Re: [PATCH] mm/thp: don't count ZONE_MOVABLE as the target for freepage reserving

[Joonsoo Kim]

On Thu, Apr 05, 2018 at 05:05:39PM +0900, Joonsoo Kim wrote:
> On Thu, Apr 05, 2018 at 09:57:53AM +0200, Michal Hocko wrote:
> > On Thu 05-04-18 16:27:16, Joonsoo Kim wrote:
> > > From: Joonsoo Kim <iamjoonsoo.kim@xxxxxxx>
> > > 
> > > ZONE_MOVABLE only has movable pages so we don't need to keep enough
> > > freepages to avoid or deal with fragmentation. So, don't count it.
> > > 
> > > This changes min_free_kbytes and thus min_watermark greatly
> > > if ZONE_MOVABLE is used. It will make the user uses more memory.

Oops.. s/more/less

> > 
> > OK, but why does it matter. Has anybody seen this as an issue?
> 
> There was a regression report for CMA patchset and I think that it is
> related to this problem. CMA patchset makes the system uses one more
> zone (ZONE_MOVABLE) and then increase min_free_kbytes. It reduces
> usable memory and it could cause regression.
> 
> http://lkml.kernel.org/r/20180102063528.GG30397@yexl-desktop

Thanks.