On Thu, Jun 27, 2019 at 08:54:00PM +0900, Minchan Kim wrote:

- Problem

Naturally, cached apps were dominant consumers of memory on the system.
However, they were not significant consumers of swap even though they are
good candidate for swap. Under investigation, swapping out only begins
once the low zone watermark is hit and kswapd wakes up, but the overall
allocation rate in the system might trip lmkd thresholds and cause a cached
process to be killed(we measured performance swapping out vs. zapping the
memory by killing a process. Unsurprisingly, zapping is 10x times faster
even though we use zram which is much faster than real storage) so kill
from lmkd will often satisfy the high zone watermark, resulting in very
few pages actually being moved to swap.

Maybe we should look if we do The Right Thing™ at system-wide level before
introducing new API? How changing swappiness affects your workloads? What
is swappiness value in your setup?

-- 
 Kirill A. Shutemov