[BUG] Page allocation failures hitting servers where processes are memory hungry

Page allocation failures hitting servers where processes are memory hungry

Issue:

The kernel on RHEL 6 machines has a different behaviour compared with RHEL 5, with regards to page allocations. Many applications fail with page allocation errors when the machine has 90% or more of its memory used for filesystem cache. Traditionally in RHEL 5, the allocations would reclaim memory previously used for cache data.

Environment:

• Red Hat Enterprise Linux 6

Resolution:

A fix is being developed (tracked in Bugzilla 713546). A workaround also exists:

Workaround:

• Increase vm.min_free_kbytes kernel tunable to a higher value than a single allocation request.
• Change vm.zone_reclaim_mode to 1

Root Cause:

It seems that the system fails any page allocations, if the single allocation request is higher than the min_free_kbytes kernel tunable.

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