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Subject[PATCHv3] mm/gup: speed up check_and_migrate_cma_pages() on huge page
Date
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
---
v2 -> v3: fix page order to size convertion

mm/gup.c | 19 ++++++++++++-------
1 file changed, 12 insertions(+), 7 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index ddde097..03cc1f4 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1342,19 +1342,22 @@ static long check_and_migrate_cma_pages(struct task_struct *tsk,
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]);
+ long step = 1;
+
+ if (PageCompound(head))
+ 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 +1372,8 @@ static long check_and_migrate_cma_pages(struct task_struct *tsk,
}
}
}
+
+ i += step;
}

if (!list_empty(&cma_page_list)) {
--
2.7.5
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