Hey Andrew,

On Tue, Jul 02, 2024 at 12:42:54AM -0700, Andrew Morton wrote:

The patch is impressively comment-free.  It is a little harsh to make
readers go poking around in the git history to figure out what
VM_DROPPABLE is, and why it exists.

Sure, I'll add some comments to the conditionals added to make it more
clear.

Seems hard to test that this mode is working correctly.  Can you think
of a way for userspace to check this?  And if so, add it to selftests?

I've got a pretty straight forward test I've been using during my own
testing that I can add to the vgetrandom_alloc() selftest (which exposes
these code paths). It works fairly reliably. Basically, one process
keeps checking to see if the memory has been dropped, while the other
consumes memory a page at a time. Pretty soon (depending on how much ram
you have), the memory gets dropped, and this is detected, and the test
completes with a pass. I'll have this in v+1 of this series.

Jason