linux-kernel - Re: [PATCH 05/12] net: mana: Set the DMA device max page size

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Message-ID: <20220517193515.GN63055@ziepe.ca>
Date:   Tue, 17 May 2022 16:35:15 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Long Li <longli@...rosoft.com>
Cc:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Leon Romanovsky <leon@...nel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>
Subject: Re: [PATCH 05/12] net: mana: Set the DMA device max page size

On Tue, May 17, 2022 at 07:32:51PM +0000, Long Li wrote:
> > Subject: Re: [PATCH 05/12] net: mana: Set the DMA device max page size
> > 
> > On Tue, May 17, 2022 at 02:04:29AM -0700, longli@...uxonhyperv.com wrote:
> > > From: Long Li <longli@...rosoft.com>
> > >
> > > The system chooses default 64K page size if the device does not
> > > specify the max page size the device can handle for DMA. This do not
> > > work well when device is registering large chunk of memory in that a
> > > large page size is more efficient.
> > >
> > > Set it to the maximum hardware supported page size.
> > 
> > For RDMA devices this should be set to the largest segment size an ib_sge can
> > take in when posting work. It should not be the page size of MR. 2M is a weird
> > number for that, are you sure it is right?
> 
> Yes, this is the maximum page size used in hardware page tables.

As I said, it should be the size of the sge in the WQE, not the
"hardware page tables"

Jason