linux-kernel - Re: [PATCH 2/2] mm: set PG_dma_pinned on get_user

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Message-ID: <d4817192-6db0-2f3f-7c67-6078b69686d3@nvidia.com>
Date:   Mon, 18 Jun 2018 10:50:57 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Christoph Hellwig <hch@....de>
CC:     Dan Williams <dan.j.williams@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>, <john.hubbard@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...nel.org>,
        Christopher Lameter <cl@...ux.com>, Jan Kara <jack@...e.cz>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-rdma <linux-rdma@...r.kernel.org>
Subject: Re: [PATCH 2/2] mm: set PG_dma_pinned on get_user_pages*()

On 06/18/2018 01:12 AM, Christoph Hellwig wrote:
> On Sun, Jun 17, 2018 at 01:28:18PM -0700, John Hubbard wrote:
>> Yes. However, my thinking was: get_user_pages() can become a way to indicate that 
>> these pages are going to be treated specially. In particular, the caller
>> does not really want or need to support certain file operations, while the
>> page is flagged this way.
>>
>> If necessary, we could add a new API call.
> 
> That API call is called get_user_pages_longterm.

OK...I had the impression that this was just semi-temporary API for dax, but
given that it's an exported symbol, I guess it really is here to stay.

Anyway, are you thinking that we could set the new page flag here? Or just pointing
out that the other get_user_pages* variants are the wrong place?