mm: hugetlb: defer freeing pages when gathering surplus pages

When gathering surplus pages, the number of needed pages is recomputed
after reacquiring hugetlb lock to catch changes in resv_huge_pages and
free_huge_pages.  Plus it is recomputed with the number of newly allocated
pages involved.

Thus freeing pages can be deferred a bit to see if the final page request
is satisfied, though pages could be allocated less than needed.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
Reviewed-by: Michal Hocko <mhocko@suse.cz>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 17 insertions, 13 deletions

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index a876871f6be5..afe3e1ff919b 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -852,6 +852,7 @@ static int gather_surplus_pages(struct hstate *h, int delta)
         struct page *page, *tmp;
         int ret, i;
         int needed, allocated;
+        bool alloc_ok = true;
 
         needed = (h->resv_huge_pages + delta) - h->free_huge_pages;
         if (needed <= 0) {
@@ -867,17 +868,13 @@ retry:
         spin_unlock(&hugetlb_lock);
         for (i = 0; i < needed; i++) {
                 page = alloc_buddy_huge_page(h, NUMA_NO_NODE);
-                if (!page)
-                        /*
-                         * We were not able to allocate enough pages to
-                         * satisfy the entire reservation so we free what
-                         * we've allocated so far.
-                         */
-                        goto free;
-
+                if (!page) {
+                        alloc_ok = false;
+                        break;
+                }
                 list_add(&page->lru, &surplus_list);
         }
-        allocated += needed;
+        allocated += i;
 
         /*
          * After retaking hugetlb_lock, we need to recalculate 'needed'
@@ -886,9 +883,16 @@ retry:
         spin_lock(&hugetlb_lock);
         needed = (h->resv_huge_pages + delta) -
                         (h->free_huge_pages + allocated);
-        if (needed > 0)
-                goto retry;
-
+        if (needed > 0) {
+                if (alloc_ok)
+                        goto retry;
+                /*
+                 * We were not able to allocate enough pages to
+                 * satisfy the entire reservation so we free what
+                 * we've allocated so far.
+                 */
+                goto free;
+        }
         /*
          * The surplus_list now contains _at_least_ the number of extra pages
          * needed to accommodate the reservation.  Add the appropriate number
@@ -914,10 +918,10 @@ retry:
                 VM_BUG_ON(page_count(page));
                 enqueue_huge_page(h, page);
         }
+free:
         spin_unlock(&hugetlb_lock);
 
         /* Free unnecessary surplus pages to the buddy allocator */
-free:
         if (!list_empty(&surplus_list)) {
                 list_for_each_entry_safe(page, tmp, &surplus_list, lru) {
                         list_del(&page->lru);