Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758338AbZJFXAW (ORCPT ); Tue, 6 Oct 2009 19:00:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756920AbZJFXAV (ORCPT ); Tue, 6 Oct 2009 19:00:21 -0400 Received: from smtp-out.google.com ([216.239.45.13]:30435 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753663AbZJFXAU convert rfc822-to-8bit (ORCPT ); Tue, 6 Oct 2009 19:00:20 -0400 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=mime-version:in-reply-to:references:date:message-id:subject:from:to: cc:content-type:content-transfer-encoding:x-system-of-record; b=R99bv2+xeDueJxIFgDJNTmzcjoR8KfDdGPYmvEi+uBnZo1JQtIpANiMlkX9bNkeDE yEjC8VLbe1ScnDISyJ4QQ== MIME-Version: 1.0 In-Reply-To: <20091006114052.5FAA.A69D9226@jp.fujitsu.com> References: <20091006112803.5FA5.A69D9226@jp.fujitsu.com> <20091006114052.5FAA.A69D9226@jp.fujitsu.com> Date: Tue, 6 Oct 2009 15:59:09 -0700 Message-ID: <604427e00910061559v34590d49x4cdd01b16df6fb1e@mail.gmail.com> Subject: Re: [PATCH 2/2] mlock use lru_add_drain_all_async() From: Ying Han To: KOSAKI Motohiro Cc: LKML , linux-mm , Andrew Morton , Peter Zijlstra , Oleg Nesterov , Christoph Lameter Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT X-System-Of-Record: true Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2798 Lines: 76 Hello?KOSAKI-san, Few questions on the lru_add_drain_all_async(). If i understand correctly, the reason that we have lru_add_drain_all() in the mlock() call is to isolate mlocked pages into the separate LRU in case they are sitting in pagevec. And I also understand the RT use cases you put in the patch description, now my questions is that do we have race after applying the patch? For example that if the RT task not giving up the cpu by the time mlock returns, you have pages left in the pagevec which not being drained back to the lru list. Do we have problem with that? --Ying On Mon, Oct 5, 2009 at 7:41 PM, KOSAKI Motohiro wrote: > > Recently, Peter Zijlstra reported RT-task can lead to prevent mlock > very long time. > > ?Suppose you have 2 cpus, cpu1 is busy doing a SCHED_FIFO-99 while(1), > ?cpu0 does mlock()->lru_add_drain_all(), which does > ?schedule_on_each_cpu(), which then waits for all cpus to complete the > ?work. Except that cpu1, which is busy with the RT task, will never run > ?keventd until the RT load goes away. > > ?This is not so much an actual deadlock as a serious starvation case. > > Actually, mlock() doesn't need to wait to finish lru_add_drain_all(). > Thus, this patch replace it with lru_add_drain_all_async(). > > Cc: Oleg Nesterov > Reported-by: Peter Zijlstra > Signed-off-by: KOSAKI Motohiro > --- > ?mm/mlock.c | ? ?4 ++-- > ?1 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/mlock.c b/mm/mlock.c > index 22041aa..46a016f 100644 > --- a/mm/mlock.c > +++ b/mm/mlock.c > @@ -458,7 +458,7 @@ SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len) > ? ? ? ?if (!can_do_mlock()) > ? ? ? ? ? ? ? ?return -EPERM; > > - ? ? ? lru_add_drain_all(); ? ?/* flush pagevec */ > + ? ? ? lru_add_drain_all_async(); ? ? ?/* flush pagevec */ > > ? ? ? ?down_write(¤t->mm->mmap_sem); > ? ? ? ?len = PAGE_ALIGN(len + (start & ~PAGE_MASK)); > @@ -526,7 +526,7 @@ SYSCALL_DEFINE1(mlockall, int, flags) > ? ? ? ?if (!can_do_mlock()) > ? ? ? ? ? ? ? ?goto out; > > - ? ? ? lru_add_drain_all(); ? ?/* flush pagevec */ > + ? ? ? lru_add_drain_all_async(); ? ? ?/* flush pagevec */ > > ? ? ? ?down_write(¤t->mm->mmap_sem); > > -- > 1.6.2.5 > > > > -- > 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/