Hi Lucy, I am struggling to find an entirely satisfactory location to place a method such as getPageSize, but java.lang.Runtime seems less worse than other places :-)
Paul. > On 3 Nov 2016, at 12:49, Lu, Yingqi <yingqi...@intel.com> wrote: > > Hi Paul and Peter, > > Thank you very much for pointing this out. We did not know about it J > > We will modify the patch accordingly and will send it here for review. > > Thanks, > Lucy > > From: Paul Sandoz [mailto:paul.san...@oracle.com] > Sent: Thursday, November 03, 2016 12:46 PM > To: Peter Levart <peter.lev...@gmail.com> > Cc: Lu, Yingqi <yingqi...@intel.com>; Alan Bateman <alan.bate...@oracle.com>; > nio-...@openjdk.java.net; Kaczmarek, Eric <eric.kaczma...@intel.com>; > core-libs-dev@openjdk.java.net; Kharbas, Kishor <kishor.khar...@intel.com> > Subject: Re: Proposal for adding O_DIRECT support into JDK 9 > > Hi Peter, > > Thanks for pointing this out, you beat me to it :-) > > Note that the alignment for a unit size corresponding to page size will only > be stable for direct byte buffers, since for heap byte buffers the GC can > move the underlying byte array and the alignment properties may change. > > Paul. > > On 3 Nov 2016, at 12:38, Peter Levart <peter.lev...@gmail.com> wrote: > > Hi Lucy, > > Did you know that in JDK 9 the following two methods have been added to > java.nio.ByteBuffer: > > /** @return The indexed byte's memory address modulus the unit size > */ > public final int alignmentOffset(int index, int unitSize); > > /** @return new byte buffer whose content is a shared and aligned subsequence > of this buffer's content > */ > public final ByteBuffer alignedSlice(int unitSize); > > > So you could express your proposed methods ByteBuffer.allocateDirectAligned() > and ByteBuffer.isAligned() with the above two methods in the following way: > > instead of: > > ByteBuffer bb = ByteBuffer.allocateDirectAligned(capacity) > > you could do: > > int pageSize = ... > ByteBuffer bb = ByteBuffer.allocateDirect(capacity + pageSize - > 1).alignedSlice(pageSize); > > And instead of: > > bb.isAligned() > > you could do: > > bb.alignmentOffset(pageSize) == 0 > > > > The only thing that needs to be added is a public API to return the pageSize > (i.e. Bits.pageSize()). > > > What do you think? > > Regards, Peter > > On 11/03/2016 12:34 AM, 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.
