Re: [PATCH mm v3 3/3] mm: automatically penalize tasks with high swap use

On Sun, 17 May 2020 06:44:52 -0700 Shakeel Butt wrote:

quoted

Use one counter for number of pages allocated under pressure
to save struct task space and avoid two separate hierarchy
walks on the hot path.

The above para seems out of place. It took some time to realize you
are talking about current->memcg_nr_pages_over_high. IMO instead of
this para, a comment in code would be much better.

Where would you like to see the comment? In struct task or where
counter is bumped?

quoted

Take the new high limit into account when determining if swap
is "full". Borrowing the explanation from Johannes:

  The idea behind "swap full" is that as long as the workload has plenty
  of swap space available and it's not changing its memory contents, it
  makes sense to generously hold on to copies of data in the swap
  device, even after the swapin. A later reclaim cycle can drop the page
  without any IO. Trading disk space for IO.

  But the only two ways to reclaim a swap slot is when they're faulted
  in and the references go away, or by scanning the virtual address space
  like swapoff does - which is very expensive (one could argue it's too
  expensive even for swapoff, it's often more practical to just reboot).

  So at some point in the fill level, we have to start freeing up swap
  slots on fault/swapin.  

swap.high allows the user to force the kernel to start freeing swap
slots before half-full heuristic, right?

I'd say that the definition of full is extended to include swap.high.