Re: [PATCH] mm: swap: determine swap device by using page nid

["ying.huang@intel.com" <ying.huang@intel.com>]

On Fri, 2022-04-22 at 14:43 +0800, Aaron Lu wrote:
> On Fri, Apr 22, 2022 at 02:27:45PM +0800, ying.huang@intel.com wrote:
> > On Fri, 2022-04-22 at 14:24 +0800, Aaron Lu wrote:
> > > On Thu, Apr 21, 2022 at 04:34:09PM +0800, ying.huang@intel.com wrote:
> > > > On Thu, 2022-04-21 at 16:17 +0800, Aaron Lu wrote:
> > > > > On Thu, Apr 21, 2022 at 03:49:21PM +0800, ying.huang@intel.com wrote:
> > > 
> > > ... ...
> > > 
> > > > > > For swap-in latency, we can use pmbench, which can output latency
> > > > > > information.
> > > > > > 
> > > > > 
> > > > > OK, I'll give pmbench a run, thanks for the suggestion.
> > > > 
> > > > Better to construct a senario with more swapin than swapout.  For
> > > > example, start a memory eater, then kill it later.
> > > 
> > > What about vm-scalability/case-swapin?
> > > https://git.kernel.org/pub/scm/linux/kernel/git/wfg/vm-scalability.git/tree/case-swapin
> > > 
> > > I think you are pretty familiar with it but still:
> > > 1) it starts $nr_task processes and each mmaps $size/$nr_task area and
> > >    then consumes the memory, after this, it waits for a signal;
> > > 2) start another process to consume $size memory to push the memory in
> > >    step 1) to swap device;
> > > 3) kick processes in step 1) to start accessing their memory, thus
> > >    trigger swapins. The metric of this testcase is the swapin throughput.
> > > 
> > > I plan to restrict the cgroup's limit to $size.
> > > 
> > > Considering there is only one NVMe drive attached to node 0, I will run
> > > the test as described before:
> > > 1) bind processes to run on node 0, allocate on node 1 to test the
> > >    performance when reclaimer's node id is the same as swap device's.
> > > 2) bind processes to run on node 1, allocate on node 0 to test the
> > >    performance when page's node id is the same as swap device's.
> > > 
> > > Ying and Yang,
> > > 
> > > Let me know what you think about the case used and the way the test is
> > > conducted.
> > 
> > The test case looks good to me.  And, do you have a way to measure swap
> > in latency?  Better to compare between enabling and disabling per-node
> 
> By swap in latency, do you mean the time it takes for a fault that is
> served by swap in?
> 
> Since the test is swap in only, I think throughput can tell us the
> average swap in latency?
> 

Yes.  Given the same parallel level, the average swap in latency can be
reflect via throughput.

> > swap device support too to make sure per-node support has performance
> > impact on this system.
> 
> I think we can tell by conducting two more tests:
> 1) bind processes to run on node 0, allocate on node 0;
> 2) bind processes to run on node 1, allocate on node 1.
> If case 1) is faster, we can say per-node support has performance impact
> on this system.

At least we can measure whether cross-node latency matters with this
test.

Best Regards,
Huang, Ying