kmap

OpenBSD uvm_mapent_alloc: out of static map entries

Submitted by tomo on April 2, 2011 - 3:02am

Every few months, I've had remote OpenBSD servers die mysteriously, without any visible console messages, and still responding to pings, although higher level networking (http, ssh) are unresponsive. The crontab I setup to dump output from top (or systat) also stops. But before the kernel failure load was low and swap was unused.

After rebooting and checking dmesg, I see before the most recent reboot:

uvm_mapent_alloc: out of static map entries

Doing some research, it seems like it could be a problem with kmem_map fragmentation, possibly from long-running processes (like apache, which is being used more heavily now). The problem appears to have been fixed in recent releases of OpenBSD which dynamically increase kmem, but upgrading the server right now isn't feasible.

So the solution is to compile a custom kernel with an increased MAX_KMAPENT added to GENERIC config:

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Asian-American expat living in Vietnam over 3 years. I am involved in tech startups and do Drupal consulting. I choose to live in Saigon and Vietnam and I want to see the city and its people reach their true potential.

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After the Vietnam/American War ended in 1975, many place names ceased to exist such as Saigon, South Vietnam, and plenty of street names.

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Those who haven't seen Vietnam for decades will be confused not just by the geographical changes but the incredible amount of development and modernization that has since taken place.

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