From: Jason Gunthorpe <jgg@mellanox.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Philip Yang <Philip.Yang@amd.com>,
Ralph Campbell <rcampbell@nvidia.com>,
John Hubbard <jhubbard@nvidia.com>,
Felix.Kuehling@amd.com, dri-devel@lists.freedesktop.org,
linux-mm@kvack.org, Jerome Glisse <jglisse@redhat.com>,
amd-gfx@lists.freedesktop.org
Subject: Re: [PATCH hmm 8/8] mm/hmm: add missing call to hmm_pte_need_fault in HMM_PFN_SPECIAL handling
Date: Tue, 17 Mar 2020 09:53:17 -0300 [thread overview]
Message-ID: <20200317125317.GT13183@mellanox.com> (raw)
In-Reply-To: <20200317123210.GA12058@lst.de>
On Tue, Mar 17, 2020 at 01:32:10PM +0100, Christoph Hellwig wrote:
> On Mon, Mar 16, 2020 at 02:12:01PM +0100, Christoph Hellwig wrote:
> > On Mon, Mar 16, 2020 at 10:04:58AM -0300, Jason Gunthorpe wrote:
> > > > Ok. I had some cleanups like this based of older trees, but if you are
> > > > active in this area I think I'll let you handle it.
> > >
> > > You once said you wanted to loose the weird pfn flags scheme, so
> > > before putting hmm_range_fault in ODP I planned to do that.
> > >
> > > If you have your series someplace send me a URL and I'll look on it
> >
> > I have a local branch I just started hacking on, but it is rather broken
> > based on various discussions we had. But for a basic one I'd suggest
> > something like:
> >
> > - kill HMM_PFN_SPECIAL as it serves no purpose
> > - split the ->pfns array into an input flags (optional) and an output
> > pfn (mandtory) one, using new flags for the input side
> > - replace the output flags/values indirection with a bunch of values
> > encoded in the high bits of a u64, with the rest used for the pfn
>
> Thinking out loud a bit more:
>
> - do we really need HMM_PFN_ERROR, or is just a return value from
> hmm_range_fault enough?
I'm not totally clear on this. The only use for ERROR is to signal to a
non-faulting hmm_range_fault (ie shapshot) that the page should generate a
device fault (ie device SIGSEGV).
We can also handle ERROR by having the device take the fault to CPU,
then fail during a faulting hmm_range_fault and then dropping the
ERROR indication toward the device.
If we already know the page cannot be faulted when we read it it feels
natural to return that too.
I have a patch, that now needs rebasing, which removes the PFN_ERROR
from the faulting cases. So only non-faulting hmm_range_fault users
will see it. faulting users will always see an errno return.
> - because if it is we don't need output flags at all, and the output
> array could be struct pages, which would make for a much easier
> to use API
valid and write is required for the non-faulting case, I don't
think flags can go away.
Being able to do a non-faulting hmm_range_fault is going to be a big
performance win for ODP, this is my interest here.
Jason
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next prev parent reply other threads:[~2020-03-17 14:17 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-11 18:34 [PATCH hmm 0/8] Various error case bug fixes for hmm_range_fault() Jason Gunthorpe
2020-03-11 18:34 ` [PATCH hmm 1/8] mm/hmm: add missing unmaps of the ptep during hmm_vma_handle_pte() Jason Gunthorpe
2020-03-12 1:28 ` Ralph Campbell
2020-03-12 14:24 ` Jason Gunthorpe
2020-03-11 18:35 ` [PATCH hmm 2/8] mm/hmm: don't free the cached pgmap while scanning Jason Gunthorpe
2020-03-12 1:29 ` Ralph Campbell
[not found] ` <20200316090250.GB12439@lst.de>
2020-03-16 18:07 ` Jason Gunthorpe
[not found] ` <20200316181324.GA24533@lst.de>
2020-03-16 19:23 ` Jason Gunthorpe
2020-03-11 18:35 ` [PATCH hmm 3/8] mm/hmm: do not call hmm_vma_walk_hole() while holding a spinlock Jason Gunthorpe
2020-03-12 1:31 ` Ralph Campbell
2020-03-12 8:54 ` Steven Price
2020-03-12 10:28 ` [PATCH] mm/hmm: Simplify hmm_vma_walk_pud slightly Steven Price
2020-03-12 14:27 ` Jason Gunthorpe
2020-03-12 14:40 ` Steven Price
2020-03-12 15:11 ` Jason Gunthorpe
2020-03-12 16:16 ` Steven Price
2020-03-12 16:37 ` Jason Gunthorpe
2020-03-12 17:02 ` Steven Price
2020-03-12 17:17 ` Jason Gunthorpe
2020-03-13 19:55 ` Jason Gunthorpe
2020-03-13 21:04 ` Matthew Wilcox
2020-03-13 22:51 ` Jason Gunthorpe
[not found] ` <20200316090503.GC12439@lst.de>
2020-03-16 12:56 ` [PATCH hmm 3/8] mm/hmm: do not call hmm_vma_walk_hole() while holding a spinlock Jason Gunthorpe
2020-03-11 18:35 ` [PATCH hmm 4/8] mm/hmm: add missing pfns set to hmm_vma_walk_pmd() Jason Gunthorpe
2020-03-12 1:33 ` Ralph Campbell
2020-03-11 18:35 ` [PATCH hmm 5/8] mm/hmm: add missing call to hmm_range_need_fault() before returning EFAULT Jason Gunthorpe
2020-03-12 1:34 ` Ralph Campbell
2020-03-11 18:35 ` [PATCH hmm 6/8] mm/hmm: reorganize how !pte_present is handled in hmm_vma_handle_pte() Jason Gunthorpe
2020-03-12 1:36 ` Ralph Campbell
2020-03-11 18:35 ` [PATCH hmm 7/8] mm/hmm: return -EFAULT when setting HMM_PFN_ERROR on requested valid pages Jason Gunthorpe
2020-03-12 1:36 ` Ralph Campbell
2020-03-12 14:35 ` Jason Gunthorpe
2020-03-11 18:35 ` [PATCH hmm 8/8] mm/hmm: add missing call to hmm_pte_need_fault in HMM_PFN_SPECIAL handling Jason Gunthorpe
2020-03-12 1:38 ` Ralph Campbell
[not found] ` <20200316091347.GH12439@lst.de>
2020-03-16 12:10 ` Jason Gunthorpe
[not found] ` <20200316124953.GC17386@lst.de>
2020-03-16 13:04 ` Jason Gunthorpe
[not found] ` <20200316131201.GA17955@lst.de>
[not found] ` <20200317123210.GA12058@lst.de>
2020-03-17 12:53 ` Jason Gunthorpe [this message]
[not found] ` <20200317130608.GA13030@lst.de>
2020-03-17 13:25 ` Jason Gunthorpe
2020-03-12 19:33 ` [PATCH hmm 9/8] mm/hmm: do not check pmd_protnone twice in hmm_vma_handle_pmd() Jason Gunthorpe
2020-03-12 23:50 ` Ralph Campbell
2020-03-16 18:25 ` [PATCH hmm 0/8] Various error case bug fixes for hmm_range_fault() Jason Gunthorpe
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