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Message-ID: <9a39e80c-d68f-aad9-b68d-6e578d7b8839@nvidia.com>
Date:   Fri, 25 Feb 2022 13:10:53 -0800
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Subject: Re: [RFC PATCH 0/7] block, fs: convert Direct IO to FOLL_PIN
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To:     David Hildenbrand <david@redhat.com>, Jens Axboe <axboe@kernel.dk>,
        Jan Kara <jack@suse.cz>, Christoph Hellwig <hch@infradead.org>,
        Dave Chinner <dchinner@redhat.com>,
        "Darrick J . Wong" <djwong@kernel.org>,
        Theodore Ts'o <tytso@mit.edu>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Miklos Szeredi <miklos@szeredi.hu>,
        Andrew Morton <akpm@linux-foundation.org>,
        Chaitanya Kulkarni <kch@nvidia.com>
Cc:     linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-xfs@vger.kernel.org, linux-mm@kvack.org,
        LKML <linux-kernel@vger.kernel.org>
References: <20220225085025.3052894-1-jhubbard@nvidia.com>
 <ad29be74-d296-a9fb-41d7-00d2ba15ea5c@redhat.com>
From:   John Hubbard <jhubbard@nvidia.com>
In-Reply-To: <ad29be74-d296-a9fb-41d7-00d2ba15ea5c@redhat.com>
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On 2/25/22 05:12, David Hildenbrand wrote:
> vmsplice is another candidate that uses iov_iter_get_pages() and should

Yes.

> be converted to FOLL_PIN. For that particular user, we have to also pass
> FOLL_LONGTERM -- vmsplice as it stands can block memory hotunplug / CMA
> / ... for all eternity.
> 

Oh, thanks for pointing that out. I was thinking about Direct IO, and
would have overlooked that vmsplice need FOLL_LONGTERM.

I'm still quite vague about which parts of vmsplice are in pipe buffers
(and therefore will *not* get FOLL_PIN pages) and which are in user space
buffers. Just haven't spent enough time with vmsplice yet, hopefully it
will clear up with some study of the code.


thanks,
-- 
John Hubbard
NVIDIA