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Huge Shmem And PageTables Usage on Oracle Database Cluster Node When Database Has Performance Issue (Doc ID 2585510.1)

Last updated on SEPTEMBER 19, 2019

Applies to:

Linux OS - Version Oracle Linux 6.0 and later
Linux x86-64
Linux x86

Symptoms

The Oracle database (DB) cluster hangs up and has a performance issue during the period. DB slowness and Oracle DB access issue can be witnessed.
The Shmem And PageTables keep consistently high usage in OSwatcher's meminfo log. The MemFree is low.
The issue sometimes can be self-resolved. In the case, the Shmem And PageTables are reclaimed by itself.

 

OSwatcher meminfo log example for the issue period:

MemTotal: 264082720 kB <<< Total memory 252 GB
MemFree: 1050832 kB <<< Free 1 G
Buffers: 7720 kB
Cached: 99340708 kB
SwapCached: 1356728 kB
Active: 134084340 kB
Inactive: 3945440 kB
Active(anon): 133978132 kB
Inactive(anon): 3864228 kB
Active(file): 106208 kB
Inactive(file): 81212 kB
Unevictable: 715704 kB
Mlocked: 715704 kB
SwapTotal: 25165820 kB
SwapFree: 3619440 kB <<< Swap in use
Dirty: 120 kB
Writeback: 0 kB
AnonPages: 38105832 kB
Mapped: 98728744 kB
Shmem: 99052164 kB <<< Shmem 94 GB
Slab: 2518280 kB
SReclaimable: 1339016 kB
SUnreclaim: 1179264 kB
KernelStack: 56504 kB
PageTables: 84336732 kB <<< PageTables 80 GB
NFS_Unstable: 0 kB
Bounce: 0 kB
WritebackTmp: 0 kB
CommitLimit: 143557260 kB
Committed_AS: 234606864 kB
VmallocTotal: 34359738367 kB
VmallocUsed: 1178668 kB
VmallocChunk: 34224273668 kB
HardwareCorrupted: 0 kB
HugePages_Total: 13330
HugePages_Free: 3290 <<< Hugepage enabled, 3290 free
HugePages_Rsvd: 3278
HugePages_Surp: 0
Hugepagesize: 2048 kB
DirectMap4k: 8192 kB
DirectMap2M: 2023424 kB
DirectMap1G: 266338304 kB
 

The Linux system log may not report any error or warning in the issue period.

 

The hugepage memory has been configured and enabled. For example:

--meminfo
MemTotal: 264082720 kB
SwapTotal: 25165820 kB
AnonPages: 33372248 kB
PageTables: 58466416 kB
HugePages_Total: 13330
>>> Hugepage 10.34% of total memory

Cause

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In this Document
Symptoms
Cause
Solution
References


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