Disk I/O is still a big consumer of lowmem.

"Luck, Tony" [off-list ref] wrote:

quoted

If any significant percentage of memory is in ZONE_MOVABLE then the

memory

quoted

hotplug people will have to deal with all the lowmem/highmem problems
that used to be faced by 32-bit x86 with PAE enabled. 

While these problems may still exist on large systems - I think it
becomes
harder to construct workloads that run into problems.  In those bad old
days
a significant fraction of lowmem was consumed by the kernel ... so it
was
pretty easy to find meta-data intensive workloads that would push it
over
a cliff.  Here we  are talking about systems with say 128GB per node
divided
into 64GB moveable and 64GB non-moveable (and I'd regard this as a
rather
low-end machine).  Unless the workload consists of zillions of tiny
processes
all mapping shared memory blocks, the percentage of memory allocated to
the kernel is going to be tiny compared with the old 4GB days.

-Tony

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