From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 4E6C76B01BB for ; Fri, 28 May 2010 01:50:58 -0400 (EDT) Received: by gyg4 with SMTP id 4so720551gyg.14 for ; Thu, 27 May 2010 22:50:56 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20100528143605.7E2A.A69D9226@jp.fujitsu.com> References: <20100528134133.7E24.A69D9226@jp.fujitsu.com> <20100528143605.7E2A.A69D9226@jp.fujitsu.com> Date: Fri, 28 May 2010 14:50:55 +0900 Message-ID: Subject: Re: [RFC] oom-kill: give the dying task a higher priority From: Minchan Kim Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: KOSAKI Motohiro Cc: balbir@linux.vnet.ibm.com, "Luis Claudio R. Goncalves" , Oleg Nesterov , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Thomas Gleixner , Peter Zijlstra , David Rientjes , Mel Gorman , williams@redhat.com List-ID: On Fri, May 28, 2010 at 2:39 PM, KOSAKI Motohiro wrote: > Hi > >> Hi, Kosaki. >> >> On Fri, May 28, 2010 at 1:46 PM, KOSAKI Motohiro >> wrote: >> >> * Luis Claudio R. Goncalves [2010-05-28 00:51:47]= : >> >> >> >> > @@ -382,6 +382,8 @@ static void dump_header(struct task_struct *p, = gfp_t gfp_mask, int order, >> >> > =C2=A0 */ >> >> > =C2=A0static void __oom_kill_task(struct task_struct *p, int verbos= e) >> >> > =C2=A0{ >> >> > + =C2=A0 struct sched_param param; >> >> > + >> >> > =C2=A0 =C2=A0 if (is_global_init(p)) { >> >> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 WARN_ON(1); >> >> > =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 printk(KERN_WARNING "trie= d to kill init!\n"); >> >> > @@ -413,8 +415,9 @@ static void __oom_kill_task(struct task_struct = *p, int verbose) >> >> > =C2=A0 =C2=A0 =C2=A0*/ >> >> > =C2=A0 =C2=A0 p->rt.time_slice =3D HZ; >> >> > =C2=A0 =C2=A0 set_tsk_thread_flag(p, TIF_MEMDIE); >> >> > - >> >> > =C2=A0 =C2=A0 force_sig(SIGKILL, p); >> >> > + =C2=A0 param.sched_priority =3D MAX_RT_PRIO-1; >> >> > + =C2=A0 sched_setscheduler_nocheck(p, SCHED_FIFO, ¶m); >> >> > =C2=A0} >> >> > >> >> >> >> I would like to understand the visible benefits of this patch. Have >> >> you seen an OOM kill tasked really get bogged down. Should this task >> >> really be competing with other important tasks for run time? >> > >> > What you mean important? Until OOM victim task exit completely, the sy= stem have no memory. >> > all of important task can't do anything. >> > >> > In almost kernel subsystems, automatically priority boost is really ba= d idea because >> > it may break RT task's deterministic behavior. but OOM is one of excep= tion. The deterministic >> > was alread broken by memory starvation. >> >> Yes or No. >> >> IMHO, normally RT tasks shouldn't use dynamic allocation(ie, >> non-deterministic functions or system calls) in place which is needed >> deterministic. So memory starvation might not break real-time >> deterministic. > > I think It's impossible. Normally RT task use mlock and it prevent almost= page > allocation. but every syscall internally call kmalloc(). They can't avoid > it practically. > > How do you perfectly avoid dynamic allocation? RT Task void non-RT-function() { system call(); buffer =3D malloc(); memset(buffer); } /* * We make sure this function must be executed in some millisecond */ void RT-function() { some calculation(); <- This doesn't have no dynamic characteristic } int main() { non-RT-function(); /* This function make sure RT-function cannot preempt by others */ set_RT_max_high_priority(); RT-function A(); set_normal_priority(); non-RT-function(); } We don't want realtime in whole function of the task. What we want is just RT-function A. Of course, current Linux cannot make perfectly sure RT-functionA can not preempt by others. That's because some interrupt or exception happen. But RT-function A doesn't related to any dynamic characteristic. What can justify to preempt RT-function A by other processes? --=20 Kind regards, Minchan Kim -- 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