From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932815Ab1KHXB5 (ORCPT ); Tue, 8 Nov 2011 18:01:57 -0500 Received: from mx1.redhat.com ([209.132.183.28]:41307 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753687Ab1KHXBz (ORCPT ); Tue, 8 Nov 2011 18:01:55 -0500 Date: Wed, 9 Nov 2011 01:01:46 +0100 From: Andrea Arcangeli To: "Srivatsa S. Bhat" Cc: "Rafael J. Wysocki" , linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, Jiri Slaby , linux-mm@kvack.org, Andrew Morton Subject: Re: [PATCH] thp: reduce khugepaged freezing latency Message-ID: <20111109000146.GA5075@redhat.com> References: <4EB8E969.6010502@suse.cz> <1320766151-2619-1-git-send-email-aarcange@redhat.com> <1320766151-2619-2-git-send-email-aarcange@redhat.com> <4EB98A83.3040101@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4EB98A83.3040101@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 09, 2011 at 01:31:07AM +0530, Srivatsa S. Bhat wrote: > On 11/08/2011 08:59 PM, Andrea Arcangeli wrote: > > Lack of set_freezable_with_signal() prevented khugepaged to be waken > > up (and prevented to sleep again) across the > > schedule_timeout_interruptible() calls after freezing() becomes > > true. The tight loop in khugepaged_alloc_hugepage() also missed one > > try_to_freeze() call in case alloc_hugepage() would repeatedly fail in > > turn preventing the loop to break and to reach the try_to_freeze() in > > the khugepaged main loop. > > > > khugepaged would still freeze just fine by trying again the next > > minute but it's better if it freezes immediately. > > > > Reported-by: Jiri Slaby > > Signed-off-by: Andrea Arcangeli > > --- > > mm/huge_memory.c | 3 ++- > > 1 files changed, 2 insertions(+), 1 deletions(-) > > > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > > index 4298aba..67311d1 100644 > > --- a/mm/huge_memory.c > > +++ b/mm/huge_memory.c > > @@ -2277,6 +2277,7 @@ static struct page *khugepaged_alloc_hugepage(void) > > if (!hpage) { > > count_vm_event(THP_COLLAPSE_ALLOC_FAILED); > > khugepaged_alloc_sleep(); > > + try_to_freeze(); > > } else > > count_vm_event(THP_COLLAPSE_ALLOC); > > } while (unlikely(!hpage) && > > @@ -2331,7 +2332,7 @@ static int khugepaged(void *none) > > { > > struct mm_slot *mm_slot; > > > > - set_freezable(); > > + set_freezable_with_signal(); > > set_user_nice(current, 19); > > > > /* serialize with start_khugepaged() */ > > > > Why do we need to use both set_freezable_with_signal() and an additional > try_to_freeze()? Won't just using either one of them be good enough? > Or am I missing something here? set_freezable_with_signal() makes khugepaged quit and not re-enter the sleep, try_to_freeze is needed to get the task from freezing to frozen, otherwise it'll loop without getting frozen.