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Date:   Sat, 28 Oct 2023 10:48:00 +0800
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Subject: Re: [PATCH RFC 1/2] RDMA/rxe: don't allow registering !PAGE_SIZE mr
To:     Bart Van Assche <bvanassche@acm.org>,
        Li Zhijian <lizhijian@fujitsu.com>, zyjzyj2000@gmail.com,
        jgg@ziepe.ca, leon@kernel.org, linux-rdma@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org, rpearsonhpe@gmail.com,
        matsuda-daisuke@fujitsu.com
References: <20231027054154.2935054-1-lizhijian@fujitsu.com>
 <53c18b2a-c3b2-4936-b654-12cb5f914622@linux.dev>
 <adad4ee6-ceef-4e45-a13d-048a1377e86f@acm.org>
From:   Zhu Yanjun <yanjun.zhu@linux.dev>
In-Reply-To: <adad4ee6-ceef-4e45-a13d-048a1377e86f@acm.org>
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在 2023/10/28 5:46, Bart Van Assche 写道:
> On 10/27/23 01:17, Zhu Yanjun wrote:
>> When ULP uses folio or compound page, ULP can not work well with RXE 
>> after this commit is applied.
> 
> Isn't it the responsibility of the DMA mapping code to build an sg-list
> for folios? Drivers like ib_srp see an sg-list, whether that comes from

A folio is a way of representing a set of physically contiguous base 
pages. In current implementations of folio, it seems that sg-list is not 
used.

In Folio, some huge pages whose size is not PAGE_SIZE is dma-mapped into 
hardware.

So the page size of folio is not equal to PAGE_SIZE. If this commit is 
applied, it causes potential risks to the future folio.

I have developed some folio work for some NIC and RDMA drivers. In 
Folio, the page size of Folio is possibly not equal to PAGE_SIZE, it is 
multiple PAGE_SIZE. And when folio is dma-mapped to HW, the page size is 
equal to multiple PAGE_SIZE.

In this case, ULP with folio will not work well with current RXE after 
this commit is applied.

Removing page_size in RXE seems a plan for this problem.

Zhu Yanjun


> a folio or from something else.
> 
> Bart.