From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) (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 40mxl35HZ6zF25l for ; Fri, 18 May 2018 02:36:15 +1000 (AEST) Subject: Re: [PATCH v11 01/26] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT To: Laurent Dufour , 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> From: Randy Dunlap Message-ID: <2cb8256d-5822-d94d-b0e6-c46f21d84852@infradead.org> Date: Thu, 17 May 2018 09:36:00 -0700 MIME-Version: 1.0 In-Reply-To: <1526555193-7242-2-git-send-email-ldufour@linux.vnet.ibm.com> Content-Type: text/plain; charset=utf-8 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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). -- ~Randy