netdev - Re: [PATCH 00/12] block/bio, fs: convert put_page() to put_user

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Date:   Tue, 6 Aug 2019 23:34:48 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Christoph Hellwig <hch@...radead.org>, john.hubbard@...il.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Anna Schumaker <anna.schumaker@...app.com>,
        "David S . Miller" <davem@...emloft.net>,
        Dominique Martinet <asmadeus@...ewreck.org>,
        Eric Van Hensbergen <ericvh@...il.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jason Wang <jasowang@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Latchesar Ionkov <lucho@...kov.net>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Trond Myklebust <trond.myklebust@...merspace.com>,
        Christoph Hellwig <hch@....de>,
        Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
        LKML <linux-kernel@...r.kernel.org>, ceph-devel@...r.kernel.org,
        kvm@...r.kernel.org, linux-block@...r.kernel.org,
        linux-cifs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-rdma@...r.kernel.org,
        netdev@...r.kernel.org, samba-technical@...ts.samba.org,
        v9fs-developer@...ts.sourceforge.net,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH 00/12] block/bio, fs: convert put_page() to
 put_user_page*()

On Mon, Aug 05, 2019 at 03:54:35PM -0700, John Hubbard wrote:
> On 7/23/19 11:17 PM, Christoph Hellwig wrote:
> > On Tue, Jul 23, 2019 at 09:25:06PM -0700, john.hubbard@...il.com wrote:
> >> * Store, in the iov_iter, a "came from gup (get_user_pages)" parameter.
> >>   Then, use the new iov_iter_get_pages_use_gup() to retrieve it when
> >>   it is time to release the pages. That allows choosing between put_page()
> >>   and put_user_page*().
> >>
> >> * Pass in one more piece of information to bio_release_pages: a "from_gup"
> >>   parameter. Similar use as above.
> >>
> >> * Change the block layer, and several file systems, to use
> >>   put_user_page*().
> > 
> > I think we can do this in a simple and better way.  We have 5 ITER_*
> > types.  Of those ITER_DISCARD as the name suggests never uses pages, so
> > we can skip handling it.  ITER_PIPE is rejected іn the direct I/O path,
> > which leaves us with three.
> > 
> 
> Hi Christoph,
> 
> Are you working on anything like this?

I was hoping I could steer you towards it.  But if you don't want to do
it yourself I'll add it to my ever growing todo list.

> Or on the put_user_bvec() idea?

I have a prototype from two month ago:

http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/gup-bvec

but that only survived the most basic testing, so it'll need more work,
which I'm not sure when I'll find time for.