netdev - Re: [PATCH net-next] net/smc: Allocate pages of SMC-R on ibdev NUMA node

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Date:   Mon, 7 Feb 2022 15:49:26 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Tony Lu <tonylu@...ux.alibaba.com>
Cc:     kgraul@...ux.ibm.com, kuba@...nel.org, davem@...emloft.net,
        netdev@...r.kernel.org, linux-s390@...r.kernel.org,
        RDMA mailing list <linux-rdma@...r.kernel.org>
Subject: Re: [PATCH net-next] net/smc: Allocate pages of SMC-R on ibdev NUMA
 node

On Mon, Feb 07, 2022 at 05:59:58PM +0800, Tony Lu wrote:
> On Mon, Jan 31, 2022 at 09:20:52AM +0200, Leon Romanovsky wrote:
> > On Mon, Jan 31, 2022 at 03:03:00AM +0800, Tony Lu wrote:
> > > Currently, pages are allocated in the process context, for its NUMA node
> > > isn't equal to ibdev's, which is not the best policy for performance.
> > > 
> > > Applications will generally perform best when the processes are
> > > accessing memory on the same NUMA node. When numa_balancing enabled
> > > (which is enabled by most of OS distributions), it moves tasks closer to
> > > the memory of sndbuf or rmb and ibdev, meanwhile, the IRQs of ibdev bind
> > > to the same node usually. This reduces the latency when accessing remote
> > > memory.
> > 
> > It is very subjective per-specific test. I would expect that
> > application will control NUMA memory policies (set_mempolicy(), ...)
> > by itself without kernel setting NUMA node.
> > 
> > Various *_alloc_node() APIs are applicable for in-kernel allocations
> > where user can't control memory policy.
> > 
> > I don't know SMC-R enough, but if I judge from your description, this
> > allocation is controlled by the application.
> 
> The original design of SMC doesn't handle the memory allocation of
> different NUMA node, and the application can't control the NUMA policy
> in SMC.
> 
> It allocates memory according to the NUMA node based on the process
> context, which is determined by the scheduler. If application process
> runs on NUMA node 0, SMC allocates on node 0 and so on, it all depends
> on the scheduler. If RDMA device is attached to node 1, the process runs
> on node 0, it allocates memory on node 0.
> 
> This patch tries to allocate memory on the same NUMA node of RDMA
> device. Applications can't know the current node of RDMA device. The
> scheduler knows the node of memory, and can let applications run on the
> same node of memory and RDMA device.

I don't know, everything explained above is controlled through memory
policy, where application needs to run on same node as ibdev.

Thanks

> 
> Thanks,
> Tony Lu