How to minimize (unshareable) memory usage?

[Justin Santa Barbara <justin at fathomdb dot com>]

I have some simple Java utilities that I've written that need to run
on machines with limited free memory, and I'm looking at GCJ for this.
 Using the full Sun JVM we run into problems with memory usage - we're
able to limit the heap to 8MB, but we need to allow at least 16MB for
PermGen (despite not really having much application code), and at
least 8MB for ReservedCodeCacheSize;? even a simple utility therefore
needs at least 32MB of unshareable memory.

Running under GCJ the results are encouraging, but still not as good
as I'd hope.? The output from pmap is included below.? The interesting
ones are these four:
00010000? 10404K rw---??? [ anon ]
b4125000?? 8192K rw---??? [ anon ]
b49d2000?? 8192K rw---??? [ anon ]
b7096000?? 6324K rw---? /usr/lib/libgcj.so.10.0.0

I've limited GCJ to 10MB of heap (it seems to need a little more than
the Sun JVM for some reason), so that's the first entry.? But what are
the two 8MB anonymous allocations that aren't the 10MB heap?   What is
the 6MB of read/write libgcj mappings?

Any hints on how to minimize unshareable memory usage would be greatly
appreciated.

I'm using the default gcj from Ubuntu Karmic (gcj -v output also included below)

Thanks,
Justin


00010000? 10404K rw---??? [ anon ]
08048000??? 244K r-x--? /tmp/a.out
08085000???? 56K rw---? /tmp/a.out
08093000???? 12K rw---??? [ anon ]
09719000??? 404K rw---??? [ anon ]
b4124000????? 4K -----??? [ anon ]
b4125000?? 8192K rw---??? [ anon ]
b4925000???? 64K r-x--? /lib/tls/i686/cmov/libresolv-2.10.1.so
b4935000????? 4K r----? /lib/tls/i686/cmov/libresolv-2.10.1.so
b4936000????? 4K rw---? /lib/tls/i686/cmov/libresolv-2.10.1.so
b4937000????? 8K rw---??? [ anon ]
b4939000???? 20K r-x--? /lib/tls/i686/cmov/libnss_dns-2.10.1.so
b493e000????? 4K r----? /lib/tls/i686/cmov/libnss_dns-2.10.1.so
b493f000????? 4K rw---? /lib/tls/i686/cmov/libnss_dns-2.10.1.so
b4940000??? 380K r-x--? /usr/lib/libgmp.so.3.5.0
b499f000????? 4K r----? /usr/lib/libgmp.so.3.5.0
b49a0000????? 4K rw---? /usr/lib/libgmp.so.3.5.0
b49bc000???? 84K r----? /var/lib/gcj-4.4/classmap.db
b49d1000????? 4K -----??? [ anon ]
b49d2000?? 8192K rw---??? [ anon ]
b51d2000??? 948K r----? /usr/lib/locale/en_US.utf8/LC_COLLATE
b52bf000???? 40K r-x--? /lib/tls/i686/cmov/libnss_files-2.10.1.so
b52c9000????? 4K r----? /lib/tls/i686/cmov/libnss_files-2.10.1.so
b52ca000????? 4K rw---? /lib/tls/i686/cmov/libnss_files-2.10.1.so
b52cb000???? 76K r-x--? /lib/tls/i686/cmov/libnsl-2.10.1.so
b52de000????? 4K r----? /lib/tls/i686/cmov/libnsl-2.10.1.so
b52df000????? 4K rw---? /lib/tls/i686/cmov/libnsl-2.10.1.so
b52e0000????? 8K rw---??? [ anon ]
b52e4000????? 8K r-x--? /lib/libnss_mdns4.so.2
b52e6000????? 4K r----? /lib/libnss_mdns4.so.2
b52e7000????? 4K rw---? /lib/libnss_mdns4.so.2
b52e8000????? 8K r-x--? /lib/libnss_mdns4_minimal.so.2
b52ea000????? 4K r----? /lib/libnss_mdns4_minimal.so.2
b52eb000????? 4K rw---? /lib/libnss_mdns4_minimal.so.2
b52ec000???? 20K r-x--? /usr/lib/gcj-4.4-10/libjavamath.so
b52f1000????? 4K rw---? /usr/lib/gcj-4.4-10/libjavamath.so
b52f2000????? 4K rw-s-? /tmp/ffiTjScy8 (deleted)
b52f3000????? 4K r-xs-? /tmp/ffiTjScy8 (deleted)
b52f4000????? 4K r----? /usr/lib/locale/en_US.utf8/LC_NUMERIC
b52f5000????? 4K r----? /usr/lib/locale/en_US.utf8/LC_TIME
b52f6000????? 4K r----? /usr/lib/locale/en_US.utf8/LC_MONETARY
b52f7000????? 4K r----? /usr/lib/locale/en_US.utf8/LC_MESSAGES/SYS_LC_MESSAGES
b52f8000????? 4K r----? /usr/lib/locale/en_US.utf8/LC_PAPER
b52f9000????? 4K r----? /usr/lib/locale/en_US.utf8/LC_NAME
b52fa000????? 4K r----? /usr/lib/locale/en_US.utf8/LC_ADDRESS
b52fb000????? 4K r----? /usr/lib/locale/en_US.utf8/LC_TELEPHONE
b52fc000????? 4K r----? /usr/lib/locale/en_US.utf8/LC_MEASUREMENT
b52fd000??? 252K r----? /usr/lib/locale/en_US.utf8/LC_CTYPE
b533c000????? 8K rw---??? [ anon ]
b533e000?? 1272K r-x--? /lib/tls/i686/cmov/libc-2.10.1.so
b547c000????? 8K r----? /lib/tls/i686/cmov/libc-2.10.1.so
b547e000????? 4K rw---? /lib/tls/i686/cmov/libc-2.10.1.so
b547f000???? 12K rw---??? [ anon ]
b5482000????? 8K r-x--? /lib/tls/i686/cmov/libdl-2.10.1.so
b5484000????? 4K r----? /lib/tls/i686/cmov/libdl-2.10.1.so
b5485000????? 4K rw---? /lib/tls/i686/cmov/libdl-2.10.1.so
b5486000???? 80K r-x--? /lib/libz.so.1.2.3.3
b549a000????? 4K r----? /lib/libz.so.1.2.3.3
b549b000????? 4K rw---? /lib/libz.so.1.2.3.3
b549c000???? 28K r-x--? /lib/tls/i686/cmov/librt-2.10.1.so
b54a3000????? 4K r----? /lib/tls/i686/cmov/librt-2.10.1.so
b54a4000????? 4K rw---? /lib/tls/i686/cmov/librt-2.10.1.so
b54a5000???? 84K r-x--? /lib/tls/i686/cmov/libpthread-2.10.1.so
b54ba000????? 4K r----? /lib/tls/i686/cmov/libpthread-2.10.1.so
b54bb000????? 4K rw---? /lib/tls/i686/cmov/libpthread-2.10.1.so
b54bc000????? 8K rw---??? [ anon ]
b54be000??? 144K r-x--? /lib/tls/i686/cmov/libm-2.10.1.so
b54e2000????? 4K r----? /lib/tls/i686/cmov/libm-2.10.1.so
b54e3000????? 4K rw---? /lib/tls/i686/cmov/libm-2.10.1.so
b54e4000????? 4K rw---??? [ anon ]
b54e5000? 28356K r-x--? /usr/lib/libgcj.so.10.0.0
b7096000?? 6324K rw---? /usr/lib/libgcj.so.10.0.0
b76c3000??? 280K rw---??? [ anon ]
b7709000??? 112K r-x--? /lib/libgcc_s.so.1
b7725000????? 4K r----? /lib/libgcc_s.so.1
b7726000????? 4K rw---? /lib/libgcc_s.so.1
b7727000????? 4K r----? /usr/lib/locale/en_US.utf8/LC_IDENTIFICATION
b7728000???? 36K r-x--? /lib/tls/i686/cmov/libnss_nis-2.10.1.so
b7731000????? 4K r----? /lib/tls/i686/cmov/libnss_nis-2.10.1.so
b7732000????? 4K rw---? /lib/tls/i686/cmov/libnss_nis-2.10.1.so
b7733000???? 24K r-x--? /lib/tls/i686/cmov/libnss_compat-2.10.1.so
b7739000????? 4K r----? /lib/tls/i686/cmov/libnss_compat-2.10.1.so
b773a000????? 4K rw---? /lib/tls/i686/cmov/libnss_compat-2.10.1.so
b773b000???? 28K r--s-? /usr/lib/gconv/gconv-modules.cache
b7742000????? 8K rw---??? [ anon ]
b7744000????? 4K r-x--??? [ anon ]
b7745000??? 108K r-x--? /lib/ld-2.10.1.so
b7760000????? 4K r----? /lib/ld-2.10.1.so
b7761000????? 4K rw---? /lib/ld-2.10.1.so
bff3e000???? 84K rw---??? [ stack ]
?total??? 66632K



gcj -v
Using built-in specs.
Reading specs from /usr/lib/gcc/i486-linux-gnu/4.4.1/libgcj.spec
rename spec startfile to startfileorig
rename spec lib to liborig
Target: i486-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
4.4.1-5ubuntu2'
--with-bugurl=file:///usr/share/doc/gcj-4.4/README.Bugs
--enable-languages=c,c++,java --prefix=/usr --enable-shared
--enable-multiarch --enable-linker-build-id --with-system-zlib
--libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --with-gxx-include-dir=/usr/include/c++/4.4
--program-suffix=-4.4 --enable-nls --enable-clocale=gnu
--disable-libmudflap --enable-java-awt=gtk --enable-gtk-cairo
--disable-plugin --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-4.4/jre
--enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-4.4
--with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-4.4
--with-arch-directory=i386
--with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-targets=all
--disable-werror --with-arch-32=i486 --with-tune=generic
--enable-checking=release --build=i486-linux-gnu --host=i486-linux-gnu
--target=i486-linux-gnu
Thread model: posix
gcc version 4.4.1 (Ubuntu 4.4.1-5ubuntu2)