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authorLarry Woodman <lwoodman@redhat.com>2008-01-24 05:49:25 -0800
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2008-01-24 08:07:27 -0800
commitc5c99429fa57dcf6e05203ebe3676db1ec646793 (patch)
tree0be05b59713e87a42274c0fe76da48f423f148e1
parentc2f3dabefa73fe3307578553f456e93f0a1bca08 (diff)
fix hugepages leak due to pagetable page sharing
The shared page table code for hugetlb memory on x86 and x86_64 is causing a leak. When a user of hugepages exits using this code the system leaks some of the hugepages. ------------------------------------------------------- Part of /proc/meminfo just before database startup: HugePages_Total: 5500 HugePages_Free: 5500 HugePages_Rsvd: 0 Hugepagesize: 2048 kB Just before shutdown: HugePages_Total: 5500 HugePages_Free: 4475 HugePages_Rsvd: 0 Hugepagesize: 2048 kB After shutdown: HugePages_Total: 5500 HugePages_Free: 4988 HugePages_Rsvd: 0 Hugepagesize: 2048 kB ---------------------------------------------------------- The problem occurs durring a fork, in copy_hugetlb_page_range(). It locates the dst_pte using huge_pte_alloc(). Since huge_pte_alloc() calls huge_pmd_share() it will share the pmd page if can, yet the main loop in copy_hugetlb_page_range() does a get_page() on every hugepage. This is a violation of the shared hugepmd pagetable protocol and creates additional referenced to the hugepages causing a leak when the unmap of the VMA occurs. We can skip the entire replication of the ptes when the hugepage pagetables are shared. The attached patch skips copying the ptes and the get_page() calls if the hugetlbpage pagetable is shared. [akpm@linux-foundation.org: coding-style cleanups] Signed-off-by: Larry Woodman <lwoodman@redhat.com> Signed-off-by: Adam Litke <agl@us.ibm.com> Cc: Badari Pulavarty <pbadari@us.ibm.com> Cc: Ken Chen <kenchen@google.com> Cc: David Gibson <david@gibson.dropbear.id.au> Cc: William Lee Irwin III <wli@holomorphy.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/hugetlb.c5
1 files changed, 5 insertions, 0 deletions
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index e0fda156f021..db861d8b6c28 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -699,6 +699,11 @@ int copy_hugetlb_page_range(struct mm_struct *dst, struct mm_struct *src,
dst_pte = huge_pte_alloc(dst, addr);
if (!dst_pte)
goto nomem;
+
+ /* If the pagetables are shared don't copy or take references */
+ if (dst_pte == src_pte)
+ continue;
+
spin_lock(&dst->page_table_lock);
spin_lock(&src->page_table_lock);
if (!pte_none(*src_pte)) {