diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 24968790bc3e3c451f178a1605e9eecb01acf918..f7bc869a29b8c7414c845be95987c4a1b403eb9f 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -34,6 +34,7 @@ void hugetlb_unreserve_pages(struct inode *inode, long offset, long freed);
extern unsigned long max_huge_pages;
extern unsigned long hugepages_treat_as_movable;
extern int hugetlb_dynamic_pool;
+extern unsigned long nr_overcommit_huge_pages;
extern const unsigned long hugetlb_zero, hugetlb_infinity;
extern int sysctl_hugetlb_shm_group;
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 8ac51714b08ca7ec4261b8544fc62524dad8a3e4..b85a1282605dabd592f4b29a24ed81d157444500 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -912,6 +912,14 @@ static struct ctl_table vm_table[] = {
.mode = 0644,
.proc_handler = &proc_dointvec,
},
+ {
+ .ctl_name = CTL_UNNUMBERED,
+ .procname = "nr_overcommit_hugepages",
+ .data = &nr_overcommit_huge_pages,
+ .maxlen = sizeof(nr_overcommit_huge_pages),
+ .mode = 0644,
+ .proc_handler = &proc_doulongvec_minmax,
+ },
#endif
{
.ctl_name = VM_LOWMEM_RESERVE_RATIO,
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 6f978218c2c808b7dad3e0c184cc44ec35f2585d..3a790651475a067c7cb8798f669fecd8796835c6 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -32,6 +32,7 @@ static unsigned int surplus_huge_pages_node[MAX_NUMNODES];
static gfp_t htlb_alloc_mask = GFP_HIGHUSER;
unsigned long hugepages_treat_as_movable;
int hugetlb_dynamic_pool;
+unsigned long nr_overcommit_huge_pages;
static int hugetlb_next_nid;
/*
@@ -227,22 +228,62 @@ static struct page *alloc_buddy_huge_page(struct vm_area_struct *vma,
unsigned long address)
{
struct page *page;
+ unsigned int nid;
/* Check if the dynamic pool is enabled */
if (!hugetlb_dynamic_pool)
return NULL;
+ /*
+ * Assume we will successfully allocate the surplus page to
+ * prevent racing processes from causing the surplus to exceed
+ * overcommit
+ *
+ * This however introduces a different race, where a process B
+ * tries to grow the static hugepage pool while alloc_pages() is
+ * called by process A. B will only examine the per-node
+ * counters in determining if surplus huge pages can be
+ * converted to normal huge pages in adjust_pool_surplus(). A
+ * won't be able to increment the per-node counter, until the
+ * lock is dropped by B, but B doesn't drop hugetlb_lock until
+ * no more huge pages can be converted from surplus to normal
+ * state (and doesn't try to convert again). Thus, we have a
+ * case where a surplus huge page exists, the pool is grown, and
+ * the surplus huge page still exists after, even though it
+ * should just have been converted to a normal huge page. This
+ * does not leak memory, though, as the hugepage will be freed
+ * once it is out of use. It also does not allow the counters to
+ * go out of whack in adjust_pool_surplus() as we don't modify
+ * the node values until we've gotten the hugepage and only the
+ * per-node value is checked there.
+ */
+ spin_lock(&hugetlb_lock);
+ if (surplus_huge_pages >= nr_overcommit_huge_pages) {
+ spin_unlock(&hugetlb_lock);
+ return NULL;
+ } else {
+ nr_huge_pages++;
+ surplus_huge_pages++;
+ }
+ spin_unlock(&hugetlb_lock);
+
page = alloc_pages(htlb_alloc_mask|__GFP_COMP|__GFP_NOWARN,
HUGETLB_PAGE_ORDER);
+
+ spin_lock(&hugetlb_lock);
if (page) {
+ nid = page_to_nid(page);
set_compound_page_dtor(page, free_huge_page);
- spin_lock(&hugetlb_lock);
- nr_huge_pages++;
- nr_huge_pages_node[page_to_nid(page)]++;
- surplus_huge_pages++;
- surplus_huge_pages_node[page_to_nid(page)]++;
- spin_unlock(&hugetlb_lock);
+ /*
+ * We incremented the global counters already
+ */
+ nr_huge_pages_node[nid]++;
+ surplus_huge_pages_node[nid]++;
+ } else {
+ nr_huge_pages--;
+ surplus_huge_pages--;
}
+ spin_unlock(&hugetlb_lock);
return page;
}
@@ -481,6 +522,12 @@ static unsigned long set_max_huge_pages(unsigned long count)
* Increase the pool size
* First take pages out of surplus state. Then make up the
* remaining difference by allocating fresh huge pages.
+ *
+ * We might race with alloc_buddy_huge_page() here and be unable
+ * to convert a surplus huge page to a normal huge page. That is
+ * not critical, though, it just means the overall size of the
+ * pool might be one hugepage larger than it needs to be, but
+ * within all the constraints specified by the sysctls.
*/
spin_lock(&hugetlb_lock);
while (surplus_huge_pages && count > persistent_huge_pages) {
@@ -509,6 +556,14 @@ static unsigned long set_max_huge_pages(unsigned long count)
* to keep enough around to satisfy reservations). Then place
* pages into surplus state as needed so the pool will shrink
* to the desired size as pages become free.
+ *
+ * By placing pages into the surplus state independent of the
+ * overcommit value, we are allowing the surplus pool size to
+ * exceed overcommit. There are few sane options here. Since
+ * alloc_buddy_huge_page() is checking the global counter,
+ * though, we'll note that we're not allowed to exceed surplus
+ * and won't grow the pool anywhere else. Not until one of the
+ * sysctls are changed, or the surplus pages go out of use.
*/
min_count = resv_huge_pages + nr_huge_pages - free_huge_pages;
min_count = max(count, min_count);