Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Date:   Mon, 11 Jan 2021 12:05:49 -0400
From:   Jason Gunthorpe <jgg@ziepe.ca>
To:     John Hubbard <jhubbard@nvidia.com>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Yu Zhao <yuzhao@google.com>, Andy Lutomirski <luto@kernel.org>,
        Peter Xu <peterx@redhat.com>,
        Pavel Emelyanov <xemul@openvz.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Minchan Kim <minchan@kernel.org>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Hugh Dickins <hughd@google.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Matthew Wilcox <willy@infradead.org>,
        Oleg Nesterov <oleg@redhat.com>, Jann Horn <jannh@google.com>,
        Kees Cook <keescook@chromium.org>,
        Leon Romanovsky <leonro@nvidia.com>, Jan Kara <jack@suse.cz>,
        Kirill Tkhai <ktkhai@virtuozzo.com>,
        Nadav Amit <nadav.amit@gmail.com>, Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH 0/1] mm: restore full accuracy in COW page reuse
Message-ID: <20210111160549.GN504133@ziepe.ca>
References: <20210110004435.26382-1-aarcange@redhat.com>
 <CAHk-=wghqNywtf=sRv_5FmG=+hPGqj=KWakw34tNeoZ1wPuaHg@mail.gmail.com>
 <CAHk-=wj5=1DKbQut1-21EwQbMSghNL3KOSd82rNrBhuG9+eekA@mail.gmail.com>
 <X/prosulFrEoNnoF@redhat.com>
 <CAHk-=wjZTMsv0_GOyQpLRk_5U1r5W8e21f8sV0jykK=z47hjGQ@mail.gmail.com>
 <CAHk-=wgi31FKc9AL6m87+pb2B79V2g_QjdhmtJNW8Pnq2ERQ-Q@mail.gmail.com>
 <45806a5a-65c2-67ce-fc92-dc8c2144d766@nvidia.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <45806a5a-65c2-67ce-fc92-dc8c2144d766@nvidia.com>
Precedence: bulk

On Sun, Jan 10, 2021 at 11:26:57PM -0800, John Hubbard wrote:

> So:
> 
> FOLL_PIN: would use DMA_PIN_COUNTING_BIAS to increment page refcount.
> These are long term pins for dma.
> 
> FOLL_GET: would use GUP_PIN_COUNTING_BIAS to increment page refcount.
> These are not long term pins.

Do we have any places yet that care about the long-term-ness?

The only place long term would matter is if something is waiting for
the page ref count to drop.

Jason