On Thu, Jan 05, 2012 at 04:35:29PM +0000, Russell King - ARM Linux wrote: > On Thu, Jan 05, 2012 at 04:17:39PM +0000, Mel Gorman wrote: > > Link please? > > Forwarded, as its still in my mailbox. > > > I'm including a patch below under development that is > > intended to only cope with the page allocator case under heavy memory > > pressure. Currently it does not pass testing because eventually RCU > > gets stalled with the following trace > > > > [ 1817.176001] [<ffffffff810214d7>] arch_trigger_all_cpu_backtrace+0x87/0xa0 > > [ 1817.176001] [<ffffffff810c4779>] __rcu_pending+0x149/0x260 > > [ 1817.176001] [<ffffffff810c48ef>] rcu_check_callbacks+0x5f/0x110 > > [ 1817.176001] [<ffffffff81068d7f>] update_process_times+0x3f/0x80 > > [ 1817.176001] [<ffffffff8108c4eb>] tick_sched_timer+0x5b/0xc0 > > [ 1817.176001] [<ffffffff8107f28e>] __run_hrtimer+0xbe/0x1a0 > > [ 1817.176001] [<ffffffff8107f581>] hrtimer_interrupt+0xc1/0x1e0 > > [ 1817.176001] [<ffffffff81020ef3>] smp_apic_timer_interrupt+0x63/0xa0 > > [ 1817.176001] [<ffffffff81449073>] apic_timer_interrupt+0x13/0x20 > > [ 1817.176001] [<ffffffff8116c135>] vfsmount_lock_local_lock+0x25/0x30 > > [ 1817.176001] [<ffffffff8115c855>] path_init+0x2d5/0x370 > > [ 1817.176001] [<ffffffff8115eecd>] path_lookupat+0x2d/0x620 > > [ 1817.176001] [<ffffffff8115f4ef>] do_path_lookup+0x2f/0xd0 > > [ 1817.176001] [<ffffffff811602af>] user_path_at_empty+0x9f/0xd0 > > [ 1817.176001] [<ffffffff81154e7b>] vfs_fstatat+0x4b/0x90 > > [ 1817.176001] [<ffffffff81154f4f>] sys_newlstat+0x1f/0x50 > > [ 1817.176001] [<ffffffff81448692>] system_call_fastpath+0x16/0x1b > > > > It might be a separate bug, don't know for sure. Do you get multiple RCU CPU stall-warning messages? If so, it can be helpful to look at how the stack frame changes over time. These stalls are normally caused by a loop in the kernel with preemption disabled, though other scenarios can also cause them. I am assuming that the CPU is reporting a stall on itself in this case. If not, then it is necessary to look at the stack of the CPU that the stall is being reported for. Thanx, Paul > I'm not going to even pretend to understand what the above backtrace > means: it doesn't look like what I'd expect from the problem which > PeterZ's patch is supposed to address. It certainly doesn't do anything > to address the cpu-going-offline problem you seem to have found. > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>