From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <478F74A2.9090406@redhat.com> Date: Thu, 17 Jan 2008 10:30:42 -0500 From: Larry Woodman MIME-Version: 1.0 Subject: [PATCH] fix hugepages leak due to pagetable page sharing. Content-Type: multipart/mixed; boundary="------------080803000409090203020307" Sender: owner-linux-mm@kvack.org Return-Path: To: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org List-ID: This is a multi-part message in MIME format. --------------080803000409090203020307 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit 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. Signed-off-by: Larry Woodman --------------080803000409090203020307 Content-Type: text/plain; name="linux-shared.patch" Content-Transfer-Encoding: 7bit Content-Disposition: inline; filename="linux-shared.patch" --- linux-2.6.23/mm/hugetlb.c.orig 2008-01-16 12:05:41.496448000 -0500 +++ linux-2.6.23/mm/hugetlb.c 2008-01-17 10:27:21.740353000 -0500 @@ -377,6 +377,11 @@ int copy_hugetlb_page_range(struct mm_st dst_pte = huge_pte_alloc(dst, addr); if (!dst_pte) goto nomem; + + /* if the pagetables are shared dont 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)) { --------------080803000409090203020307-- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org