From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f179.google.com (mail-pf0-f179.google.com [209.85.192.179]) by kanga.kvack.org (Postfix) with ESMTP id E08CD6B0009 for ; Tue, 1 Mar 2016 17:15:10 -0500 (EST) Received: by mail-pf0-f179.google.com with SMTP id 4so42121257pfd.1 for ; Tue, 01 Mar 2016 14:15:10 -0800 (PST) Received: from userp1040.oracle.com (userp1040.oracle.com. [156.151.31.81]) by mx.google.com with ESMTPS id kx15si14565499pab.43.2016.03.01.14.15.08 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 01 Mar 2016 14:15:10 -0800 (PST) Subject: Re: [Lsf-pc] [LSF/MM TOPIC] Support for 1GB THP References: <20160301070911.GD3730@linux.intel.com> <20160301102541.GD27666@quack.suse.cz> <20160301214403.GJ3730@linux.intel.com> From: Mike Kravetz Message-ID: <56D61467.5000006@oracle.com> Date: Tue, 1 Mar 2016 14:15:03 -0800 MIME-Version: 1.0 In-Reply-To: <20160301214403.GJ3730@linux.intel.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox , Jan Kara Cc: lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org On 03/01/2016 01:44 PM, Matthew Wilcox wrote: > On Tue, Mar 01, 2016 at 11:25:41AM +0100, Jan Kara wrote: >> On Tue 01-03-16 02:09:11, Matthew Wilcox wrote: >>> There are a few issues around 1GB THP support that I've come up against >>> while working on DAX support that I think may be interesting to discuss >>> in person. >>> >>> - Do we want to add support for 1GB THP for anonymous pages? DAX support >>> is driving the initial 1GB THP support, but would anonymous VMAs also >>> benefit from 1GB support? I'm not volunteering to do this work, but >>> it might make an interesting conversation if we can identify some users >>> who think performance would be better if they had 1GB THP support. >> >> Some time ago I was thinking about 1GB THP and I was wondering: What is the >> motivation for 1GB pages for persistent memory? Is it the savings in memory >> used for page tables? Or is it about the cost of fault? > > I think it's both. I heard from one customer who calculated that with > a 6TB server, mapping every page into a process would take ~24MB of > page tables. Multiply that by the 50,000 processes they expect to run > on a server of that size consumes 1.2TB of DRAM. Using 1GB pages reduces > that by a factor of 512, down to 2GB. > > Another topic to consider then would be generalising the page table > sharing code that is currently specific to hugetlbfs. I didn't bring > it up as I haven't researched it in any detail, and don't know how hard > it would be. Well, I have started down that path and have it working for some very simple cases with some very hacked up code. Too early/ugly to share. I'm struggling a bit with fact that you can have both regular and huge page mappings of the same regions. The hugetlb code only has to deal with huge pages. -- Mike Kravetz -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org