From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx188.postini.com [74.125.245.188]) by kanga.kvack.org (Postfix) with SMTP id 2CAF96B0062 for ; Thu, 25 Oct 2012 00:36:34 -0400 (EDT) Received: by mail-ia0-f169.google.com with SMTP id h37so1265245iak.14 for ; Wed, 24 Oct 2012 21:36:33 -0700 (PDT) Date: Wed, 24 Oct 2012 21:36:27 -0700 (PDT) From: Hugh Dickins Subject: Re: shmem_getpage_gfp VM_BUG_ON triggered. [3.7rc2] In-Reply-To: <20121025023738.GA27001@redhat.com> Message-ID: References: <20121025023738.GA27001@redhat.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Dave Jones Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org On Wed, 24 Oct 2012, Dave Jones wrote: > Machine under significant load (4gb memory used, swap usage fluctuating) > triggered this... > > WARNING: at mm/shmem.c:1151 shmem_getpage_gfp+0xa5c/0xa70() > Pid: 29795, comm: trinity-child4 Not tainted 3.7.0-rc2+ #49 > Call Trace: > [] warn_slowpath_common+0x7f/0xc0 > [] warn_slowpath_null+0x1a/0x20 > [] shmem_getpage_gfp+0xa5c/0xa70 > [] ? shmem_getpage_gfp+0x29e/0xa70 > [] shmem_fault+0x4f/0xa0 > [] __do_fault+0x71/0x5c0 > [] ? __lock_acquire+0x306/0x1ba0 > [] ? local_clock+0x89/0xa0 > [] handle_pte_fault+0x97/0xae0 > [] ? sub_preempt_count+0x79/0xd0 > [] ? delay_tsc+0xae/0x120 > [] ? __const_udelay+0x28/0x30 > [] handle_mm_fault+0x289/0x350 > [] __do_page_fault+0x18e/0x530 > [] ? local_clock+0x89/0xa0 > [] ? get_parent_ip+0x11/0x50 > [] ? get_parent_ip+0x11/0x50 > [] ? sub_preempt_count+0x79/0xd0 > [] ? rcu_user_exit+0xc9/0xf0 > [] do_page_fault+0x2b/0x50 > [] page_fault+0x28/0x30 > [] ? copy_user_enhanced_fast_string+0x9/0x20 > [] ? sys_futimesat+0x41/0xe0 > [] ? syscall_trace_enter+0x25/0x2c0 > [] ? tracesys+0x7e/0xe6 > [] tracesys+0xe1/0xe6 > > > > 1148 error = shmem_add_to_page_cache(page, mapping, index, > 1149 gfp, swp_to_radix_entry(swap)); > 1150 /* We already confirmed swap, and make no allocation */ > 1151 VM_BUG_ON(error); > 1152 } That's very surprising. Easy enough to handle an error there, but of course I made it a VM_BUG_ON because it violates my assumptions: I rather need to understand how this can be, and I've no idea. Clutching at straws, I expect this is entirely irrelevant, but: there isn't a warning on line 1151 of mm/shmem.c in 3.7.0-rc2 nor in current linux.git; rather, there's a VM_BUG_ON on line 1149. So you've inserted a couple of lines for some reason (more useful trinity behaviour, perhaps)? And have some config option I'm unfamiliar with, that mutates a BUG_ON or VM_BUG_ON into a warning? Hugh > > > total used free shared buffers cached > Mem: 3885528 2854064 1031464 0 9624 19208 > -/+ buffers/cache: 2825232 1060296 > Swap: 6029308 30656 5998652 -- 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