linux-kernel - Re: [PATCH v2 1/3] mm/gup: introduce pin_user

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Message-ID: <2940f38d-be50-cc9d-efac-b472b90c86ad@nvidia.com>
Date:   Sat, 29 Aug 2020 14:57:24 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Ilya Dryomov <idryomov@...il.com>,
        Jens Axboe <axboe@...nel.dk>, <linux-xfs@...r.kernel.org>,
        <linux-fsdevel@...r.kernel.org>, <linux-block@...r.kernel.org>,
        <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] mm/gup: introduce pin_user_page()

On 8/29/20 7:54 AM, Christoph Hellwig wrote:
> On Sat, Aug 29, 2020 at 01:08:51AM -0700, John Hubbard wrote:
>> pin_user_page() is the FOLL_PIN equivalent of get_page().
>>
>> This was always a missing piece of the pin/unpin API calls (early
>> reviewers of pin_user_pages() asked about it, in fact), but until now,
>> it just wasn't needed. Finally though, now that the Direct IO pieces in
>> block/bio are about to be converted to use FOLL_PIN, it turns out that
>> there are some cases in which get_page() and get_user_pages_fast() were
>> both used. Converting those sites requires a drop-in replacement for
>> get_page(), which this patch supplies.
> 
> I find the name really confusing vs pin_user_pages*, as it suggests as
> single version of the same.  It also seems partially wrong, at least
> in the direct I/O case as the only thing pinned here is the zero page.
> 
> So maybe pin_kernel_page is a better name together with an explanation?
> Or just pin_page?
> 

Yes. Both its behavior and use are closer to get_page() than it is to
get_user_pages(). So pin_page() is just right.


thanks,
-- 
John Hubbard
NVIDIA