Re: [PATCH v3 0/5] Introduce MADV_COLD and MADV_PAGEOUT

[Minchan Kim <minchan@kernel.org>]

On Thu, Jun 27, 2019 at 09:06:01PM +0300, Kirill A. Shutemov wrote:
> 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?

It was 100. Even, I tried 150 and 200 with simple hack of swappiness.
However, it caused too excessive swpout.

Anyway, systen-level tune is generally good but if process has hint, that
should work better and that's why advise API is.