From: John Hubbard <jhubbard@nvidia.com>
To: Jason Gunthorpe <jgg@ziepe.ca>, <linux-mm@kvack.org>,
Ralph Campbell <rcampbell@nvidia.com>
Cc: amd-gfx@lists.freedesktop.org, "Yang,
Philip" <Philip.Yang@amd.com>,
nouveau@lists.freedesktop.org,
"Felix Kuehling" <Felix.Kuehling@amd.com>,
linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
"Christoph Hellwig" <hch@lst.de>,
"Jérôme Glisse" <jglisse@redhat.com>,
"Ben Skeggs" <bskeggs@redhat.com>,
"Alex Deucher" <alexander.deucher@amd.com>,
"Niranjana Vishwanathapura" <niranjana.vishwanathapura@intel.com>,
intel-gfx@lists.freedesktop.org,
"Christian König" <christian.koenig@amd.com>
Subject: Re: [PATCH hmm v2 2/5] mm/hmm: make hmm_range_fault return 0 or -1
Date: Mon, 4 May 2020 17:20:58 -0700 [thread overview]
Message-ID: <9cf9f4f0-58b7-1992-6c6e-eed226ba42c0@nvidia.com> (raw)
In-Reply-To: <2-v2-b4e84f444c7d+24f57-hmm_no_flags_jgg@mellanox.com>
On 2020-05-01 11:20, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg@mellanox.com>
>
> hmm_vma_walk->last is supposed to be updated after every write to the
> pfns, so that it can be returned by hmm_range_fault(). However, this is
> not done consistently. Fortunately nothing checks the return code of
> hmm_range_fault() for anything other than error.
>
> More importantly last must be set before returning -EBUSY as it is used to
> prevent reading an output pfn as an input flags when the loop restarts.
>
> For clarity and simplicity make hmm_range_fault() return 0 or -ERRNO. Only
> set last when returning -EBUSY.
Yes, this is also a nice simplification.
> ...
> @@ -590,10 +580,13 @@ long hmm_range_fault(struct hmm_range *range)
> return -EBUSY;
> ret = walk_page_range(mm, hmm_vma_walk.last, range->end,
> &hmm_walk_ops, &hmm_vma_walk);
> + /*
> + * When -EBUSY is returned the loop restarts with
> + * hmm_vma_walk.last set to an address that has not been stored
> + * in pfns. All entries < last in the pfn array are set to their
> + * output, and all >= are still at their input values.
> + */
I'm glad you added that comment. This is much easier to figure out with
that in place. After poking around this patch and eventually understanding the
.last handling, I wondered if you might like this slightly tweaked wording
instead:
/*
* Each of the hmm_walk_ops routines returns -EBUSY if and only
* hmm_vma_walk.last has been set to an address that has not yet
* been stored in pfns. All entries < last in the pfn array are
* set to their output, and all >= are still at their input
* values.
*/
Either way,
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
thanks,
--
John Hubbard
NVIDIA
> } while (ret == -EBUSY);
> -
> - if (ret)
> - return ret;
> - return (hmm_vma_walk.last - range->start) >> PAGE_SHIFT;
> + return ret;
> }
> EXPORT_SYMBOL(hmm_range_fault);
>
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next prev parent reply other threads:[~2020-05-05 0:21 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-01 18:20 [PATCH hmm v2 0/5] Adjust hmm_range_fault() API Jason Gunthorpe
2020-05-01 18:20 ` [PATCH hmm v2 1/5] mm/hmm: make CONFIG_DEVICE_PRIVATE into a select Jason Gunthorpe
2020-05-02 5:47 ` John Hubbard
2020-05-10 0:16 ` Andrew Morton
2020-05-11 13:49 ` Jason Gunthorpe
2020-05-01 18:20 ` [PATCH hmm v2 2/5] mm/hmm: make hmm_range_fault return 0 or -1 Jason Gunthorpe
2020-05-05 0:20 ` John Hubbard [this message]
2020-05-01 18:20 ` [PATCH hmm v2 3/5] drm/amdgpu: remove dead code after hmm_range_fault() Jason Gunthorpe
2020-05-01 18:20 ` [PATCH hmm v2 4/5] mm/hmm: remove HMM_PFN_SPECIAL Jason Gunthorpe
2020-05-05 0:23 ` John Hubbard
2020-05-01 18:20 ` [PATCH hmm v2 5/5] mm/hmm: remove the customizable pfn format from hmm_range_fault Jason Gunthorpe
2020-05-02 0:53 ` Ralph Campbell
2020-05-06 16:18 ` Jason Gunthorpe
2020-05-05 1:30 ` John Hubbard
2020-05-06 16:21 ` Jason Gunthorpe
2020-05-06 18:45 ` [PATCH hmm v2 0/5] Adjust hmm_range_fault() API Jason Gunthorpe
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