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

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Date:   Tue, 17 May 2022 19:32:51 +0000
From:   Long Li <longli@...rosoft.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
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

> 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.

Long

> 
> Jason