I have 64-bit Linux machine(Intel Xeon L5410 @ 2.33GHz).
**meminfo:**
MemTotal: 24672736 kB
MemFree: 145372 kB
Buffers: 181896 kB
Cached: 22004648 kB
SwapCached: 195072 kB
Active: 9761028 kB
Inactive: 13964532 kB
HighTotal: 0 kB
HighFree: 0 kB
LowTotal: 24672736 kB
LowFree: 145372 kB
SwapTotal: 17414452 kB
SwapFree: 15618852 kB
Dirty: 2125148 kB
Writeback: 0 kB
AnonPages: 1358396 kB
Mapped: 1069632 kB
Slab: 699464 kB
CommitLimit: 29750820 kB
Committed_AS: 9236252 kB
PageTables: 38620 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 17272 kB
VmallocChunk: 34359718843 kB
HugePages_Total: 0
HugePages_Free: 0
HugePages_Rsvd: 0
Hugepagesize: 2048 kB
**Also the shm details are:**
shmall 2097152
shmmax 3294967296
shmmni 4096
I am trying to create shared memory above 2 GB, shmget is successful but later core dump occurs with the error that cannot access memory. While shared memory below 2GB works perfectly fine. I am able to find any valid reason for this as my shmmax value is around 3GB
the maximum shm memory size is available thru /proc/sys/kernel/shmmax and you could write into that pseudo-file to change it. It probably cannot be raised above some portion (e.g. half) of physical RAM. Perhaps some kernel configuration can change that.
You can also share memory with the mmap syscall with MAP_SHARED flag.
来源：https://stackoverflow.com/questions/10991111/max-possible-shared-memory-size-in-64-bit-linux-machine