On Thu, Feb 4, 2016 at 8:02 PM, Jon Masamitsu <jon.masami...@oracle.com> wrote:
> > > On 02/04/2016 06:41 AM, Thomas Stüfe wrote: > > Hi Timur, > > I believe you see the space for the compressed class data (Compressed > class space), which is by default 1GB and controlled by > -XX:CompressedClassSpaceSize . I think this area is semantically one > subarea of the metaspace, the other being non-class data. > > I am unsure about the difference between MaxMetaSpaceSize and > CompressedClassSpaceSize, but what I believe is that: > > - MaxMetaSpaceSize limits the amount of total committed (not reserved) > space > - CompressedClassSpaceSize sets the amount of space to be reserved (not > committed) for compressed classes only. > > This would fit your NMT output, which says: > > "Class (reserved=1142808KB, committed=106520KB)" > > so, ~100M are committed. With a MaxMetaSpaceSize=256M - what you specified > - you would not be able to commit the whole 1GB, but hit the limit far > earlier. > > See also: > https://docs.oracle.com/javase/8/docs/technotes/guides/vm/gctuning/considerations.htm > (the section about UseCompressedClassesPointers) > > Please take this with a grain of salt. I am not sure I understand this > correctly and would value input from other developers. > > > Thomas, > > No disagreement from me. I think you described it > correctly. Note that if you turn off UseCompressedClassPointers, > there will not be a separate space for the class metadata. > > Jon > > Jon, thanks for confirming! ..Thomas > > > Kind Regards, Thomas > > On Thu, Feb 4, 2016 at 2:13 PM, Timur Akhmadeev <timur.akhmad...@gmail.com > > wrote: > >> Hi, >> >> I'm trying to figure out which parts of memory Hotspot can allocate in >> HugePages on Linux (appears to be heap and code cache by default, plus >> Metaspace with -XX:+UseLargePagesInMetaspace) and noticed something I can't >> explain. >> >> There's 1G allocation on the OS level in 4K pages that is apparently >> attributed to Class metadata, although Metaspace is maxed at a value much >> lower than 1G. Question: why? >> >> [oracle@oel6u7 bin]$ grep -B 11 'KernelPageSize: 4 kB' >> /proc/18906/smaps | grep '^Size:' | head >> Size: 4 kB >> Size: 4 kB >> Size: 2764 kB >> Size: 12288 kB >> Size: 1036288 kB >> Size: 128 kB >> Size: 4 kB >> Size: 4 kB >> Size: 4 kB >> Size: 8 kB >> >> [oracle@oel6u7 bin]$ /home/oracle/jdk1.8.0_72/bin/jcmd 18906 >> VM.native_memory summary >> 18906: >> >> Native Memory Tracking: >> >> Total: reserved=2069703KB, committed=1032559KB >> - Java Heap (reserved=786432KB, committed=786432KB) >> (mmap: reserved=786432KB, committed=786432KB) >> >> - Class (reserved=1142808KB, committed=106520KB) >> (classes #13624) >> (malloc=2072KB #22966) >> (mmap: reserved=1140736KB, >> committed=104448KB) >> >> - Thread (reserved=56009KB, committed=56009KB) >> (thread #55) >> (stack: reserved=55512KB, committed=55512KB) >> (malloc=178KB #272) >> (arena=319KB #108) >> >> - Code (reserved=55407KB, committed=55407KB) >> (malloc=5487KB #7167) >> (mmap: reserved=49920KB, committed=49920KB) >> >> - GC (reserved=2600KB, committed=1748KB) >> (malloc=32KB #355) >> (mmap: reserved=2568KB, committed=1716KB) >> >> - Compiler (reserved=213KB, committed=213KB) >> (malloc=82KB #331) >> (arena=131KB #3) >> >> - Internal (reserved=4921KB, committed=4917KB) >> (malloc=4885KB #16137) >> (mmap: reserved=36KB, committed=32KB) >> >> - Symbol (reserved=17518KB, committed=17518KB) >> (malloc=14377KB #172159) >> (arena=3141KB #1) >> >> - Native Memory Tracking (reserved=3617KB, committed=3617KB) >> (malloc=149KB #2329) >> (tracking overhead=3468KB) >> >> - Arena Chunk (reserved=178KB, committed=178KB) >> (malloc=178KB) >> >> [oracle@oel6u7 bin]$ /home/oracle/jdk1.8.0_72/bin/jcmd 18906 >> VM.native_memory detail | grep -A 10 'for Class' >> [0x0000000100000000 - 0x0000000140000000] reserved 1048576KB for Class >> from >> [0x00007f71950e2ad2] ReservedSpace::initialize(unsigned long, >> unsigned long, bool, char*, unsigned long, bool)+0xc2 >> [0x00007f71950e2d0b] ReservedSpace::ReservedSpace(unsigned long, >> unsigned long, bool, char*, unsigned long)+0x1b >> [0x00007f7194ec8300] >> Metaspace::allocate_metaspace_compressed_klass_ptrs(char*, unsigned >> char*)+0x40 >> [0x00007f7194eca7df] Metaspace::global_initialize()+0x4cf >> >> [0x0000000100000000 - 0x0000000100c00000] committed 12288KB from >> [0x00007f71950e2549] VirtualSpace::expand_by(unsigned long, >> bool)+0x199 >> [0x00007f7194ec6766] >> VirtualSpaceList::expand_node_by(VirtualSpaceNode*, unsigned long, unsigned >> long)+0x76 >> [0x00007f7194ec9580] VirtualSpaceList::expand_by(unsigned >> long, unsigned long)+0xf0 >> [0x00007f7194ec9713] VirtualSpaceList::get_new_chunk(unsigned >> long, unsigned long, unsigned long)+0xb3 >> ... >> >> [oracle@oel6u7 bin]$ head ../logs/gc.log >> Java HotSpot(TM) 64-Bit Server VM (25.72-b15) for linux-amd64 JRE >> (1.8.0_72-b15), built on Dec 22 2015 22:00:07 by "java_re" with gcc 4.3.0 >> 20080428 (Red Hat 4.3.0-8) >> Memory: 4k page, physical 3082784k(506980k free), swap 1257468k(1148276k >> free) >> CommandLine flags: -XX:InitialCodeCacheSize=50331648 >> -XX:InitialHeapSize=49324544 -XX:MaxHeapSize=805306368 >> -XX:MaxMetaspaceSize=268435456 -XX:MetaspaceSize=268435456 >> -XX:NativeMemoryTracking=detail -XX:+PrintGC -XX:+PrintGCTimeStamps >> -XX:ReservedCodeCacheSize=50331648 -XX:+UseCompressedClassPointers >> -XX:+UseCompressedOops -XX:+UseLargePages -XX:+UseLargePagesInMetaspace >> >> -- >> Regards >> Timur Akhmadeev >> >> _______________________________________________ >> hotspot-gc-use mailing list >> hotspot-gc-use@openjdk.java.net >> http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use >> >> > > > _______________________________________________ > hotspot-gc-use mailing > listhotspot-gc-...@openjdk.java.nethttp://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use > > > > _______________________________________________ > hotspot-gc-use mailing list > hotspot-gc-use@openjdk.java.net > http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use > >
_______________________________________________ hotspot-gc-use mailing list hotspot-gc-use@openjdk.java.net http://mail.openjdk.java.net/mailman/listinfo/hotspot-gc-use
