Re: [RFC][-mm][PATCH 3/6] oom-killer: count lowmem rss

From: David Rientjes
Date: Tue Nov 03 2009 - 15:24:16 EST

On Mon, 2 Nov 2009, KAMEZAWA Hiroyuki wrote:

> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
> Count lowmem rss per mm_struct. Lowmem here means...
> for NUMA, pages in a zone < policy_zone.
> for HIGHMEM x86, pages in NORMAL zone.
> for others, all pages are lowmem.
> Now, lower_zone_protection[] works very well for protecting lowmem but
> possiblity of lowmem-oom is not 0 even if under good protection in the kernel.
> (As fact, it's can be configured by sysctl. When we keep it high, there
> will be tons of not-for-use memory but system will be protected against
> rare event of lowmem-oom.)

Right, lowmem isn't addressed currently by the oom killer. Adding this
constraint will probably make the heuristics much harder to write and
understand. It's not always clear that we want to kill a task using
lowmem just because another task needs some, for instance. Do you think
we'll need a way to defer killing any task is no task is heuristically
found to be hogging lowmem?
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