From: Jerome Glisse <jglisse@redhat.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: "Andrew Morton" <akpm@linux-foundation.org>,
"Linux MM" <linux-mm@kvack.org>,
"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Felix Kuehling" <Felix.Kuehling@amd.com>,
"Christian König" <christian.koenig@amd.com>,
"Ralph Campbell" <rcampbell@nvidia.com>,
"John Hubbard" <jhubbard@nvidia.com>,
"Jason Gunthorpe" <jgg@mellanox.com>
Subject: Re: [PATCH 00/10] HMM updates for 5.1
Date: Mon, 18 Mar 2019 15:28:58 -0400 [thread overview]
Message-ID: <20190318192858.GC6786@redhat.com> (raw)
In-Reply-To: <CAPcyv4gLyKkboZ-ucHubiHgdpF4i9w+XKhPujjJ=dwU9Vox=Bg@mail.gmail.com>
On Mon, Mar 18, 2019 at 12:18:38PM -0700, Dan Williams wrote:
> On Mon, Mar 18, 2019 at 11:55 AM Jerome Glisse <jglisse@redhat.com> wrote:
> >
> > On Mon, Mar 18, 2019 at 11:30:15AM -0700, Dan Williams wrote:
> > > On Mon, Mar 18, 2019 at 10:04 AM Jerome Glisse <jglisse@redhat.com> wrote:
> > > >
> > > > On Wed, Mar 13, 2019 at 09:10:04AM -0700, Andrew Morton wrote:
> > > > > On Tue, 12 Mar 2019 21:27:06 -0400 Jerome Glisse <jglisse@redhat.com> wrote:
> > > > >
> > > > > > Andrew you will not be pushing this patchset in 5.1 ?
> > > > >
> > > > > I'd like to. It sounds like we're converging on a plan.
> > > > >
> > > > > It would be good to hear more from the driver developers who will be
> > > > > consuming these new features - links to patchsets, review feedback,
> > > > > etc. Which individuals should we be asking? Felix, Christian and
> > > > > Jason, perhaps?
> > > > >
> > > >
> > > > So i am guessing you will not send this to Linus ? Should i repost ?
> > > > This patchset has 2 sides, first side is just reworking the HMM API
> > > > to make something better in respect to process lifetime. AMD folks
> > > > did find that helpful [1]. This rework is also necessary to ease up
> > > > the convertion of ODP to HMM [2] and Jason already said that he is
> > > > interested in seing that happening [3]. By missing 5.1 it means now
> > > > that i can not push ODP to HMM in 5.2 and it will be postpone to 5.3
> > > > which is also postoning other work ...
> > > >
> > > > The second side is it adds 2 new helper dma map and dma unmap both
> > > > are gonna be use by ODP and latter by nouveau (after some other
> > > > nouveau changes are done). This new functions just do dma_map ie:
> > > > hmm_dma_map() {
> > > > existing_hmm_api()
> > > > for_each_page() {
> > > > dma_map_page()
> > > > }
> > > > }
> > > >
> > > > Do you want to see anymore justification than that ?
> > >
> > > Yes, why does hmm needs its own dma mapping apis? It seems to
> > > perpetuate the perception that hmm is something bolted onto the side
> > > of the core-mm rather than a native capability.
> >
> > Seriously ?
>
> Yes.
>
> > Kernel is fill with example where common code pattern that are not
> > device specific are turn into helpers and here this is exactly what
> > it is. A common pattern that all device driver will do which is turn
> > into a common helper.
>
> Yes, but we also try not to introduce thin wrappers around existing
> apis. If the current dma api does not understand some hmm constraint
> I'm questioning why not teach the dma api that constraint and make it
> a native capability rather than asking the driver developer to
> understand the rules about when to use dma_map_page() vs
> hmm_dma_map().
There is nothing special here, existing_hmm_api() return an array of
page and the new helper just call dma_map_page for each entry in that
array. If it fails it undo everything so that error handling is share.
So i am not playing trick with DMA API i am just providing an helper
for a common pattern. Maybe the name confuse you but the pseudo should
be selft explanatory:
Before
mydriver_mirror_range() {
err = existing_hmm_mirror_api(pages)
if (err) {...}
for_each_page(pages) {
pas[i]= dma_map_page()
if (dma_error(pas[i])) { ... }
}
// use pas[]
}
After
mydriver_mirror_range() {
err = hmm_range_dma_map(pas)
if (err) { ... }
// use pas[]
}
So there is no rule of using one or the other. In the end it is the
same code. But instead of duplicating it in multiple drivers it is
share.
>
> For example I don't think we want to end up with more headers like
> include/linux/pci-dma-compat.h.
>
> > Moreover this allow to share the same error code handling accross
> > driver when mapping one page fails. So this avoid the needs to
> > duplicate same boiler plate code accross different drivers.
> >
> > Is code factorization not a good thing ? Should i duplicate every-
> > thing in every single driver ?
>
> I did not ask for duplication, I asked why is it not more deeply integrated.
Because it is a common code pattern for HMM user not for DMA user.
> > If that's not enough, this will also allow to handle peer to peer
> > and i posted patches for that [1] and again this is to avoid
> > duplicating common code accross different drivers.
>
> I went looking for the hmm_dma_map() patches on the list but could not
> find them, so I was reacting to the "This new functions just do
> dma_map", and wondered if that was the full extent of the
> justification.
They are here [1] patch 7 in this patch serie
Cheers,
Jérôme
[1] https://lkml.org/lkml/2019/1/29/1016
next prev parent reply other threads:[~2019-03-18 19:29 UTC|newest]
Thread overview: 98+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-29 16:54 [PATCH 00/10] HMM updates for 5.1 jglisse
2019-01-29 16:54 ` [PATCH 01/10] mm/hmm: use reference counting for HMM struct jglisse
2019-02-20 23:47 ` John Hubbard
2019-02-20 23:59 ` Jerome Glisse
2019-02-21 0:06 ` John Hubbard
2019-02-21 0:15 ` Jerome Glisse
2019-02-21 0:32 ` John Hubbard
2019-02-21 0:37 ` Jerome Glisse
2019-02-21 0:42 ` John Hubbard
2019-01-29 16:54 ` [PATCH 02/10] mm/hmm: do not erase snapshot when a range is invalidated jglisse
2019-02-20 23:58 ` John Hubbard
2019-01-29 16:54 ` [PATCH 03/10] mm/hmm: improve and rename hmm_vma_get_pfns() to hmm_range_snapshot() jglisse
2019-02-21 0:25 ` John Hubbard
2019-02-21 0:28 ` Jerome Glisse
2019-01-29 16:54 ` [PATCH 04/10] mm/hmm: improve and rename hmm_vma_fault() to hmm_range_fault() jglisse
2019-01-29 16:54 ` [PATCH 05/10] mm/hmm: improve driver API to work and wait over a range jglisse
2019-01-29 16:54 ` [PATCH 06/10] mm/hmm: add default fault flags to avoid the need to pre-fill pfns arrays jglisse
2019-01-29 16:54 ` [PATCH 07/10] mm/hmm: add an helper function that fault pages and map them to a device jglisse
2019-03-18 20:21 ` Dan Williams
2019-03-18 20:41 ` Jerome Glisse
2019-03-18 21:30 ` Dan Williams
2019-03-18 22:15 ` Jerome Glisse
2019-03-19 3:29 ` Dan Williams
2019-03-19 13:30 ` Jerome Glisse
2019-03-19 8:44 ` Ira Weiny
2019-03-19 17:10 ` Jerome Glisse
2019-03-19 14:10 ` Ira Weiny
2019-01-29 16:54 ` [PATCH 08/10] mm/hmm: support hugetlbfs (snap shoting, faulting and DMA mapping) jglisse
2019-01-29 16:54 ` [PATCH 09/10] mm/hmm: allow to mirror vma of a file on a DAX backed filesystem jglisse
2019-01-29 18:41 ` Dan Williams
2019-01-29 19:31 ` Jerome Glisse
2019-01-29 20:51 ` Dan Williams
2019-01-29 21:21 ` Jerome Glisse
2019-01-30 2:32 ` Dan Williams
2019-01-30 3:03 ` Jerome Glisse
2019-01-30 17:25 ` Dan Williams
2019-01-30 18:36 ` Jerome Glisse
2019-01-31 3:28 ` Dan Williams
2019-01-31 4:16 ` Jerome Glisse
2019-01-31 5:44 ` Dan Williams
2019-03-05 22:16 ` Andrew Morton
2019-03-06 4:20 ` Dan Williams
2019-03-06 15:51 ` Jerome Glisse
2019-03-06 15:57 ` Dan Williams
2019-03-06 16:03 ` Jerome Glisse
2019-03-06 16:06 ` Dan Williams
2019-03-07 17:46 ` Andrew Morton
2019-03-07 18:56 ` Jerome Glisse
2019-03-12 3:13 ` Dan Williams
2019-03-12 15:25 ` Jerome Glisse
2019-03-12 16:06 ` Dan Williams
2019-03-12 19:06 ` Jerome Glisse
2019-03-12 19:30 ` Dan Williams
2019-03-12 20:34 ` Dave Chinner
2019-03-13 1:06 ` Dan Williams
2019-03-12 21:52 ` Andrew Morton
2019-03-13 0:10 ` Jerome Glisse
2019-03-13 0:46 ` Dan Williams
2019-03-13 1:00 ` Jerome Glisse
2019-03-13 16:06 ` Andrew Morton
2019-03-13 18:39 ` Jerome Glisse
2019-03-06 15:49 ` Jerome Glisse
2019-03-06 22:18 ` Andrew Morton
2019-03-07 0:36 ` Jerome Glisse
2019-01-29 16:54 ` [PATCH 10/10] mm/hmm: add helpers for driver to safely take the mmap_sem jglisse
2019-02-20 21:59 ` John Hubbard
2019-02-20 22:19 ` Jerome Glisse
2019-02-20 22:40 ` John Hubbard
2019-02-20 23:09 ` Jerome Glisse
2019-02-20 23:17 ` [PATCH 00/10] HMM updates for 5.1 John Hubbard
2019-02-20 23:36 ` Jerome Glisse
2019-02-22 23:31 ` Ralph Campbell
2019-03-13 1:27 ` Jerome Glisse
2019-03-13 16:10 ` Andrew Morton
2019-03-13 18:01 ` Jason Gunthorpe
2019-03-13 18:33 ` Jerome Glisse
2019-03-18 17:00 ` Kuehling, Felix
2019-03-18 17:04 ` Jerome Glisse
2019-03-18 18:30 ` Dan Williams
2019-03-18 18:54 ` Jerome Glisse
2019-03-18 19:18 ` Dan Williams
2019-03-18 19:28 ` Jerome Glisse [this message]
2019-03-18 19:36 ` Dan Williams
2019-03-19 16:40 ` Andrew Morton
2019-03-19 16:58 ` Jerome Glisse
2019-03-19 17:12 ` Andrew Morton
2019-03-19 17:18 ` Jerome Glisse
2019-03-19 17:33 ` Dan Williams
2019-03-19 17:45 ` Jerome Glisse
2019-03-19 18:42 ` Dan Williams
2019-03-19 19:05 ` Jerome Glisse
2019-03-19 19:13 ` Dan Williams
2019-03-19 14:18 ` Ira Weiny
2019-03-19 22:24 ` Jerome Glisse
2019-03-19 19:18 ` Jerome Glisse
2019-03-19 20:25 ` Jerome Glisse
2019-03-19 21:51 ` Stephen Rothwell
2019-03-19 18:51 ` Deucher, Alexander
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