>> > I suspect a big factor here is CONFIG_ARM64_64K_PAGES=y. Raspberry pi
>> > 3, with standard fedora kernel (64k pages), minimal install (@core),
>> > booted to the shell prompt. "free" reports ~122MB of memory as used.
>> > Same with a self-compiled kernel (4k pages), I get ~44MB of used memory.
>> > That is almost factor three!
>> That is almost the complete factor. It's in fact a combination of 64K
>> pages and CMA. The two together mean that the minimum CMA allocated is
>> 512Mb of RAM. It's a known problem and one we're looking at different
>> ways/options to resolve and working with upstream to do so and
>> reconsidering 64K pages in Fedora. We've traditionally gone that route
>> due to large enterprise systems and to be in sync with downstreams
>> like RHELSA and CentOS in that regard.
> What was the reason to go 64k pages in the first place? Sure, with
> larger pages memory management overhead goes down. But on the other
> hand the memory footprint goes up, and frankly I'm a bit surprised how
> much it goes up. So I'm wondering whenever 64k pages is a net win even
> on enterprise machines. Did people benchmark this?
TBH I'm not sure of all of the reasons, for some use cases like
hypervisors where the processes you have running (VMs) tend to have
large memory allocations I can see it's benefits.
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