linux-kernel - Re: [PATCH] staging: gasket: Convert get_user_pages*() --> pin_user

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Message-ID: <52f75ec4-a2a0-f979-a3b9-ef016b88907c@nvidia.com>
Date:   Fri, 29 May 2020 00:38:20 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Souptick Joarder <jrdr.linux@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>
CC:     Rob Springer <rspringer@...gle.com>,
        Todd Poynor <toddpoynor@...gle.com>, <benchan@...omium.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "open list:ANDROID DRIVERS" <devel@...verdev.osuosl.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] staging: gasket: Convert get_user_pages*() -->
 pin_user_pages*()

On 2020-05-28 23:27, Souptick Joarder wrote:
> On Fri, May 29, 2020 at 11:46 AM Souptick Joarder <jrdr.linux@...il.com> wrote:
>>
>> On Thu, May 28, 2020 at 4:34 PM Dan Carpenter <dan.carpenter@...cle.com> wrote:
>>>
>>> On Thu, May 28, 2020 at 02:32:42AM +0530, Souptick Joarder wrote:
>>>> This code was using get_user_pages_fast(), in a "Case 2" scenario
>>>> (DMA/RDMA), using the categorization from [1]. That means that it's
>>>> time to convert the get_user_pages_fast() + put_page() calls to
>>>> pin_user_pages_fast() + unpin_user_page() calls.
>>>
>>> You are saying that the page is used for DIO and not DMA, but it sure
>>> looks to me like it is used for DMA.
>>
>> No, I was referring to "Case 2" scenario in change log which means  it is
>> used for DMA, not DIO.

Hi,

Dan, I also uncertain as to how you read this as referring to DIO. Case 2 is
DMA or RDMA, and in fact the proposed commit log says both of those things:
Case 2 and DMA/RDMA. I don't see "DIO" anywhere here...


>>
>>>
>>>     503                          /* Map the page into DMA space. */
>>>     504                          ptes[i].dma_addr =
>>>     505                                  dma_map_page(pg_tbl->device, page, 0, PAGE_SIZE,
>>>     506                                               DMA_BIDIRECTIONAL);
>>>
>>> To be honest, that starting paragraph was confusing.  At first I thought
>>> you were saying gasket was an RDMA driver. :P  I shouldn't have to read
>>> a different document to understand the commit message.  It should be
>>> summarized enough and the other documentation is supplemental.
>>>
>>> "In 2019 we introduced pin_user_pages() and now we are converting
>>> get_user_pages() to the new API as appropriate".
>>
>> As all other similar conversion have similar change logs, so I was trying
>> to maintain the same. John might have a different opinion on this.
> 
> For example, I was referring to few recent similar commits for change logs.
> 
> http://lkml.kernel.org/r/20200519002124.2025955-5-jhubbard@nvidia.com
> https://lore.kernel.org/r/20200518015237.1568940-1-jhubbard@nvidia.com
> 
> 
>>
>> John, Any further opinion ??


Well, I've gotten away with the current wording for quite a few patches so
far, but that sure doesn't mean it's perfect! :)

Maybe adding the words that Dan suggests, above, will suffice? Here:

 >>> "In 2019 we introduced pin_user_pages() and now we are converting
 >>> get_user_pages() to the new API as appropriate".


thanks,
-- 
John Hubbard
NVIDIA