What happens if you're using large pages? Are the direct buffers always
allocated off of small pages?
On 11/02/2016 06:34 PM, Lu, Yingqi wrote:
Hi All,
Our most recent DirectIO patch is available at
http://cr.openjdk.java.net/~igraves/8164900-3/
In this version, we made following changes:
1. Removed the flag "direct" from FileDescriptor class. Instead, moved it to
the FileChannelImpl class.
2. Provided a way for user to allocate a page aligned direct ByteBuffer.
1) Added a constructor DirectByteBuffer(int cap, boolean direct) to
allocate a direct ByteBuffer that is aligned to the page size.
2) Added Util.getTemporaryAlignedDirectBuffer(int size)
3) Added DirectByteBuffer.isAligned(int pos) to check if the buffer is
aligned before doing native IO with it.
3. Moved all the alignment check from C code to Java code (mainly
FileChannelImpl and IOUtil.java).
4. Made the DirectIO functionality consistent between read and write
operations. With current version of the patch, user would be responsible for
the alignment with file offset and IO size.
5. Made the API for DirectIO more extensible to all the supporting platforms.
1) Unix OS specific code are done through UnixConstants.java.template and
FileChannelImpl.c.
2) Coded and tested for Linux and OS X (OS X testing is done through
VirtualBox with OS X VM on top of Linux OS).
3) Coded for Solaris. We do not have environment to test it so that we
commented the changes out.
6. We added 4 test cases following the existing non-direct IO examples.
7. We did jtreg test for the entire nio package and no errors were found due to
our changes.
Please let us know your feedback and comment. Thank you very much for your time
and consideration!
Thanks,
Lucy
-----Original Message-----
From: Alan Bateman [mailto:alan.bate...@oracle.com]
Sent: Monday, October 17, 2016 7:59 AM
To: Lu, Yingqi <yingqi...@intel.com>
Cc: nio-...@openjdk.java.net; Kaczmarek, Eric <eric.kaczma...@intel.com>;
Kharbas, Kishor <kishor.khar...@intel.com>
Subject: Re: Proposal for adding O_DIRECT support into JDK 9
On 12/10/2016 17:41, Lu, Yingqi wrote:
:
You are correct about the "extra copy" with DirectIO. Will it be acceptable if
we
add a function "Util.getAlignedTemporaryDirectBuffer" and use that for the
DirectIO operation? In this case, I think we should be able to avoid the
additional
copy?
Yes, that should work but it still lacks a way for the user to get an aligned
buffer
and so you will always be copying in and out of an aligned buffer. The other
thing
is the sizing of the I/O operation where I think you will also need a way to
expose
the multiple (or block size) to the user.
-Alan.
--
- DML
