From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-x443.google.com (mail-pf1-x443.google.com [IPv6:2607:f8b0:4864:20::443]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id 2505621197B20 for ; Tue, 19 Mar 2019 01:44:44 -0700 (PDT) Received: by mail-pf1-x443.google.com with SMTP id i19so13225578pfd.0 for ; Tue, 19 Mar 2019 01:44:44 -0700 (PDT) Date: Tue, 19 Mar 2019 11:44:39 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH 2/2] mm/dax: Don't enable huge dax mapping by default Message-ID: <20190319084439.eya2pisiirattuil@kshutemo-mobl1> References: <20190228083522.8189-1-aneesh.kumar@linux.ibm.com> <20190228083522.8189-2-aneesh.kumar@linux.ibm.com> <87k1hc8iqa.fsf@linux.ibm.com> <20190306124453.126d36d8@naga.suse.cz> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" To: Dan Williams Cc: Jan Kara , linux-nvdimm , "Aneesh Kumar K.V" , Linux Kernel Mailing List , Linux MM , Ross Zwisler , Andrew Morton , Michal =?utf-8?B?U3VjaMOhbmVr?= , linuxppc-dev , "Kirill A . Shutemov" List-ID: On Wed, Mar 13, 2019 at 09:07:13AM -0700, Dan Williams wrote: > On Wed, Mar 6, 2019 at 4:46 AM Aneesh Kumar K.V > wrote: > > > > On 3/6/19 5:14 PM, Michal Such=E1nek wrote: > > > On Wed, 06 Mar 2019 14:47:33 +0530 > > > "Aneesh Kumar K.V" wrote: > > > > > >> Dan Williams writes: > > >> > > >>> On Thu, Feb 28, 2019 at 1:40 AM Oliver wrote: > > >>>> > > >>>> On Thu, Feb 28, 2019 at 7:35 PM Aneesh Kumar K.V > > >>>> wrote: > > > > > >> Also even if the user decided to not use THP, by > > >> echo "never" > transparent_hugepage/enabled , we should continue to = map > > >> dax fault using huge page on platforms that can support huge pages. > > > > > > Is this a good idea? > > > > > > This knob is there for a reason. In some situations having huge pages > > > can severely impact performance of the system (due to host-guest > > > interaction or whatever) and the ability to really turn off all THP > > > would be important in those cases, right? > > > > > > > My understanding was that is not true for dax pages? These are not > > regular memory that got allocated. They are allocated out of /dev/dax/ > > or /dev/pmem*. Do we have a reason not to use hugepages for mapping > > pages in that case? > = > The problem with the transparent_hugepage/enabled interface is that it > conflates performing compaction work to produce THP-pages with the > ability to map huge pages at all. That's not [entirely] true. transparent_hugepage/defrag gates heavy-duty compaction. We do only very limited compaction if it's not advised by transparent_hugepage/defrag. I believe DAX has to respect transparent_hugepage/enabled. Or not advertise its huge pages as THP. It's confusing for user. -- = Kirill A. Shutemov _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm