linux-kernel - Re: [PATCH 1/2] mm: reorganize internal_get_user_pages

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Date:   Tue, 27 Oct 2020 10:55:45 +0100
From:   Christoph Hellwig <hch@....de>
To:     Jan Kara <jack@...e.cz>
Cc:     John Hubbard <jhubbard@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>, linux-kernel@...r.kernel.org,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>,
        Hugh Dickins <hughd@...gle.com>, Jann Horn <jannh@...gle.com>,
        Kirill Shutemov <kirill@...temov.name>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Linux-MM <linux-mm@...ck.org>, Michal Hocko <mhocko@...e.com>,
        Oleg Nesterov <oleg@...hat.com>, Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH 1/2] mm: reorganize internal_get_user_pages_fast()

On Tue, Oct 27, 2020 at 10:33:01AM +0100, Jan Kara wrote:
> Actually there are callers that care about partial success. See e.g.
> iov_iter_get_pages() usage in fs/direct_io.c:dio_refill_pages() or
> bio_iov_iter_get_pages(). These places handle partial success just fine and
> not allowing partial success from GUP could regress things...

But most users do indeed not care.  Maybe an explicit FOLL_PARTIAL to
opt into partial handling could clean up a lot of the mess.  Maybe just
for pin_user_pages for now.