From: Mike Kravetz <mike.kravetz@oracle.com>
To: Matthew Wilcox <willy@linux.intel.com>, Jan Kara <jack@suse.cz>
Cc: lsf-pc@lists.linux-foundation.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org
Subject: Re: [Lsf-pc] [LSF/MM TOPIC] Support for 1GB THP
Date: Tue, 1 Mar 2016 14:15:03 -0800 [thread overview]
Message-ID: <56D61467.5000006@oracle.com> (raw)
In-Reply-To: <20160301214403.GJ3730@linux.intel.com>
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
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next prev parent reply other threads:[~2016-03-01 22:15 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-01 7:09 [LSF/MM TOPIC] Support for 1GB THP Matthew Wilcox
2016-03-01 10:25 ` [Lsf-pc] " Jan Kara
2016-03-01 11:00 ` Mel Gorman
2016-03-01 11:51 ` Mel Gorman
2016-03-01 12:09 ` Kirill A. Shutemov
2016-03-01 12:52 ` Mel Gorman
2016-03-01 21:44 ` Matthew Wilcox
2016-03-01 22:15 ` Mike Kravetz [this message]
2016-03-01 22:33 ` Rik van Riel
2016-03-01 22:36 ` James Bottomley
2016-03-02 14:14 ` Matthew Wilcox
2016-03-01 12:20 ` Kirill A. Shutemov
2016-03-01 16:32 ` Christoph Lameter
2016-03-01 21:47 ` Matthew Wilcox
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