linux-kernel - Re: [PATCH v8 10/10] mm: Renumber FOLL_PIN and FOLL

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Message-ID: <863857.1674570312@warthog.procyon.org.uk>
Date:   Tue, 24 Jan 2023 14:25:12 +0000
From:   David Howells <dhowells@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     dhowells@...hat.com, Jason Gunthorpe <jgg@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Matthew Wilcox <willy@...radead.org>,
        Jens Axboe <axboe@...nel.dk>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        linux-fsdevel@...r.kernel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, Christoph Hellwig <hch@....de>,
        linux-mm@...ck.org
Subject: Re: [PATCH v8 10/10] mm: Renumber FOLL_PIN and FOLL_GET down

Christoph Hellwig <hch@...radead.org> wrote:

> > > With the latest series we don't need PAGE_CLEANUP_PUT at all.
> > 
> > We will when it comes to skbuffs.
> 
> I'm a little doubtful of that.

skbuff fragments will be and will have to be a mixture of allocated pages that
need putting and pinned or non-ref'd and non-pinned zerocopy stuff.  I have
posted a patch that works for the limited amount of driverage that I use on my
test machine.

Think network filesystem messages where you have a mixture of protocol bits
generated by the kernel and data provided by direct I/O being sent by zerocopy
(libceph, for example).

David