page allocator: explicitly retry hugepage allocations

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.

Mel tested the patchset on an x86_32 laptop.  With the patches, it was easier
to use the proc interface to grow the hugepage pool.  The following is the
output of a script that grows the pool as much as possible running on
2.6.25-rc9.

Allocating hugepages test
-------------------------
Disabling OOM Killer for current test process
Starting page count: 0
Attempt 1: 57 pages Progress made with 57 pages
Attempt 2: 73 pages Progress made with 16 pages
Attempt 3: 74 pages Progress made with 1 pages
Attempt 4: 75 pages Progress made with 1 pages
Attempt 5: 77 pages Progress made with 2 pages

77 pages was the most it allocated but it took 5 attempts from userspace
to get it. With the 3 patches in this series applied,

Allocating hugepages test
-------------------------
Disabling OOM Killer for current test process
Starting page count: 0
Attempt 1: 75 pages Progress made with 75 pages
Attempt 2: 76 pages Progress made with 1 pages
Attempt 3: 79 pages Progress made with 3 pages

And 79 pages was the most it got. Your patches were able to allocate the
bulk of possible pages on the first attempt.

Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Cc: Andy Whitcroft <apw@shadowen.org>
Tested-by: Mel Gorman <mel@csn.ul.ie>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/hugetlb.c

@@ -199,7 +199,8 @@ 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) {
 		if (arch_prepare_hugepage(page)) {
@@ -294,7 +295,8 @@ 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);