Why not call aligned_alloc for doing page alignment? It should waste much less memory.
http://en.cppreference.com/w/c/memory/aligned_alloc On Thu, Nov 3, 2016 at 8:14 AM, David M. Lloyd <david.ll...@redhat.com> wrote: > 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 >
