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Date:   Tue, 27 Oct 2020 10:55:45 +0100
From:   Christoph Hellwig <hch@lst.de>
To:     Jan Kara <jack@suse.cz>
Cc:     John Hubbard <jhubbard@nvidia.com>,
        Jason Gunthorpe <jgg@nvidia.com>, linux-kernel@vger.kernel.org,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Christoph Hellwig <hch@lst.de>,
        Hugh Dickins <hughd@google.com>, Jann Horn <jannh@google.com>,
        Kirill Shutemov <kirill@shutemov.name>,
        Kirill Tkhai <ktkhai@virtuozzo.com>,
        Linux-MM <linux-mm@kvack.org>, Michal Hocko <mhocko@suse.com>,
        Oleg Nesterov <oleg@redhat.com>, Peter Xu <peterx@redhat.com>
Subject: Re: [PATCH 1/2] mm: reorganize internal_get_user_pages_fast()
Message-ID: <20201027095545.GA30382@lst.de>
References: <1-v1-281e425c752f+2df-gup_fork_jgg@nvidia.com> <16c50bb0-431d-5bfb-7b80-a8af0b4da90f@nvidia.com> <20201027093301.GA16090@quack2.suse.cz>
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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.