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0 pointscdown8y ago0 comments

One problem with relying on the OOM killer in general is that the OOM killer is only invoked in moments of extreme starvation of memory. We really have no ability currently in Linux (or basically any operating system using overcommit) to determine when we're truly "out of memory", so the main metric used is our success or failure to reclaim enough pages to meet new demands.

As for the analogy -- there are metrics you can use today to bat away grandma before she starts hoarding too much. We have metrics for how much grandma is putting in the house (memory.stat), at what rate we kick our own stuff out of the house just to appease grandma, but then we realise we removed stuff we actually need (memory.stat -> workingset_refault), and similar. Using this and Johannes' recent work on memdelay (see https://patchwork.kernel.org/patch/10027103/ for some recent discussion), it's possible to see memory pressure before it actually impacts the system and drives things into swap.

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tmyklebu8y ago

> One problem with relying on the OOM killer in general is that the OOM killer is only invoked in moments of extreme starvation of memory. We really have no ability currently in Linux (or basically any operating system using overcommit) to determine when we're truly "out of memory", so the main metric used is our success or failure to reclaim enough pages to meet new demands.

The problem with relying on swap instead of the OOM killer is that, instead of the OOM killer, the user gets invoked in moments of extreme starvation of memory and the whole machine gets rebooted. The OOM killer is far gentler; it only kills processes until the extreme starvation is resolved.

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tmyklebu8y ago

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