linux-kernel - Re: [PATCH v2 05/18] mm/gup: introduce pin_user_pages*() and FOLL

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Message-ID: <20191107080706.GB3239@rapoport-lnx>
Date:   Thu, 7 Nov 2019 10:07:07 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     John Hubbard <jhubbard@...dia.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Alex Williamson <alex.williamson@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Chinner <david@...morbit.com>,
        David Airlie <airlied@...ux.ie>,
        "David S . Miller" <davem@...emloft.net>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>,
        Jonathan Corbet <corbet@....net>,
        Jérôme Glisse <jglisse@...hat.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Paul Mackerras <paulus@...ba.org>,
        Shuah Khan <shuah@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>, bpf@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, kvm@...r.kernel.org,
        linux-block@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-media@...r.kernel.org, linux-rdma@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, netdev@...r.kernel.org,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 05/18] mm/gup: introduce pin_user_pages*() and FOLL_PIN

On Tue, Nov 05, 2019 at 11:00:06AM -0800, John Hubbard wrote:
> On 11/5/19 5:10 AM, Mike Rapoport wrote:
> ...
> >> ---
> >>  Documentation/vm/index.rst          |   1 +
> >>  Documentation/vm/pin_user_pages.rst | 212 ++++++++++++++++++++++
> > 
> > I think it belongs to Documentation/core-api.
> 
> Done:
> 
> diff --git a/Documentation/core-api/index.rst b/Documentation/core-api/index.rst
> index ab0eae1c153a..413f7d7c8642 100644
> --- a/Documentation/core-api/index.rst
> +++ b/Documentation/core-api/index.rst
> @@ -31,6 +31,7 @@ Core utilities
>     generic-radix-tree
>     memory-allocation
>     mm-api
> +   pin_user_pages
>     gfp_mask-from-fs-io
>     timekeeping
>     boot-time-mm

Thanks!
 
> ...
> >> diff --git a/Documentation/vm/pin_user_pages.rst b/Documentation/vm/pin_user_pages.rst
> >> new file mode 100644
> >> index 000000000000..3910f49ca98c
> >> --- /dev/null
> >> +++ b/Documentation/vm/pin_user_pages.rst
> >> @@ -0,0 +1,212 @@
> >> +.. SPDX-License-Identifier: GPL-2.0
> >> +
> >> +====================================================
> >> +pin_user_pages() and related calls
> >> +====================================================
> > 
> > I know this is too much to ask, but having pin_user_pages() a part of more
> > general GUP description would be really great :)
> > 
> 
> Yes, definitely. But until I saw the reaction to the pin_user_pages() API
> family, I didn't want to write too much--it could have all been tossed out
> in favor of a whole different API. But now that we've had some initial
> reviews, I'm much more confident in being able to write about the larger 
> API set.
> 
> So yes, I'll put that on my pending list.
> 
> 
> ...
> >> +This document describes the following functions: ::
> >> +
> >> + pin_user_pages
> >> + pin_user_pages_fast
> >> + pin_user_pages_remote
> >> +
> >> + pin_longterm_pages
> >> + pin_longterm_pages_fast
> >> + pin_longterm_pages_remote
> >> +
> >> +Basic description of FOLL_PIN
> >> +=============================
> >> +
> >> +A new flag for get_user_pages ("gup") has been added: FOLL_PIN. FOLL_PIN has
> > 
> > Consider reading this after, say, half a year ;-)
> > 
> 
> OK, OK. I knew when I wrote that that it was not going to stay new forever, but
> somehow failed to write the right thing anyway. :) 
> 
> Here's a revised set of paragraphs:
> 
> Basic description of FOLL_PIN
> =============================
> 
> FOLL_PIN and FOLL_LONGTERM are flags that can be passed to the get_user_pages*()
> ("gup") family of functions. FOLL_PIN has significant interactions and
> interdependencies with FOLL_LONGTERM, so both are covered here.
> 
> Both FOLL_PIN and FOLL_LONGTERM are internal to gup, meaning that neither
> FOLL_PIN nor FOLL_LONGTERM should not appear at the gup call sites. This allows
> the associated wrapper functions  (pin_user_pages() and others) to set the
> correct combination of these flags, and to check for problems as well.

Great, thanks! 
 
> thanks,
> 
> John Hubbard
> NVIDIA

-- 
Sincerely yours,
Mike.