From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx186.postini.com [74.125.245.186]) by kanga.kvack.org (Postfix) with SMTP id 495126B0078 for ; Fri, 21 Dec 2012 19:36:43 -0500 (EST) Received: by mail-vb0-f44.google.com with SMTP id fc26so5766441vbb.17 for ; Fri, 21 Dec 2012 16:36:42 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <1356050997-2688-1-git-send-email-walken@google.com> References: <1356050997-2688-1-git-send-email-walken@google.com> From: Andy Lutomirski Date: Fri, 21 Dec 2012 16:36:21 -0800 Message-ID: Subject: Re: [PATCH 0/9] Avoid populating unbounded num of ptes with mmap_sem held Content-Type: text/plain; charset=ISO-8859-1 Sender: owner-linux-mm@kvack.org List-ID: To: Michel Lespinasse Cc: Ingo Molnar , Al Viro , Hugh Dickins , Jorn_Engel , Rik van Riel , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org On Thu, Dec 20, 2012 at 4:49 PM, Michel Lespinasse wrote: > We have many vma manipulation functions that are fast in the typical case, > but can optionally be instructed to populate an unbounded number of ptes > within the region they work on: > - mmap with MAP_POPULATE or MAP_LOCKED flags; > - remap_file_pages() with MAP_NONBLOCK not set or when working on a > VM_LOCKED vma; > - mmap_region() and all its wrappers when mlock(MCL_FUTURE) is in effect; > - brk() when mlock(MCL_FUTURE) is in effect. > Something's buggy here. My evil test case is stuck with lots of threads spinning at 100% system time. Stack traces look like: [<0000000000000000>] __mlock_vma_pages_range+0x66/0x70 [<0000000000000000>] __mm_populate+0xf9/0x150 [<0000000000000000>] vm_mmap_pgoff+0x9f/0xc0 [<0000000000000000>] sys_mmap_pgoff+0x7e/0x150 [<0000000000000000>] sys_mmap+0x22/0x30 [<0000000000000000>] system_call_fastpath+0x16/0x1b [<0000000000000000>] 0xffffffffffffffff perf top says: 38.45% [kernel] [k] __mlock_vma_pages_range 33.04% [kernel] [k] __get_user_pages 28.18% [kernel] [k] __mm_populate The tasks in question use MCL_FUTURE but not MAP_POPULATE. These tasks are immune to SIGKILL. --Andy -- 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