[PATCH RFC 1/3] mm/hugetlb: split alloc_fresh_huge_page_node into fast and slow path

[Jia He <hejianet@gmail.com>]

This patch split alloc_fresh_huge_page_node into 2 parts:
- fast path without __GFP_REPEAT flag
- slow path with __GFP_REPEAT flag

Thus, if there is a server with uneven numa memory layout:
available: 7 nodes (0-6)
node 0 cpus: 0 1 2 3 4 5 6 7
node 0 size: 6603 MB
node 0 free: 91 MB
node 1 cpus:
node 1 size: 12527 MB
node 1 free: 157 MB
node 2 cpus:
node 2 size: 15087 MB
node 2 free: 189 MB
node 3 cpus:
node 3 size: 16111 MB
node 3 free: 205 MB
node 4 cpus: 8 9 10 11 12 13 14 15
node 4 size: 24815 MB
node 4 free: 310 MB
node 5 cpus:
node 5 size: 4095 MB
node 5 free: 61 MB
node 6 cpus:
node 6 size: 22750 MB
node 6 free: 283 MB
node distances:
node   0   1   2   3   4   5   6
  0:  10  20  40  40  40  40  40
  1:  20  10  40  40  40  40  40
  2:  40  40  10  20  40  40  40
  3:  40  40  20  10  40  40  40
  4:  40  40  40  40  10  20  40
  5:  40  40  40  40  20  10  40
  6:  40  40  40  40  40  40  10

In this case node 5 has less memory and we will alloc the hugepages
from these nodes one by one.
After this patch, we will not trigger too early direct memory/kswap
reclaim for node 5 if there are enough memory in other nodes.

Signed-off-by: Jia He <hejianet@gmail.com>
---
 mm/hugetlb.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index c7025c1..f2415ce 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1364,10 +1364,19 @@ static struct page *alloc_fresh_huge_page_node(struct hstate *h, int nid)
 {
 	struct page *page;
 
+	/* fast path without __GFP_REPEAT */
 	page = __alloc_pages_node(nid,
 		htlb_alloc_mask(h)|__GFP_COMP|__GFP_THISNODE|
 						__GFP_REPEAT|__GFP_NOWARN,
 		huge_page_order(h));
+
+	/* slow path with __GFP_REPEAT*/
+	if (!page)
+		page = __alloc_pages_node(nid,
+			htlb_alloc_mask(h)|__GFP_COMP|__GFP_THISNODE|
+					__GFP_NOWARN,
+			huge_page_order(h));
+
 	if (page) {
 		prep_new_huge_page(h, page, nid);
 	}
-- 
2.5.5