[PATCH] mm: disable fault around on emulated access bit architecture

[Minchan Kim]

On Tue, May 17, 2016 at 03:34:23PM +0300, Kirill A. Shutemov wrote:
> On Mon, May 16, 2016 at 11:56:32PM +0900, Minchan Kim wrote:
> > On Mon, May 16, 2016 at 05:29:00PM +0300, Kirill A. Shutemov wrote:
> > > > Kirill,
> > > > You wanted to test non-HW access bit system and I did.
> > > > What's your opinion?
> > > 
> > > Sorry, for late response.
> > > 
> > > My patch is incomlete: we need to find a way to not mark pte as old if we
> > > handle page fault for the address the pte represents.
> > 
> > I'm sure you can handle it but my point is there wouldn't be a big gain
> > although you can handle it in non-HW access bit system. Okay, let's be
> > more clear because I don't have every non-HW access bit architecture.
> > At least, current mobile workload in ARM which I have wouldn't be huge
> > benefit.
> > I will say one more.
> > I tested the workload on quad-core system and core speed is not so slow
> > compared to recent other mobile phone SoC. Even when I tested the benchmark
> > without pte_mkold, the benefit is within noise because storage is really
> > slow so major fault is dominant factor. So, I decide test storage from eMMC
> > to eSATA. And then finally, I manage to see the a little beneift with
> > fault_around without pte_mkold.
> > 
> > However, let's consider side-effect aspect from fault_around.
> > 
> > 1. Increase slab shrinking compard to old
> > 2. high level vmpressure compared to old
> > 
> > With considering that regressions on my system, it's really not worth to
> > try at the moment.
> > That's why I wanted to disable fault_around as default in non-HW access
> > bit system.
> 
> Feel free to post such patch. I guess it's reasonable.