From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751392AbeDWF6W (ORCPT ); Mon, 23 Apr 2018 01:58:22 -0400 Received: from mail-pf0-f194.google.com ([209.85.192.194]:35032 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750852AbeDWF6V (ORCPT ); Mon, 23 Apr 2018 01:58:21 -0400 X-Google-Smtp-Source: AIpwx486wjYwg2ifBAZkGZLt1h7lQAcxnkOSEdu0NmrO0Y9oJDQ4KzZOr67rXwzLdM3RpKHDcWn9yQ== Date: Mon, 23 Apr 2018 14:58:09 +0900 From: Minchan Kim To: Laurent Dufour Cc: 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 , benh@kernel.crashing.org, mpe@ellerman.id.au, paulus@samba.org, Thomas Gleixner , Ingo Molnar , hpa@zytor.com, Will Deacon , Sergey Senozhatsky , Andrea Arcangeli , Alexei Starovoitov , kemi.wang@intel.com, sergey.senozhatsky.work@gmail.com, Daniel Jordan , David Rientjes , Jerome Glisse , Ganesh Mahendran , 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, paulmck@linux.vnet.ibm.com, Tim Chen , linuxppc-dev@lists.ozlabs.org, x86@kernel.org Subject: Re: [PATCH v10 01/25] mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT Message-ID: <20180423055809.GA114098@rodete-desktop-imager.corp.google.com> References: <1523975611-15978-1-git-send-email-ldufour@linux.vnet.ibm.com> <1523975611-15978-2-git-send-email-ldufour@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1523975611-15978-2-git-send-email-ldufour@linux.vnet.ibm.com> User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Laurent, I guess it's good timing to review. Guess LSF/MM goes so might change a lot since then. :) Anyway, I grap a time to review. On Tue, Apr 17, 2018 at 04:33:07PM +0200, 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, SMP and MMU. Can we have description in here why it depends on architecture? > > 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 d5004d82a1d6..5484dca11199 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -752,3 +752,25 @@ config GUP_BENCHMARK > performance of get_user_pages_fast(). > > See tools/testing/selftests/vm/gup_benchmark.c > + > +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 MMU && SMP > + help > + Try to handle user space page faults without holding the mmap_sem. > + > + This should allow better concurrency for massively threaded process > + since the page fault handler will not wait for other threads memory > + 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 > + detected or because underlying PMD or PTE tables are not yet > + allocating, it is failing its processing and a classic page fault > + is then tried. > -- > 2.7.4 >