From: Alistair Popple <apopple@nvidia.com>
To: Peter Xu <peterx@redhat.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>, <linux-mm@kvack.org>,
<nouveau@lists.freedesktop.org>, <bskeggs@redhat.com>,
<akpm@linux-foundation.org>, <linux-doc@vger.kernel.org>,
<linux-kernel@vger.kernel.org>, <dri-devel@lists.freedesktop.org>,
<jhubbard@nvidia.com>, <rcampbell@nvidia.com>,
<jglisse@redhat.com>, <hch@infradead.org>, <daniel@ffwll.ch>,
<willy@infradead.org>, <bsingharora@gmail.com>,
Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH v8 5/8] mm: Device exclusive memory access
Date: Wed, 19 May 2021 23:11:55 +1000 [thread overview]
Message-ID: <2569629.VzlulnA7BY@nvdebian> (raw)
In-Reply-To: <YKUBbVuvm5FUJRMl@t490s>
On Wednesday, 19 May 2021 10:15:41 PM AEST Peter Xu wrote:
> External email: Use caution opening links or attachments
>
> On Wed, May 19, 2021 at 09:04:53PM +1000, Alistair Popple wrote:
> > Failing fork() because we couldn't take a lock doesn't seem like the right
> > approach though, especially as there is already existing code that
> > retries. I get this adds complexity though, so would be happy to take a
> > look at cleaning copy_pte_range() up in future.
>
> Yes, I proposed that as this one won't affect any existing applications
> (unlike the existing ones) but only new userspace driver apps that will use
> this new atomic feature.
>
> IMHO it'll be a pity to add extra complexity and maintainance burden into
> fork() if only for keeping the "logical correctness of fork()" however the
> code never triggers. If we start with trylock we'll know whether people
> will use it, since people will complain with a reason when needed; however
> I still doubt whether a sane userspace device driver should fork() within
> busy interaction with the device underneath..
I will refrain from commenting on the sanity or otherwise of doing that :-)
Agree such a scenario seems unlikely in practice (and possibly unreasonable).
Keeping the "logical correctness of fork()" still seems worthwhile to me, but
if the added complexity/maintenance burden for an admittedly fairly specific
feature is going to stop progress here I am happy to take the fail fork
approach. I could then possibly fix it up as a future clean up to
copy_pte_range(). Perhaps others have thoughts?
> In all cases, please still consider to keep them in copy_nonpresent_pte()
> (and if to rework, separating patches would be great).
>
> Thanks,
>
> --
> Peter Xu
next prev parent reply other threads:[~2021-05-19 13:12 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-07 8:42 [PATCH v8 0/8] Add support for SVM atomics in Nouveau Alistair Popple
2021-04-07 8:42 ` [PATCH v8 1/8] mm: Remove special swap entry functions Alistair Popple
2021-05-18 2:17 ` Peter Xu
2021-05-18 11:58 ` Alistair Popple
2021-05-18 14:17 ` Peter Xu
2021-04-07 8:42 ` [PATCH v8 2/8] mm/swapops: Rework swap entry manipulation code Alistair Popple
2021-04-07 8:42 ` [PATCH v8 3/8] mm/rmap: Split try_to_munlock from try_to_unmap Alistair Popple
2021-05-18 20:04 ` Liam Howlett
2021-05-19 12:38 ` Alistair Popple
2021-05-20 20:24 ` Liam Howlett
2021-05-21 2:23 ` Alistair Popple
2021-04-07 8:42 ` [PATCH v8 4/8] mm/rmap: Split migration into its own function Alistair Popple
2021-04-07 8:42 ` [PATCH v8 5/8] mm: Device exclusive memory access Alistair Popple
2021-05-18 2:08 ` Peter Xu
2021-05-18 13:19 ` Alistair Popple
2021-05-18 17:27 ` Peter Xu
2021-05-18 17:33 ` Jason Gunthorpe
2021-05-18 18:01 ` Peter Xu
2021-05-18 19:45 ` Jason Gunthorpe
2021-05-18 20:29 ` Peter Xu
2021-05-18 23:03 ` Jason Gunthorpe
2021-05-18 23:45 ` Peter Xu
2021-05-19 11:04 ` Alistair Popple
2021-05-19 12:15 ` Peter Xu
2021-05-19 13:11 ` Alistair Popple [this message]
2021-05-19 14:04 ` Peter Xu
2021-05-19 13:28 ` Jason Gunthorpe
2021-05-19 14:09 ` Peter Xu
2021-05-19 18:11 ` Jason Gunthorpe
2021-05-19 11:35 ` Alistair Popple
2021-05-19 12:21 ` Peter Xu
2021-05-19 12:46 ` Alistair Popple
2021-05-21 6:53 ` Alistair Popple
2021-05-18 21:16 ` Peter Xu
2021-05-19 10:49 ` Alistair Popple
2021-05-19 12:24 ` Peter Xu
2021-05-19 12:46 ` Alistair Popple
2021-04-07 8:42 ` [PATCH v8 6/8] mm: Selftests for exclusive device memory Alistair Popple
2021-04-07 8:42 ` [PATCH v8 7/8] nouveau/svm: Refactor nouveau_range_fault Alistair Popple
2021-04-07 8:42 ` [PATCH v8 8/8] nouveau/svm: Implement atomic SVM access Alistair Popple
2021-05-21 4:04 ` Ben Skeggs
2021-05-06 7:43 ` [PATCH v8 0/8] Add support for SVM atomics in Nouveau Alistair Popple
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