linux-kernel - Re: [RFC PATCH 0/7] block, fs: convert Direct IO to FOLL

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Date:   Fri, 25 Feb 2022 13:10:53 -0800
From:   John Hubbard <jhubbard@...dia.com>
To:     David Hildenbrand <david@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@...radead.org>,
        Dave Chinner <dchinner@...hat.com>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Theodore Ts'o <tytso@....edu>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Miklos Szeredi <miklos@...redi.hu>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Chaitanya Kulkarni <kch@...dia.com>
Cc:     linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-xfs@...r.kernel.org, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/7] block, fs: convert Direct IO to FOLL_PIN

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