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

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Date:   Fri, 22 Apr 2022 14:43:03 +0800
From:   Aaron Lu <aaron.lu@...el.com>
To:     "ying.huang@...el.com" <ying.huang@...el.com>
CC:     Yang Shi <shy828301@...il.com>, Michal Hocko <mhocko@...e.com>,
        "Andrew Morton" <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mm: swap: determine swap device by using page nid

On Fri, Apr 22, 2022 at 02:27:45PM +0800, ying.huang@...el.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@...el.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@...el.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?

> 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.