mm: disable fault around on emulated access bit architecture

Quoted 25 lines · Minchan Kim

Quoted 8 lines · Kirill A. Shutemov

Quoted 3 lines

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.

Quoted 7 lines

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.