RE: OT - Blog entry on hugepages

Jed,

Your "one above" (the one with 268435456 bytes) and the one below (2097152 bytes) are all shared memory segments used by the same instance. The clue is the same number of attachments (very unlikely they all happen to have 59 processes) and the fact that two of them have all-zero keys. Your 51271172096/1024/1024/1024 is 47.75 GB and 268435456/1024/1024/1024 is 0.25 GB. It always seems to have an extra 2MB segment.

Here's what I have (on my 64-bit Red Hat Linux 6 sandbox, uncertified!):

$ ipcs -m

• Shared Memory Segments -------- key shmid owner perms bytes nattch status 0x00000000 229377 oracle 640 4096 0 0x00000000 262146 oracle 640 4096 0 0xb260fc88 294915 oracle 640 4096 0 0x00000000 1933316 oracle 640 16777216 57 0x00000000 1966085 oracle 640 1174405120 57 0xb82bfec8 1998854 oracle 640 2097152 57

$ ps -ef | grep pmon

oracle   11895     1  0 Apr05 ?        00:00:25 ora_pmon_sanora1
oracle   13195     1  0 Apr04 ?        00:00:31 asm_pmon_+ASM1

Now check the shared memory segments in the process memory map:

# egrep '1933316|1966085|1998854' /proc/11895/maps

60000000-61000000 rwxs 00000000 00:04 1933316                            /SYSV00000000 (deleted)
61000000-a7000000 rwxs 00000000 00:04 1966085                            /SYSV00000000 (deleted)
a7000000-a7200000 rwxs 00000000 00:04 1998854                            /SYSVb82bfec8 (deleted)

(My ASM is using /dev/shm so ignore that.) You see all the 3 so-called SystemV shared memory segments. And the sizes are

60000000-61000000 -> 16777216 bytes
61000000-a7000000 -> 1174405120 bytes 
a7000000-a7200000 -> 2097152 bytes

The above check can be done regardless HugePages usage. In fact, my Oracle on Red Hat 6 was just installed and I haven't configured HugePages yet.

Yong Huang

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