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

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.

[akpm@linux-foundation.org: make `i' and `step' unsigned]
Link: http://lkml.kernel.org/r/1561612545-28997-1-git-send-email-kernelfans@gmail.com
Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: 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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 8 deletions

diff --git a/mm/gup.c b/mm/gup.c
index 83d480e9b05f..f411bab037f5 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1449,25 +1449,31 @@ static long check_and_migrate_cma_pages(struct task_struct *tsk,
                                         struct vm_area_struct **vmas,
                                         unsigned int gup_flags)
 {
-        long i;
+        unsigned long i;
+        unsigned long 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;
@@ -1482,6 +1488,8 @@ check_again:
                                 }
                         }
                 }
+
+                i += step;
         }
 
         if (!list_empty(&cma_page_list)) {