Description

The following article explains the log message " Approaching the limit on PV entries" on Juniper Networks devices.

Symptoms

The following is being logged in the messages file log:

Dec 5 09:29:22 Switch: Approaching the limit on PV entries, consider increasing either the vm.pmap.shpgperproc or the vm.pmap.pv_entry_max tunable.
Dec 5 09:34:23 Switch: Approaching the limit on PV entries, consider increasing either the vm.pmap.shpgperproc or the vm.pmap.pv_entry_max tunable.
Dec 5 09:37:34 Switch: Approaching the limit on PV entries, consider increasing either the vm.pmap.shpgperproc or the vm.pmap.pv_entry_max tunable.
Dec 5 09:38:36 Switch: Approaching the limit on PV entries, consider increasing either the vm.pmap.shpgperproc or the vm.pmap.pv_entry_max tunable.
Dec 5 09:39:58 Switch: Approaching the limit on PV entries, consider increasing either the vm.pmap.shpgperproc or the vm.pmap.pv_entry_max tunable.
Dec 5 09:41:55 Switch: Approaching the limit on PV entries, consider increasing either the vm.pmap.shpgperproc or the vm.pmap.pv_entry_max tunable.

Solution

On the kernel, each virtual address which is mapped to a given dynamically-allocated physical memory page uses up one pv_entry in the kernel, which contains information about that specific virtual translation. The kernel imposes a max limit on the number of pv entries that can be allocated on the system.

This message means the system is running low on pv entries in the kernel, and the kernel has detected this situation and initiates a pv entry reaping operation. The message is rate-limited using a simple time-based rate-limit checking that causes it to get printed certain amount of times over a given time interval. Then the kernel does not wait until the pool of pv entries has been completely exhausted before it takes actions to free up pv entries.

This ensures that no functional errors occur as result of the router running low on pv entries.

The log is harmless and informational in nature.

This can also be filtered out by following: How to Filter Two or More Specific Messages from being Written to the Syslog File.

Modification History

2023-03-15 KB created.