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From: Michal Hocko <mhocko@kernel.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: "Christoph Hellwig" <hch@lst.de>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Jason Gunthorpe" <jgg@mellanox.com>,
	"Ben Skeggs" <bskeggs@redhat.com>,
	"Linux MM" <linux-mm@kvack.org>,
	nouveau@lists.freedesktop.org,
	"Maling list - DRI developers" <dri-devel@lists.freedesktop.org>,
	linux-nvdimm <linux-nvdimm@lists.01.org>,
	linux-pci@vger.kernel.org,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 05/22] mm: export alloc_pages_vma
Date: Tue, 25 Jun 2019 21:00:38 +0200
Message-ID: <20190625190038.GK11400@dhcp22.suse.cz> (raw)
In-Reply-To: <CAPcyv4j1e5dbBHnc+wmtsNUyFbMK_98WxHNwuD_Vxo4dX9Ce=Q@mail.gmail.com>

On Tue 25-06-19 11:03:53, Dan Williams wrote:
> On Tue, Jun 25, 2019 at 8:01 AM Michal Hocko <mhocko@kernel.org> wrote:
> >
> > On Tue 25-06-19 09:23:17, Christoph Hellwig wrote:
> > > On Mon, Jun 24, 2019 at 11:24:48AM -0700, Dan Williams wrote:
> > > > I asked for this simply because it was not exported historically. In
> > > > general I want to establish explicit export-type criteria so the
> > > > community can spend less time debating when to use EXPORT_SYMBOL_GPL
> > > > [1].
> > > >
> > > > The thought in this instance is that it is not historically exported
> > > > to modules and it is safer from a maintenance perspective to start
> > > > with GPL-only for new symbols in case we don't want to maintain that
> > > > interface long-term for out-of-tree modules.
> > > >
> > > > Yes, we always reserve the right to remove / change interfaces
> > > > regardless of the export type, but history has shown that external
> > > > pressure to keep an interface stable (contrary to
> > > > Documentation/process/stable-api-nonsense.rst) tends to be less for
> > > > GPL-only exports.
> > >
> > > Fully agreed.  In the end the decision is with the MM maintainers,
> > > though, although I'd prefer to keep it as in this series.
> >
> > I am sorry but I am not really convinced by the above reasoning wrt. to
> > the allocator API and it has been a subject of many changes over time. I
> > do not remember a single case where we would be bending the allocator
> > API because of external modules and I am pretty sure we will push back
> > heavily if that was the case in the future.
> 
> This seems to say that you have no direct experience of dealing with
> changing symbols that that a prominent out-of-tree module needs? GPU
> drivers and the core-mm are on a path to increase their cooperation on
> memory management mechanisms over time, and symbol export changes for
> out-of-tree GPU drivers have been a significant source of friction in
> the past.

I have an experience e.g. to rework semantic of some gfp flags and that is
something that users usualy get wrong and never heard that an out of
tree code would insist on an old semantic and pushing us to the corner.

> > So in this particular case I would go with consistency and export the
> > same way we do with other functions. Also we do not want people to
> > reinvent this API and screw that like we have seen in other cases when
> > external modules try reimplement core functionality themselves.
> 
> Consistency is a weak argument when the cost to the upstream community
> is negligible. If the same functionality was available via another /
> already exported interface *that* would be an argument to maintain the
> existing export policy. "Consistency" in and of itself is not a
> precedent we can use more widely in default export-type decisions.
> 
> Effectively I'm arguing EXPORT_SYMBOL_GPL by default with a later
> decision to drop the _GPL. Similar to how we are careful to mark sysfs
> interfaces in Documentation/ABI/ that we are not fully committed to
> maintaining over time, or are otherwise so new that there is not yet a
> good read on whether they can be made permanent.

Documentation/process/stable-api-nonsense.rst
Really. If you want to play with GPL vs. EXPORT_SYMBOL else this is up
to you but I do not see any technical argument to make this particular
interface to the page allocator any different from all others that are
exported to modules.
-- 
Michal Hocko
SUSE Labs

  reply index

Thread overview: 103+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-13  9:43 dev_pagemap related cleanups Christoph Hellwig
2019-06-13  9:43 ` [PATCH 01/22] mm: remove the unused ARCH_HAS_HMM_DEVICE Kconfig option Christoph Hellwig
2019-06-13 18:30   ` Jason Gunthorpe
2019-06-13  9:43 ` [PATCH 02/22] mm: remove the struct hmm_device infrastructure Christoph Hellwig
2019-06-13 18:46   ` Jason Gunthorpe
2019-06-13 23:06   ` [Nouveau] " John Hubbard
2019-06-13  9:43 ` [PATCH 03/22] mm: remove hmm_devmem_add_resource Christoph Hellwig
2019-06-13 18:52   ` Jason Gunthorpe
2019-06-14  6:19     ` Christoph Hellwig
2019-06-14  0:54   ` [Nouveau] " John Hubbard
2019-06-20 19:32   ` Michal Hocko
2019-06-13  9:43 ` [PATCH 04/22] mm: don't clear ->mapping in hmm_devmem_free Christoph Hellwig
2019-06-13 19:05   ` Jason Gunthorpe
2019-06-14  6:21     ` Christoph Hellwig
2019-06-14  1:46   ` John Hubbard
2019-06-20 19:36   ` Michal Hocko
2019-06-13  9:43 ` [PATCH 05/22] mm: export alloc_pages_vma Christoph Hellwig
2019-06-14  1:47   ` John Hubbard
2019-06-14  6:23     ` Christoph Hellwig
2019-06-20 19:17   ` Michal Hocko
2019-06-24 18:24     ` Dan Williams
2019-06-25  7:23       ` Christoph Hellwig
2019-06-25 15:00         ` Michal Hocko
2019-06-25 18:03           ` Dan Williams
2019-06-25 19:00             ` Michal Hocko [this message]
2019-06-25 19:52               ` Dan Williams
2019-06-26  5:46                 ` Michal Hocko
2019-06-26 16:14                   ` Dan Williams
2019-06-27  6:41                     ` Michal Hocko
2019-06-13  9:43 ` [PATCH 06/22] mm: factor out a devm_request_free_mem_region helper Christoph Hellwig
2019-06-13 19:16   ` Jason Gunthorpe
2019-06-14  6:24     ` Christoph Hellwig
2019-06-15  2:21   ` John Hubbard
2019-06-15 14:30     ` Christoph Hellwig
2019-06-13  9:43 ` [PATCH 07/22] memremap: move dev_pagemap callbacks into a separate structure Christoph Hellwig
2019-06-13 19:18   ` Jason Gunthorpe
2019-06-13 20:14   ` Logan Gunthorpe
2019-06-13  9:43 ` [PATCH 08/22] memremap: pass a struct dev_pagemap to ->kill Christoph Hellwig
2019-06-13 19:26   ` Jason Gunthorpe
2019-06-13 20:12   ` Logan Gunthorpe
2019-06-13 20:15     ` Dan Williams
2019-06-13  9:43 ` [PATCH 09/22] memremap: lift the devmap_enable manipulation into devm_memremap_pages Christoph Hellwig
2019-06-13 19:34   ` Jason Gunthorpe
2019-06-13 20:13     ` Dan Williams
2019-06-14  6:28     ` Christoph Hellwig
2019-06-13  9:43 ` [PATCH 10/22] memremap: add a migrate callback to struct dev_pagemap_ops Christoph Hellwig
2019-06-13 23:42   ` Ralph Campbell
2019-06-14  6:33     ` Christoph Hellwig
2019-06-13  9:43 ` [PATCH 11/22] memremap: remove the data field in struct dev_pagemap Christoph Hellwig
2019-06-13 19:37   ` Jason Gunthorpe
2019-06-13  9:43 ` [PATCH 12/22] memremap: provide an optional internal refcount " Christoph Hellwig
2019-06-13  9:43 ` [PATCH 13/22] device-dax: use the dev_pagemap internal refcount Christoph Hellwig
2019-06-14  0:22   ` Ira Weiny
2019-06-14  6:35     ` Christoph Hellwig
2019-06-13  9:43 ` [PATCH 14/22] nouveau: use alloc_page_vma directly Christoph Hellwig
2019-06-13 19:39   ` Jason Gunthorpe
2019-06-13  9:43 ` [PATCH 15/22] nouveau: use devm_memremap_pages directly Christoph Hellwig
2019-06-13  9:43 ` [PATCH 16/22] mm: remove hmm_vma_alloc_locked_page Christoph Hellwig
2019-06-13  9:43 ` [PATCH 17/22] mm: remove hmm_devmem_add Christoph Hellwig
2019-06-13 19:42   ` Jason Gunthorpe
2019-06-14  6:39     ` Christoph Hellwig
2019-06-13  9:43 ` [PATCH 18/22] mm: mark DEVICE_PUBLIC as broken Christoph Hellwig
2019-06-13 19:44   ` Jason Gunthorpe
2019-06-13 19:53     ` Ralph Campbell
2019-06-13 19:58       ` Jason Gunthorpe
2019-06-14  0:43         ` Ira Weiny
2019-06-14  1:23           ` John Hubbard
2019-06-19 19:27             ` Jason Gunthorpe
2019-06-19 19:46               ` Dan Williams
2019-06-26  3:15               ` John Hubbard
2019-06-26  5:45                 ` Michal Hocko
2019-06-26  6:07                   ` John Hubbard
2019-06-14  6:43           ` Christoph Hellwig
2019-06-20 19:26   ` Michal Hocko
2019-06-25  7:29     ` Christoph Hellwig
2019-06-25 11:44       ` Jason Gunthorpe
2019-06-25 11:59         ` Christoph Hellwig
2019-06-13  9:43 ` [PATCH 19/22] mm: simplify ZONE_DEVICE page private data Christoph Hellwig
2019-06-13  9:43 ` [PATCH 20/22] mm: sort out the DEVICE_PRIVATE Kconfig mess Christoph Hellwig
2019-06-13 19:55   ` Jason Gunthorpe
2019-06-13  9:43 ` [PATCH 21/22] mm: remove the HMM config option Christoph Hellwig
2019-06-13 20:01   ` Jason Gunthorpe
2019-06-14  6:47     ` Christoph Hellwig
2019-06-13  9:43 ` [PATCH 22/22] mm: don't select MIGRATE_VMA_HELPER from HMM_MIRROR Christoph Hellwig
2019-06-13 20:04   ` Jason Gunthorpe
2019-06-14  1:53   ` [Nouveau] " John Hubbard
2019-06-14  6:48     ` Christoph Hellwig
2019-06-13 14:16 ` dev_pagemap related cleanups Jason Gunthorpe
2019-06-14  6:12   ` Christoph Hellwig
2019-06-13 18:27 ` Dan Williams
2019-06-13 20:17   ` Logan Gunthorpe
2019-06-13 20:21     ` Dan Williams
2019-06-13 20:24       ` Logan Gunthorpe
2019-06-13 20:48         ` Andrew Morton
2019-06-13 20:40   ` Jason Gunthorpe
2019-06-13 21:21     ` Christoph Hellwig
2019-06-13 23:10       ` Jason Gunthorpe
2019-06-14  6:14         ` Christoph Hellwig
2019-06-14  0:31     ` Ira Weiny
2019-06-14  6:13   ` Christoph Hellwig
2019-06-15  1:14     ` Dan Williams
2019-06-15  8:33       ` Christoph Hellwig
2019-06-15 18:09         ` Dan Williams

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