From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f70.google.com (mail-it0-f70.google.com [209.85.214.70]) by kanga.kvack.org (Postfix) with ESMTP id 7F1476B005A for ; Wed, 28 Mar 2018 06:17:00 -0400 (EDT) Received: by mail-it0-f70.google.com with SMTP id w125-v6so2008126itf.0 for ; Wed, 28 Mar 2018 03:17:00 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id u66-v6sor1647568itd.102.2018.03.28.03.16.59 for (Google Transport Security); Wed, 28 Mar 2018 03:16:59 -0700 (PDT) Date: Wed, 28 Mar 2018 03:16:55 -0700 (PDT) From: David Rientjes Subject: Re: [PATCH v9 01/24] mm: Introduce CONFIG_SPECULATIVE_PAGE_FAULT In-Reply-To: <32c80b6a-28c6-bf63-ed7b-6a042ae18e8f@linux.vnet.ibm.com> Message-ID: References: <1520963994-28477-1-git-send-email-ldufour@linux.vnet.ibm.com> <1520963994-28477-2-git-send-email-ldufour@linux.vnet.ibm.com> <32c80b6a-28c6-bf63-ed7b-6a042ae18e8f@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Laurent Dufour Cc: Thomas Gleixner , paulmck@linux.vnet.ibm.com, peterz@infradead.org, akpm@linux-foundation.org, kirill@shutemov.name, ak@linux.intel.com, mhocko@kernel.org, dave@stgolabs.net, jack@suse.cz, Matthew Wilcox , benh@kernel.crashing.org, mpe@ellerman.id.au, paulus@samba.org, Ingo Molnar , hpa@zytor.com, Will Deacon , Sergey Senozhatsky , Andrea Arcangeli , Alexei Starovoitov , kemi.wang@intel.com, sergey.senozhatsky.work@gmail.com, Daniel Jordan , 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 , linuxppc-dev@lists.ozlabs.org, x86@kernel.org On Wed, 28 Mar 2018, 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. > >> > >> Suggested-by: Thomas Gleixner > >> Signed-off-by: Laurent Dufour > >> --- > >> mm/Kconfig | 3 +++ > >> 1 file changed, 3 insertions(+) > >> > >> diff --git a/mm/Kconfig b/mm/Kconfig > >> index abefa573bcd8..07c566c88faf 100644 > >> --- a/mm/Kconfig > >> +++ b/mm/Kconfig > >> @@ -759,3 +759,6 @@ config GUP_BENCHMARK > >> performance of get_user_pages_fast(). > >> > >> See tools/testing/selftests/vm/gup_benchmark.c > >> + > >> +config SPECULATIVE_PAGE_FAULT > >> + bool > > > > Should this be configurable even if the arch supports it? > > Actually, this is not configurable unless by manually editing the .config file. > > I made it this way on the Thomas's request : > https://lkml.org/lkml/2018/1/15/969 > > That sounds to be the smarter way to achieve that, isn't it ? > Putting this in mm/Kconfig is definitely the right way to go about it instead of any generic option in arch/*. My question, though, was making this configurable by the user: config SPECULATIVE_PAGE_FAULT bool "Speculative page faults" depends on X86_64 || PPC default y help .. It's a question about whether we want this always enabled on x86_64 and power or whether the user should be able to disable it (right now they can't). With a large feature like this, you may want to offer something simple (disable CONFIG_SPECULATIVE_PAGE_FAULT) if someone runs into regressions.