From: John Hubbard <jhubbard@nvidia.com>
To: Jerome Glisse <jglisse@redhat.com>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org,
Evgeny Baskakov <ebaskakov@nvidia.com>,
Ralph Campbell <rcampbell@nvidia.com>,
Mark Hairgrove <mhairgrove@nvidia.com>
Subject: Re: [PATCH 15/15] mm/hmm: use device driver encoding for HMM pfn v2
Date: Wed, 21 Mar 2018 16:19:50 -0700 [thread overview]
Message-ID: <98aaf798-12e4-ac52-3913-4fced8a28ce3@nvidia.com> (raw)
In-Reply-To: <20180321155228.GD3214@redhat.com>
On 03/21/2018 08:52 AM, Jerome Glisse wrote:
> On Tue, Mar 20, 2018 at 09:39:27PM -0700, John Hubbard wrote:
>> On 03/19/2018 07:00 PM, jglisse@redhat.com wrote:
>>> From: Jérôme Glisse <jglisse@redhat.com>
>
> [...]
>
<snip>
>>
>> Let's just keep it simple, and go back to the bitmap flags!
>
> This simplify nouveau code and it is the reason why i did that patch.
> I am sure it can simplify NVidia uvm code, i can look into it if you
> want to give pointers. Idea here is that HMM can fill array with some-
> thing that match device driver internal format and avoid the conversion
> step from HMM format to driver format (saving CPU cycles and memory
> doing so). I am open to alternative that give the same end result.
>
> [Just because code is worth 2^32 words :)
>
> Without this patch:
> int nouveau_do_fault(..., ulong addr, unsigned npages, ...)
> {
> uint64_t *hmm_pfns, *nouveau_pfns;
>
> hmm_pfns = kmalloc(sizeof(uint64_t) * npages, GFP_KERNEL);
> nouveau_pfns = kmalloc(sizeof(uint64_t) * npages, GFP_KERNEL);
> hmm_vma_fault(..., hmm_pfns, ...);
>
> for (i = 0; i < npages; ++i) {
> nouveau_pfns[i] = nouveau_pfn_from_hmm_pfn(hmm_pfns[i]);
> }
> ...
> }
>
> With this patch:
> int nouveau_do_fault(..., ulong addr, unsigned npages, ...)
> {
> uint64_t *nouveau_pfns;
>
> nouveau_pfns = kmalloc(sizeof(uint64_t) * npages, GFP_KERNEL);
> hmm_vma_fault(..., nouveau_pfns, ...);
>
> ...
> }
>
> Benefit from this patch is quite obvious to me. Down the road with bit
> more integration between HMM and IOMMU/DMA this can turn into something
> directly ready for hardware consumptions.
>
> Note that you could argue that i can convert nouveau to use HMM format
> but this would not work, first because it requires a lot of changes in
> nouuveau, second because HMM do not have all the flags needed by the
> drivers (nor does HMM need them). HMM being the helper here, i feel it
> is up to HMM to adapt to drivers than the other way around.]
>
OK, if this simplifies Nouveau and potentially other drivers, then I'll
drop my earlier objections! Thanks for explaining what's going on, in detail.
thanks,
--
John Hubbard
NVIDIA
next prev parent reply other threads:[~2018-03-21 23:19 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-20 2:00 [PATCH 00/15] hmm: fixes and documentations v3 jglisse
2018-03-20 2:00 ` [PATCH 01/15] mm/hmm: documentation editorial update to HMM documentation jglisse
2018-03-20 2:00 ` [PATCH 02/15] mm/hmm: fix header file if/else/endif maze v2 jglisse
2018-03-20 2:00 ` [PATCH 03/15] mm/hmm: HMM should have a callback before MM is destroyed v2 jglisse
2018-03-21 4:14 ` John Hubbard
2018-03-21 18:03 ` Jerome Glisse
2018-03-21 22:16 ` John Hubbard
2018-03-21 22:46 ` Jerome Glisse
2018-03-21 23:10 ` John Hubbard
2018-03-21 23:37 ` Jerome Glisse
2018-03-22 0:11 ` John Hubbard
2018-03-22 1:32 ` Jerome Glisse
2018-03-22 1:28 ` [PATCH 03/15] mm/hmm: HMM should have a callback before MM is destroyed v3 jglisse
2018-03-22 6:58 ` John Hubbard
2018-03-20 2:00 ` [PATCH 04/15] mm/hmm: unregister mmu_notifier when last HMM client quit jglisse
2018-03-21 4:24 ` John Hubbard
2018-03-21 18:12 ` Jerome Glisse
2018-03-21 18:16 ` [PATCH 04/15] mm/hmm: unregister mmu_notifier when last HMM client quit v2 jglisse
2018-03-21 23:22 ` John Hubbard
2018-03-21 23:41 ` Jerome Glisse
2018-03-22 22:47 ` John Hubbard
2018-03-22 23:37 ` Jerome Glisse
2018-03-23 0:13 ` John Hubbard
2018-03-23 0:50 ` Jerome Glisse
2018-03-23 0:56 ` John Hubbard
2018-03-22 1:30 ` [PATCH 04/15] mm/hmm: unregister mmu_notifier when last HMM client quit v3 jglisse
2018-03-22 22:36 ` Andrew Morton
2018-03-20 2:00 ` [PATCH 05/15] mm/hmm: hmm_pfns_bad() was accessing wrong struct jglisse
2018-03-20 2:00 ` [PATCH 06/15] mm/hmm: use struct for hmm_vma_fault(), hmm_vma_get_pfns() parameters v2 jglisse
2018-03-20 2:00 ` [PATCH 07/15] mm/hmm: remove HMM_PFN_READ flag and ignore peculiar architecture v2 jglisse
2018-03-20 2:00 ` [PATCH 08/15] mm/hmm: use uint64_t for HMM pfn instead of defining hmm_pfn_t to ulong v2 jglisse
2018-03-20 2:00 ` [PATCH 09/15] mm/hmm: cleanup special vma handling (VM_SPECIAL) jglisse
2018-03-20 2:00 ` [PATCH 10/15] mm/hmm: do not differentiate between empty entry or missing directory v2 jglisse
2018-03-21 5:24 ` John Hubbard
2018-03-21 14:48 ` Jerome Glisse
2018-03-21 23:16 ` John Hubbard
2018-03-20 2:00 ` [PATCH 11/15] mm/hmm: rename HMM_PFN_DEVICE_UNADDRESSABLE to HMM_PFN_DEVICE_PRIVATE jglisse
2018-03-20 2:00 ` [PATCH 12/15] mm/hmm: move hmm_pfns_clear() closer to where it is use jglisse
2018-03-20 2:00 ` [PATCH 13/15] mm/hmm: factor out pte and pmd handling to simplify hmm_vma_walk_pmd() jglisse
2018-03-21 5:07 ` John Hubbard
2018-03-21 15:08 ` Jerome Glisse
2018-03-21 22:36 ` John Hubbard
2018-03-20 2:00 ` [PATCH 14/15] mm/hmm: change hmm_vma_fault() to allow write fault on page basis jglisse
2018-03-20 2:00 ` [PATCH 15/15] mm/hmm: use device driver encoding for HMM pfn v2 jglisse
2018-03-21 4:39 ` John Hubbard
2018-03-21 15:52 ` Jerome Glisse
2018-03-21 23:19 ` John Hubbard [this message]
2018-03-23 0:55 [PATCH 00/15] hmm: fixes and documentations v4 jglisse
2018-03-23 0:55 ` [PATCH 15/15] mm/hmm: use device driver encoding for HMM pfn v2 jglisse
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