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There are some drawbacks to that. Memory flagged as hotplug can't be used by the kernel itself (because otherwise unplugging the RAM would risk crashing the sy

There are some drawbacks to that. Memory flagged as hotplug can't be used by the kernel itself (because otherwise unplugging the RAM would risk crashing the system). That includes things like network buffers and a number of things which use the total RAM size as a guideline. There was a bug in a proposed kernel patch a while back, that we were testing. It ended up designating a good chunk of the machine's RAM as hotpluggable. Test suite was passing, but the benchmarks showed a drastic performance drop. Took a while to track down why that was happening.

madez 7y ago
Isn't the solution introducing another type of memory abstraction in the kernel next to "available since boot" and "hot pluggable", namely "later added but won't be removed"?
- hansendc 7y ago
  This solution didn't introduce it. The concepts being used have existed in Linux for quite some time. Here's a patch of mine that added (some of) it from 2005: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3947be1969a9 https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/lin...
hansendc 7y ago
I think you may be confusing some of the aspects of hot-add with hot-remove. Memory which you want to later remove should be onlined as "movable" and it has some content limitations. But, not all hot-added memory must be onlined that way. You can very easily just online it as "normal", which is (believe it or not) normal and can have any allocation type placed there.