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Date:   Tue, 1 Feb 2022 08:31:34 -0400
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     John Hubbard <jhubbard@nvidia.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Peter Xu <peterx@redhat.com>,
        David Hildenbrand <david@redhat.com>, Jan Kara <jack@suse.cz>,
        Claudio Imbrenda <imbrenda@linux.ibm.com>,
        "Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
        Alex Williamson <alex.williamson@redhat.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        LKML <linux-kernel@vger.kernel.org>, linux-mm@kvack.org
Subject: Re: [PATCH v2 4/4] mm/gup: remove get_user_pages_locked()
Message-ID: <20220201123134.GZ8034@ziepe.ca>
References: <20220201101108.306062-1-jhubbard@nvidia.com>
 <20220201101108.306062-5-jhubbard@nvidia.com>
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On Tue, Feb 01, 2022 at 02:11:08AM -0800, John Hubbard wrote:
> There is only one caller of get_user_pages_locked(). The purpose of
> get_user_pages_locked() is to allow for unlocking the mmap_lock when
> reading a page from the disk during a page fault (hidden behind
> VM_FAULT_RETRY). The idea is to reduce contention on the heavily-used
> mmap_lock. (Thanks to Jan Kara for clearly pointing that out, and in
> fact I've used some of his wording here.)
> 
> However, it is unlikely for lookup_node() to take a page fault. With
> that in mind, change over to calling get_user_pages_fast(). This
> simplifies the code, runs a little faster in the expected case, and
> allows removing get_user_pages_locked() entirely.
> 
> Cc: Jan Kara <jack@suse.cz>
> Suggested-by: Jason Gunthorpe <jgg@ziepe.ca>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  include/linux/mm.h |  2 --
>  mm/gup.c           | 59 ----------------------------------------------
>  mm/mempolicy.c     | 21 +++++++----------
>  3 files changed, 9 insertions(+), 73 deletions(-)

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason