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

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Message-ID: <20220517145949.GH63055@ziepe.ca>
Date:   Tue, 17 May 2022 11:59:49 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     longli@...rosoft.com
Cc:     "K. Y. 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, netdev@...r.kernel.org,
        linux-kernel@...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 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?

Jason