[RFC][PATCH 2/2] Explicitly retry hugepage allocations

[Nishanth Aravamudan <nacc@us.ibm.com>]

Add __GFP_REPEAT to hugepage allocations. Do so to not necessitate
userspace putting pressure on the VM by repeated echo's into
/proc/sys/vm/nr_hugepages to grow the pool. With the previous patch to
allow for large-order __GFP_REPEAT attempts to loop for a bit (as
opposed to indefinitely), this increases the likelihood of getting
hugepages when the system experiences (or recently experienced) load.

On a 2-way x86_64, this doubles the number of hugepages (from 10 to 20)
obtained while compiling a kernel at the same time. On a 4-way ppc64,
a similar scale increase is seen (from 3 to 5 hugepages). Finally, on a
2-way x86, this leads to a 5-fold increase in the hugepages allocatable
under load (90 to 554).

Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 1a56420..0358a91 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -176,7 +176,8 @@ static struct page *alloc_fresh_huge_page_node(int nid)
 	struct page *page;
 
 	page = alloc_pages_node(nid,
-		htlb_alloc_mask|__GFP_COMP|__GFP_THISNODE|__GFP_NOWARN,
+		htlb_alloc_mask|__GFP_COMP|__GFP_THISNODE|
+						__GFP_REPEAT|__GFP_NOWARN,
 		HUGETLB_PAGE_ORDER);
 	if (page) {
 		set_compound_page_dtor(page, free_huge_page);
@@ -262,7 +263,8 @@ static struct page *alloc_buddy_huge_page(struct vm_area_struct *vma,
 	}
 	spin_unlock(&hugetlb_lock);
 
-	page = alloc_pages(htlb_alloc_mask|__GFP_COMP|__GFP_NOWARN,
+	page = alloc_pages(htlb_alloc_mask|__GFP_COMP|
+					__GFP_REPEAT|__GFP_NOWARN,
 					HUGETLB_PAGE_ORDER);
 
 	spin_lock(&hugetlb_lock);

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