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[192.55.54.39]) by smtp.gmail.com with ESMTPSA id h10sm3128992pfo.128.2019.03.06.05.06.25 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 06 Mar 2019 05:06:25 -0800 (PST) Received: by kshutemo-mobl1.localdomain (Postfix, from userid 1000) id 98357301186; Wed, 6 Mar 2019 16:06:21 +0300 (+03) Date: Wed, 6 Mar 2019 16:06:21 +0300 From: "Kirill A. Shutemov" To: "Aneesh Kumar K.V" Cc: Michal =?utf-8?B?U3VjaMOhbmVr?= , Dan Williams , Oliver , Jan Kara , linux-nvdimm@lists.01.org, Linux Kernel Mailing List , Linux MM , Ross Zwisler , Andrew Morton , linuxppc-dev , "Kirill A . Shutemov" Subject: Re: [PATCH 2/2] mm/dax: Don't enable huge dax mapping by default Message-ID: <20190306130621.qrwybv5dpv3bzyym@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-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: NeoMutt/20180716 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 06, 2019 at 06:15:25PM +0530, Aneesh Kumar K.V wrote: > On 3/6/19 5:14 PM, Michal Suchánek 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? Yes. Like when you don't want dax to compete for TLB with mission-critical application (which uses hugetlb for instance). -- Kirill A. Shutemov