Re: [Lsf-pc] [LSF/MM TOPIC] Reclaim in the face of really fast I/O

[Sasha Levin <sasha.levin@oracle.com>]

On 01/15/2015 04:00 PM, Dave Hansen wrote:
> I/O devices are only getting faster.  In fact, they're getting closer
> and closer to memory in latency and bandwidth.  But the VM is still
> designed to do very orderly and costly procedures to reclaim memory, and
> the existing algorithms don't parallelize particularly well.  They hit
> contention on mmap_sem or the lru locks well before all of the CPU
> horsepower that we have can be brought to bear on reclaim.
> 
> Once the latency to bring pages in and out of storage becomes low
> enough, reclaiming the _right_ pages becomes much less important than
> doing something useful with the CPU horsepower that we have.
> 
> We need to talk about ways to do reclaim with lower CPU overhead and to
> parallelize more effectively.
> 
> There has been some research in this area by some folks at Intel and we
> could quickly summarize what has been learned so far to help kick off a
> discussion.

I was actually planning to bring that up. Trinity can cause enough stress
to a system that the hang watchdog triggers (with a 10 minute timeout!)
inside reclaim code.


Thanks,
Sasha

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