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-rw-r--r--mm/hugetlb.c37
1 files changed, 28 insertions, 9 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 3edb759c5c7d..c7025c132670 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1773,23 +1773,32 @@ free:
}
/*
- * When releasing a hugetlb pool reservation, any surplus pages that were
- * allocated to satisfy the reservation must be explicitly freed if they were
- * never used.
- * Called with hugetlb_lock held.
+ * This routine has two main purposes:
+ * 1) Decrement the reservation count (resv_huge_pages) by the value passed
+ * in unused_resv_pages. This corresponds to the prior adjustments made
+ * to the associated reservation map.
+ * 2) Free any unused surplus pages that may have been allocated to satisfy
+ * the reservation. As many as unused_resv_pages may be freed.
+ *
+ * Called with hugetlb_lock held. However, the lock could be dropped (and
+ * reacquired) during calls to cond_resched_lock. Whenever dropping the lock,
+ * we must make sure nobody else can claim pages we are in the process of
+ * freeing. Do this by ensuring resv_huge_page always is greater than the
+ * number of huge pages we plan to free when dropping the lock.
*/
static void return_unused_surplus_pages(struct hstate *h,
unsigned long unused_resv_pages)
{
unsigned long nr_pages;
- /* Uncommit the reservation */
- h->resv_huge_pages -= unused_resv_pages;
-
/* Cannot return gigantic pages currently */
if (hstate_is_gigantic(h))
- return;
+ goto out;
+ /*
+ * Part (or even all) of the reservation could have been backed
+ * by pre-allocated pages. Only free surplus pages.
+ */
nr_pages = min(unused_resv_pages, h->surplus_huge_pages);
/*
@@ -1799,12 +1808,22 @@ static void return_unused_surplus_pages(struct hstate *h,
* when the nodes with surplus pages have no free pages.
* free_pool_huge_page() will balance the the freed pages across the
* on-line nodes with memory and will handle the hstate accounting.
+ *
+ * Note that we decrement resv_huge_pages as we free the pages. If
+ * we drop the lock, resv_huge_pages will still be sufficiently large
+ * to cover subsequent pages we may free.
*/
while (nr_pages--) {
+ h->resv_huge_pages--;
+ unused_resv_pages--;
if (!free_pool_huge_page(h, &node_states[N_MEMORY], 1))
- break;
+ goto out;
cond_resched_lock(&hugetlb_lock);
}
+
+out:
+ /* Fully uncommit the reservation */
+ h->resv_huge_pages -= unused_resv_pages;
}