diff options
Diffstat (limited to 'mm/hugetlb.c')
| -rw-r--r-- | mm/hugetlb.c | 67 |
1 files changed, 61 insertions, 6 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 6f97821..3a79065 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); |
