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

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Message-ID: <20200829145421.GA12470@infradead.org>
Date:   Sat, 29 Aug 2020 15:54:21 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        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 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?