From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f199.google.com (mail-wr0-f199.google.com [209.85.128.199]) by kanga.kvack.org (Postfix) with ESMTP id C5D536B0311 for ; Thu, 6 Jul 2017 11:29:37 -0400 (EDT) Received: by mail-wr0-f199.google.com with SMTP id 23so1487007wry.4 for ; Thu, 06 Jul 2017 08:29:37 -0700 (PDT) Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com. [148.163.158.5]) by mx.google.com with ESMTPS id j1si209133wrb.194.2017.07.06.08.29.35 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 06 Jul 2017 08:29:36 -0700 (PDT) Received: from pps.filterd (m0098413.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v66FSgf2054232 for ; Thu, 6 Jul 2017 11:29:34 -0400 Received: from e06smtp15.uk.ibm.com (e06smtp15.uk.ibm.com [195.75.94.111]) by mx0b-001b2d01.pphosted.com with ESMTP id 2bhqu705x1-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Thu, 06 Jul 2017 11:29:34 -0400 Received: from localhost by e06smtp15.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 6 Jul 2017 16:29:32 +0100 Subject: Re: [RFC v5 09/11] mm: Try spin lock in speculative path References: <1497635555-25679-1-git-send-email-ldufour@linux.vnet.ibm.com> <1497635555-25679-10-git-send-email-ldufour@linux.vnet.ibm.com> <20170705185023.xlqko7wgepwsny5g@hirez.programming.kicks-ass.net> <3af22f3b-03ab-1d37-b2b1-b616adde7eb6@linux.vnet.ibm.com> <20170706144852.fwtuygj4ikcjmqat@hirez.programming.kicks-ass.net> From: Laurent Dufour Date: Thu, 6 Jul 2017 17:29:26 +0200 MIME-Version: 1.0 In-Reply-To: <20170706144852.fwtuygj4ikcjmqat@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Message-Id: Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: paulmck@linux.vnet.ibm.com, akpm@linux-foundation.org, kirill@shutemov.name, ak@linux.intel.com, mhocko@kernel.org, dave@stgolabs.net, jack@suse.cz, Matthew Wilcox , linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, khandual@linux.vnet.ibm.com, npiggin@gmail.com, bsingharora@gmail.com, Tim Chen On 06/07/2017 16:48, Peter Zijlstra wrote: > On Thu, Jul 06, 2017 at 03:46:59PM +0200, Laurent Dufour wrote: >> On 05/07/2017 20:50, Peter Zijlstra wrote: >>> On Fri, Jun 16, 2017 at 07:52:33PM +0200, Laurent Dufour wrote: >>>> @@ -2294,8 +2295,19 @@ static bool pte_map_lock(struct vm_fault *vmf) >>>> if (vma_has_changed(vmf->vma, vmf->sequence)) >>>> goto out; >>>> >>>> - pte = pte_offset_map_lock(vmf->vma->vm_mm, vmf->pmd, >>>> - vmf->address, &ptl); > >>>> + ptl = pte_lockptr(vmf->vma->vm_mm, vmf->pmd); >>>> + pte = pte_offset_map(vmf->pmd, vmf->address); >>>> + if (unlikely(!spin_trylock(ptl))) { >>>> + pte_unmap(pte); >>>> + goto out; >>>> + } >>>> + >>>> if (vma_has_changed(vmf->vma, vmf->sequence)) { >>>> pte_unmap_unlock(pte, ptl); >>>> goto out; >>> >>> Right, so if you look at my earlier patches you'll see I did something >>> quite disgusting here. >>> >>> Not sure that wants repeating, but I cannot remember why I thought this >>> deadlock didn't exist anymore. >> >> Regarding the deadlock I did face it on my Power victim node, so I guess it >> is still there, and the stack traces are quiet explicit. >> Am I missing something here ? > > No, you are right in that the deadlock is quite real. What I cannot > remember is what made me think to remove the really 'wonderful' code I > had to deal with it. > > That said, you might want to look at how often you terminate the > speculation because of your trylock failing. If that shows up at all we > might need to do something about it. Based on the benchmarks I run, it doesn't fail so much often, but I was thinking about adding some counters here. The system is accounting for major page faults and minor ones, respectively current->maj_flt and current->min_flt. I was wondering if an additional type like async_flt will be welcome or if there is another smarter way to get that metric. Feel free to advise. Thanks Laurent. -- 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