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RHEL6.4(kernel 2.6.32-303)以降の vm.swappiness=0 と OOM Killer の関係

RHEL6.4(kernel 2.6.32-303)以降、vm.swappiness=0 にすると OOM Killer が発動しやすくなるので、1 にしましょうという話を見かけるのでメモ。詳しくは後日調べる予定。

Warning: Since Red Hat

Enterprise Linux 6.4, setting swappiness to 0 will even more aggressively avoid swapping out, which increases the risk of out-of-memory (OOM) killing under strong memory and I/O pressure. To achieve the same behavior of swappiness as previous versions of Red Hat Enterprise Linux 6.4 in which the recommendation was to set swappiness to 0, set swappiness to the value of 1. The recommendation of swappiness for Red Hat Enterprise Linux 6.4 or higher running Oracle databases is now the value of 1.

This obviously changed the way we think about “vm.swappiness=0”. Previously, setting this to 0 was thought to reduce the tendency to swap userland processes but not disable that completely. As such it was expected to see little swapping instead of OOM.

This applies to all RHEL/CentOS kernels > 2.6.32-303 and to other distributions that provide newer kernels such as Debian and Ubuntu. Or any other distribution where this change has been backported as in RHEL.