From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0a-001b2d01.pphosted.com [148.163.156.1]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 40qv5S6y03zDqlr for ; Tue, 22 May 2018 21:47:24 +1000 (AEST) Received: from pps.filterd (m0098399.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id w4MBcwPi089130 for ; Tue, 22 May 2018 07:47:22 -0400 Received: from e06smtp14.uk.ibm.com (e06smtp14.uk.ibm.com [195.75.94.110]) by mx0a-001b2d01.pphosted.com with ESMTP id 2j4j299nq3-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Tue, 22 May 2018 07:47:22 -0400 Received: from localhost by e06smtp14.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 22 May 2018 12:47:19 +0100 Subject: Re: [PATCH v11 01/26] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT To: Randy Dunlap , akpm@linux-foundation.org, mhocko@kernel.org, peterz@infradead.org, kirill@shutemov.name, ak@linux.intel.com, dave@stgolabs.net, jack@suse.cz, Matthew Wilcox , khandual@linux.vnet.ibm.com, aneesh.kumar@linux.vnet.ibm.com, benh@kernel.crashing.org, mpe@ellerman.id.au, paulus@samba.org, Thomas Gleixner , Ingo Molnar , hpa@zytor.com, Will Deacon , Sergey Senozhatsky , sergey.senozhatsky.work@gmail.com, Andrea Arcangeli , Alexei Starovoitov , kemi.wang@intel.com, Daniel Jordan , David Rientjes , Jerome Glisse , Ganesh Mahendran , Minchan Kim , Punit Agrawal , vinayak menon , Yang Shi Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, haren@linux.vnet.ibm.com, npiggin@gmail.com, bsingharora@gmail.com, paulmck@linux.vnet.ibm.com, Tim Chen , linuxppc-dev@lists.ozlabs.org, x86@kernel.org References: <1526555193-7242-1-git-send-email-ldufour@linux.vnet.ibm.com> <1526555193-7242-2-git-send-email-ldufour@linux.vnet.ibm.com> <2cb8256d-5822-d94d-b0e6-c46f21d84852@infradead.org> From: Laurent Dufour Date: Tue, 22 May 2018 13:47:08 +0200 MIME-Version: 1.0 In-Reply-To: <2cb8256d-5822-d94d-b0e6-c46f21d84852@infradead.org> Content-Type: text/plain; charset=utf-8 Message-Id: <8a4016fb-2c2f-ad9a-9dd4-0ed3e664b659@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 17/05/2018 18:36, Randy Dunlap wrote: > Hi, > > On 05/17/2018 04:06 AM, Laurent Dufour wrote: >> This configuration variable will be used to build the code needed to >> handle speculative page fault. >> >> By default it is turned off, and activated depending on architecture >> support, ARCH_HAS_PTE_SPECIAL, SMP and MMU. >> >> The architecture support is needed since the speculative page fault handler >> is called from the architecture's page faulting code, and some code has to >> be added there to handle the speculative handler. >> >> The dependency on ARCH_HAS_PTE_SPECIAL is required because vm_normal_page() >> does processing that is not compatible with the speculative handling in the >> case ARCH_HAS_PTE_SPECIAL is not set. >> >> Suggested-by: Thomas Gleixner >> Suggested-by: David Rientjes >> Signed-off-by: Laurent Dufour >> --- >> mm/Kconfig | 22 ++++++++++++++++++++++ >> 1 file changed, 22 insertions(+) >> >> diff --git a/mm/Kconfig b/mm/Kconfig >> index 1d0888c5b97a..a38796276113 100644 >> --- a/mm/Kconfig >> +++ b/mm/Kconfig >> @@ -761,3 +761,25 @@ config GUP_BENCHMARK >> >> config ARCH_HAS_PTE_SPECIAL >> bool >> + >> +config ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT >> + def_bool n >> + >> +config SPECULATIVE_PAGE_FAULT >> + bool "Speculative page faults" >> + default y >> + depends on ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT >> + depends on ARCH_HAS_PTE_SPECIAL && MMU && SMP >> + help >> + Try to handle user space page faults without holding the mmap_sem. >> + >> + This should allow better concurrency for massively threaded process > > processes > >> + since the page fault handler will not wait for other threads memory > > thread's > >> + layout change to be done, assuming that this change is done in another >> + part of the process's memory space. This type of page fault is named >> + speculative page fault. >> + >> + If the speculative page fault fails because of a concurrency is > > because a concurrency is > >> + detected or because underlying PMD or PTE tables are not yet >> + allocating, it is failing its processing and a classic page fault > > allocated, the speculative page fault fails and a classic page fault > >> + is then tried. > > > Also, all of the help text (below the "help" line) should be indented by > 1 tab + 2 spaces (in coding-style.rst). Thanks, Randy for reviewing my miserable English grammar. I'll fix that and the indentation.