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## Problem Over the past couple days, we've had a couple VMs hit issues with postgres getting hit by memory.high throttling, even after #5303 was supposed to fix that. The tl;dr of those issues is that because vm-monitor startup sets the file cache size first, before interacting with the cgroup, cgroup throttling can mean we timeout connecting to the file cache and never reset the cgroup, even if memory has been upscaled since then. See e.g.: - https://neondb.slack.com/archives/C03F5SM1N02/p1695218132208249 - https://neondb.slack.com/archives/C03F5SM1N02/p1695314613696659 ## Summary of changes This PR adds an additional step into vm-monitor startup, where we first set the cgroup's memory.high value to 'max', removing the capacity for throttling. This preferable to just setting memory.high before the file cache, because it's theoretically possible that the new value of memory.high could still be less than the current memory usage, in which case postgres could continue to be throttled without sufficient memory events to relieve that. Implementing this properly involved adding a method to our internal cgroup interface, and it seemed like there was duplicated functionality there, so this PR unifies that as well, making things a bit more consistent.