

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

[Pingfan Liu]

On Fri, Jun 28, 2019 at 7:25 AM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Thu, 27 Jun 2019 13:15:45 +0800 Pingfan Liu <kernelfans@gmail.com> 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?
Not yet. It is a little hard to force huge page to be allocated CMA
area. Should I provide the measurements?
>
> > ...
> >
> > --- 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.
OK, will fix it.

Thanks,
  Pingfan
>
> > ...