Re: [PATCH] mm/gup: Use put_user_page*() instead of put_page*()

From: John Hubbard <jhubbard@nvidia.com>
To: Bharath Vedartham <linux.bhar@gmail.com>
Cc: akpm@linux-foundation.org, ira.weiny@intel.com,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"Dimitri Sivanich" <sivanich@sgi.com>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Alex Williamson" <alex.williamson@redhat.com>,
	"Cornelia Huck" <cohuck@redhat.com>,
	"Jens Axboe" <axboe@kernel.dk>,
	"Alexander Viro" <viro@zeniv.linux.org.uk>,
	"Björn Töpel" <bjorn.topel@intel.com>,
	"Magnus Karlsson" <magnus.karlsson@intel.com>,
	"David S. Miller" <davem@davemloft.net>,
	"Alexei Starovoitov" <ast@kernel.org>,
	"Daniel Borkmann" <daniel@iogearbox.net>,
	"Jakub Kicinski" <jakub.kicinski@netronome.com>,
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	"Alexios Zavras" <alexios.zavras@intel.com>,
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	"Max Filippov" <jcmvbkbc@gmail.com>,
	"Matt Sickler" <Matt.Sickler@daktronics.com>,
	"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
	"Keith Busch" <keith.busch@intel.com>,
	YueHaibing <yuehaibing@huawei.com>,
	linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
	devel@driverdev.osuosl.org, kvm@vger.kernel.org,
	linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org,
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	xdp-newbies@vger.kernel.org, "Jason Gunthorpe" <jgg@ziepe.ca>
Subject: Re: [PATCH] mm/gup: Use put_user_page*() instead of put_page*()
Date: Mon, 15 Jul 2019 11:10:20 -0700	[thread overview]
Message-ID: <1aeb21d9-6dc6-c7d2-58b6-279b1dfc523b@nvidia.com> (raw)
In-Reply-To: <20190715065654.GA3716@bharath12345-Inspiron-5559>

On 7/14/19 11:56 PM, Bharath Vedartham wrote:
> On Sun, Jul 14, 2019 at 04:33:42PM -0700, John Hubbard wrote:
>> On 7/14/19 12:08 PM, Bharath Vedartham wrote:
[...]
>> 1. Pull down https://github.com/johnhubbard/linux/commits/gup_dma_core
>> and find missing conversions: look for any additional missing 
>> get_user_pages/put_page conversions. You've already found a couple missing 
>> ones. I haven't re-run a search in a long time, so there's probably even more.
>> 	a) And find more, after I rebase to 5.3-rc1: people probably are adding
>> 	get_user_pages() calls as we speak. :)
> Shouldn't this be documented then? I don't see any docs for using
> put_user_page*() in v5.2.1 in the memory management API section?

Yes, it needs documentation. My first try (which is still in the above git
repo) was reviewed and found badly wanting, so I'm going to rewrite it. Meanwhile,
I agree that an interim note would be helpful, let me put something together.

[...]
>>     https://github.com/johnhubbard/linux/commits/gup_dma_core
>>
>>     a) gets rebased often, and
>>
>>     b) has a bunch of commits (iov_iter and related) that conflict
>>        with the latest linux.git,
>>
>>     c) has some bugs in the bio area, that I'm fixing, so I don't trust
>>        that's it's safely runnable, for a few more days.
> I assume your repo contains only work related to fixing gup issues and
> not the main repo for gup development? i.e where gup changes are merged?

Correct, this is just a private tree, not a maintainer tree. But I'll try to
keep the gup_dma_core branch something that is usable by others, during the
transition over to put_user_page(), because the page-tracking patches are the
main way to test any put_user_page() conversions.

As Ira said, we're using linux-mm as the real (maintainer) tree.

thanks,
-- 
John Hubbard
NVIDIA