improve kmalloc performance

improve kmalloc performance

Reading from /proc/meminfo is really slow

We don't want to start swapping to disk.

Deceptively, memory available goes up when we start to swap to disk making
performance even worse.

To mitigate this:
1. replace reading from meminfo with proper system calls.
2. attempt to lock allocations in physical memory space.
3. check our own allocated memory instead of available memory.
4. still check available memory in the off chance we're trying to play
nice with other apps.

Signed-off-by: Daniel Hill <daniel@gluo.nz>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>