hugetlb: balance freeing of huge pages across nodes

Free huges pages from nodes in round robin fashion in an attempt to keep
[persistent a.k.a static] hugepages balanced across nodes

New function free_pool_huge_page() is modeled on and performs roughly the
inverse of alloc_fresh_huge_page().  Replaces dequeue_huge_page() which
now has no callers, so this patch removes it.

Helper function hstate_next_node_to_free() uses new hstate member
next_to_free_nid to distribute "frees" across all nodes with huge pages.

Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Acked-by: Mel Gorman <mel@csn.ul.ie>
Cc: Nishanth Aravamudan <nacc@us.ibm.com>
Cc: Adam Litke <agl@us.ibm.com>
Cc: Andy Whitcroft <apw@canonical.com>
Cc: Eric Whitney <eric.whitney@hp.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 86 insertions, 46 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index b16d63634777..38dab5586827 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -456,24 +456,6 @@ static void enqueue_huge_page(struct hstate *h, struct page *page)
         h->free_huge_pages_node[nid]++;
 }
 
-static struct page *dequeue_huge_page(struct hstate *h)
-{
-        int nid;
-        struct page *page = NULL;
-
-        for (nid = 0; nid < MAX_NUMNODES; ++nid) {
-                if (!list_empty(&h->hugepage_freelists[nid])) {
-                        page = list_entry(h->hugepage_freelists[nid].next,
-                                          struct page, lru);
-                        list_del(&page->lru);
-                        h->free_huge_pages--;
-                        h->free_huge_pages_node[nid]--;
-                        break;
-                }
-        }
-        return page;
-}
-
 static struct page *dequeue_huge_page_vma(struct hstate *h,
                                 struct vm_area_struct *vma,
                                 unsigned long address, int avoid_reserve)
@@ -641,7 +623,7 @@ static struct page *alloc_fresh_huge_page_node(struct hstate *h, int nid)
 
 /*
  * Use a helper variable to find the next node and then
- * copy it back to hugetlb_next_nid afterwards:
+ * copy it back to next_nid_to_alloc afterwards:
  * otherwise there's a window in which a racer might
  * pass invalid nid MAX_NUMNODES to alloc_pages_exact_node.
  * But we don't need to use a spin_lock here: it really
@@ -650,13 +632,13 @@ static struct page *alloc_fresh_huge_page_node(struct hstate *h, int nid)
  * if we just successfully allocated a hugepage so that
  * the next caller gets hugepages on the next node.
  */
-static int hstate_next_node(struct hstate *h)
+static int hstate_next_node_to_alloc(struct hstate *h)
 {
         int next_nid;
-        next_nid = next_node(h->hugetlb_next_nid, node_online_map);
+        next_nid = next_node(h->next_nid_to_alloc, node_online_map);
         if (next_nid == MAX_NUMNODES)
                 next_nid = first_node(node_online_map);
-        h->hugetlb_next_nid = next_nid;
+        h->next_nid_to_alloc = next_nid;
         return next_nid;
 }
 
@@ -667,14 +649,15 @@ static int alloc_fresh_huge_page(struct hstate *h)
         int next_nid;
         int ret = 0;
 
-        start_nid = h->hugetlb_next_nid;
+        start_nid = h->next_nid_to_alloc;
+        next_nid = start_nid;
 
         do {
-                page = alloc_fresh_huge_page_node(h, h->hugetlb_next_nid);
+                page = alloc_fresh_huge_page_node(h, next_nid);
                 if (page)
                         ret = 1;
-                next_nid = hstate_next_node(h);
-        } while (!page && h->hugetlb_next_nid != start_nid);
+                next_nid = hstate_next_node_to_alloc(h);
+        } while (!page && next_nid != start_nid);
 
         if (ret)
                 count_vm_event(HTLB_BUDDY_PGALLOC);
@@ -684,6 +667,52 @@ static int alloc_fresh_huge_page(struct hstate *h)
         return ret;
 }
 
+/*
+ * helper for free_pool_huge_page() - find next node
+ * from which to free a huge page
+ */
+static int hstate_next_node_to_free(struct hstate *h)
+{
+        int next_nid;
+        next_nid = next_node(h->next_nid_to_free, node_online_map);
+        if (next_nid == MAX_NUMNODES)
+                next_nid = first_node(node_online_map);
+        h->next_nid_to_free = next_nid;
+        return next_nid;
+}
+
+/*
+ * Free huge page from pool from next node to free.
+ * Attempt to keep persistent huge pages more or less
+ * balanced over allowed nodes.
+ * Called with hugetlb_lock locked.
+ */
+static int free_pool_huge_page(struct hstate *h)
+{
+        int start_nid;
+        int next_nid;
+        int ret = 0;
+
+        start_nid = h->next_nid_to_free;
+        next_nid = start_nid;
+
+        do {
+                if (!list_empty(&h->hugepage_freelists[next_nid])) {
+                        struct page *page =
+                                list_entry(h->hugepage_freelists[next_nid].next,
+                                          struct page, lru);
+                        list_del(&page->lru);
+                        h->free_huge_pages--;
+                        h->free_huge_pages_node[next_nid]--;
+                        update_and_free_page(h, page);
+                        ret = 1;
+                }
+                next_nid = hstate_next_node_to_free(h);
+        } while (!ret && next_nid != start_nid);
+
+        return ret;
+}
+
 static struct page *alloc_buddy_huge_page(struct hstate *h,
                         struct vm_area_struct *vma, unsigned long address)
 {
@@ -1008,7 +1037,7 @@ int __weak alloc_bootmem_huge_page(struct hstate *h)
                 void *addr;
 
                 addr = __alloc_bootmem_node_nopanic(
-                                NODE_DATA(h->hugetlb_next_nid),
+                                NODE_DATA(h->next_nid_to_alloc),
                                 huge_page_size(h), huge_page_size(h), 0);
 
                 if (addr) {
@@ -1020,7 +1049,7 @@ int __weak alloc_bootmem_huge_page(struct hstate *h)
                         m = addr;
                         goto found;
                 }
-                hstate_next_node(h);
+                hstate_next_node_to_alloc(h);
                 nr_nodes--;
         }
         return 0;
@@ -1141,31 +1170,43 @@ static inline void try_to_free_low(struct hstate *h, unsigned long count)
  */
 static int adjust_pool_surplus(struct hstate *h, int delta)
 {
-        static int prev_nid;
-        int nid = prev_nid;
+        int start_nid, next_nid;
         int ret = 0;
 
         VM_BUG_ON(delta != -1 && delta != 1);
-        do {
-                nid = next_node(nid, node_online_map);
-                if (nid == MAX_NUMNODES)
-                        nid = first_node(node_online_map);
 
-                /* To shrink on this node, there must be a surplus page */
-                if (delta < 0 && !h->surplus_huge_pages_node[nid])
-                        continue;
-                /* Surplus cannot exceed the total number of pages */
-                if (delta > 0 && h->surplus_huge_pages_node[nid] >=
+        if (delta < 0)
+                start_nid = h->next_nid_to_alloc;
+        else
+                start_nid = h->next_nid_to_free;
+        next_nid = start_nid;
+
+        do {
+                int nid = next_nid;
+                if (delta < 0)  {
+                        next_nid = hstate_next_node_to_alloc(h);
+                        /*
+                         * To shrink on this node, there must be a surplus page
+                         */
+                        if (!h->surplus_huge_pages_node[nid])
+                                continue;
+                }
+                if (delta > 0) {
+                        next_nid = hstate_next_node_to_free(h);
+                        /*
+                         * Surplus cannot exceed the total number of pages
+                         */
+                        if (h->surplus_huge_pages_node[nid] >=
                                                 h->nr_huge_pages_node[nid])
-                        continue;
+                                continue;
+                }
 
                 h->surplus_huge_pages += delta;
                 h->surplus_huge_pages_node[nid] += delta;
                 ret = 1;
                 break;
-        } while (nid != prev_nid);
+        } while (next_nid != start_nid);
 
-        prev_nid = nid;
         return ret;
 }
 
@@ -1227,10 +1268,8 @@ static unsigned long set_max_huge_pages(struct hstate *h, unsigned long count)
         min_count = max(count, min_count);
         try_to_free_low(h, min_count);
         while (min_count < persistent_huge_pages(h)) {
-                struct page *page = dequeue_huge_page(h);
-                if (!page)
+                if (!free_pool_huge_page(h))
                         break;
-                update_and_free_page(h, page);
         }
         while (count < persistent_huge_pages(h)) {
                 if (!adjust_pool_surplus(h, 1))
@@ -1442,7 +1481,8 @@ void __init hugetlb_add_hstate(unsigned order)
         h->free_huge_pages = 0;
         for (i = 0; i < MAX_NUMNODES; ++i)
                 INIT_LIST_HEAD(&h->hugepage_freelists[i]);
-        h->hugetlb_next_nid = first_node(node_online_map);
+        h->next_nid_to_alloc = first_node(node_online_map);
+        h->next_nid_to_free = first_node(node_online_map);
         snprintf(h->name, HSTATE_NAME_LEN, "hugepages-%lukB",
                                         huge_page_size(h)/1024);