-XX:+PrintHeapAtGC
每次一次GC后，都打印堆信息
{Heap before GC invocations=0 (full 0):
def new generation total 3072K, used 2752K [0x33c80000, 0x33fd0000, 0x33fd0000)
eden space 2752K, 100% used [0x33c80000, 0x33f30000, 0x33f30000)
from space 320K, 0% used [0x33f30000, 0x33f30000, 0x33f80000)
to space 320K, 0% used [0x33f80000, 0x33f80000, 0x33fd0000)
tenured generation total 6848K, used 0K [0x33fd0000, 0x34680000, 0x34680000)
the space 6848K, 0% used [0x33fd0000, 0x33fd0000, 0x33fd0200, 0x34680000)
compacting perm gen total 12288K, used 143K [0x34680000, 0x35280000, 0x38680000)
the space 12288K, 1% used [0x34680000, 0x346a3c58, 0x346a3e00, 0x35280000)
ro space 10240K, 44% used [0x38680000, 0x38af73f0, 0x38af7400, 0x39080000)
rw space 12288K, 52% used [0x39080000, 0x396cdd28, 0x396cde00, 0x39c80000)
[GC[DefNew: 2752K->320K(3072K), 0.0014296 secs] 2752K->377K(9920K), 0.0014604 secs] [Times: user=0.00 sys=0.00, real=0.00 secs]
Heap after GC invocations=1 (full 0):
def new generation total 3072K, used 320K [0x33c80000, 0x33fd0000, 0x33fd0000)
eden space 2752K, 0% used [0x33c80000, 0x33c80000, 0x33f30000)
from space 320K, 100% used [0x33f80000, 0x33fd0000, 0x33fd0000)
to space 320K, 0% used [0x33f30000, 0x33f30000, 0x33f80000)
tenured generation total 6848K, used 57K [0x33fd0000, 0x34680000, 0x34680000)
the space 6848K, 0% used [0x33fd0000, 0x33fde458, 0x33fde600, 0x34680000)
compacting perm gen total 12288K, used 143K [0x34680000, 0x35280000, 0x38680000)
the space 12288K, 1% used [0x34680000, 0x346a3c58, 0x346a3e00, 0x35280000)
ro space 10240K, 44% used [0x38680000, 0x38af73f0, 0x38af7400, 0x39080000)
rw space 12288K, 52% used [0x39080000, 0x396cdd28, 0x396cde00, 0x39c80000)
}