From: Jason Gunthorpe <jgg@ziepe.ca>
To: Logan Gunthorpe <logang@deltatee.com>
Cc: linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
linux-block@vger.kernel.org, linux-pci@vger.kernel.org,
linux-mm@kvack.org, "Christoph Hellwig" <hch@lst.de>,
"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
"Dan Williams" <dan.j.williams@intel.com>,
"Christian König" <christian.koenig@amd.com>,
"John Hubbard" <jhubbard@nvidia.com>,
"Don Dutile" <ddutile@redhat.com>,
"Matthew Wilcox" <willy@infradead.org>,
"Daniel Vetter" <daniel.vetter@ffwll.ch>,
"Minturn Dave B" <dave.b.minturn@intel.com>,
"Jason Ekstrand" <jason@jlekstrand.net>,
"Dave Hansen" <dave.hansen@linux.intel.com>,
"Xiong Jianxin" <jianxin.xiong@intel.com>,
"Bjorn Helgaas" <helgaas@kernel.org>,
"Ira Weiny" <ira.weiny@intel.com>,
"Robin Murphy" <robin.murphy@arm.com>,
"Martin Oliveira" <martin.oliveira@eideticom.com>,
"Chaitanya Kulkarni" <ckulkarnilinux@gmail.com>,
"Ralph Campbell" <rcampbell@nvidia.com>,
"Stephen Bates" <sbates@raithlin.com>
Subject: Re: [PATCH v10 1/8] mm: introduce FOLL_PCI_P2PDMA to gate getting PCI P2PDMA pages
Date: Mon, 26 Sep 2022 19:57:14 -0300 [thread overview]
Message-ID: <YzIuSsFpOC+VN1/P@ziepe.ca> (raw)
In-Reply-To: <980899e1-532a-772b-2f6d-6fb017def50b@deltatee.com>
On Fri, Sep 23, 2022 at 05:51:49PM -0600, Logan Gunthorpe wrote:
> And on further consideration I really think the correct error return is
> important here. This will be a user facing error that'll be easy enough
> to hit: think code that might be run on any file and if the file is
> hosted on a block device that doesn't support P2PDMA then the user
> will see the very uninformative "Cannot allocate memory" error.
>
> Userspace code that's written for purpose can look at the EREMOTEIO error
> and tell the user something useful, if we return the correct error.
> If we return ENOMEM in this case, that is not possible because
> lots of things might have caused that error.
That is reasonable, but I'd still prefer to see it done more
centrally.
>> If we know PIN/GET is not set then we don't even need to call the
>> function because it is a NOP.
> That's not what the documentation for the function says:
> "Either FOLL_PIN or FOLL_GET (or neither) may be set... Return: true for success,
> or if no action was required (if neither FOLL_PIN nor FOLL_GET was set, nothing
> is done)."
I mean the way the code is structured is at the top of the call chain
the PIN/GET/0 is decided and then the callchain is run. All the
callsites of try_grab_page() must be safe to call under FOLL_PIN
because their caller is making the decision what flag to use.
Jason
next prev parent reply other threads:[~2022-09-26 22:57 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-22 16:39 [PATCH v10 0/8] Userspace P2PDMA with O_DIRECT NVMe devices Logan Gunthorpe
2022-09-22 16:39 ` [PATCH v10 1/8] mm: introduce FOLL_PCI_P2PDMA to gate getting PCI P2PDMA pages Logan Gunthorpe
2022-09-23 18:13 ` Jason Gunthorpe
2022-09-23 19:08 ` Logan Gunthorpe
2022-09-23 19:53 ` Jason Gunthorpe
2022-09-23 20:11 ` Logan Gunthorpe
2022-09-23 22:58 ` Jason Gunthorpe
2022-09-23 23:01 ` Logan Gunthorpe
2022-09-23 23:07 ` Jason Gunthorpe
2022-09-23 23:14 ` Logan Gunthorpe
2022-09-23 23:21 ` Jason Gunthorpe
2022-09-23 23:35 ` Logan Gunthorpe
2022-09-23 23:51 ` Logan Gunthorpe
2022-09-26 22:57 ` Jason Gunthorpe [this message]
2022-09-28 21:38 ` Logan Gunthorpe
2022-09-22 16:39 ` [PATCH v10 2/8] iov_iter: introduce iov_iter_get_pages_[alloc_]flags() Logan Gunthorpe
2022-09-22 16:39 ` [PATCH v10 3/8] block: add check when merging zone device pages Logan Gunthorpe
2022-09-22 16:39 ` [PATCH v10 4/8] lib/scatterlist: " Logan Gunthorpe
2022-09-22 16:39 ` [PATCH v10 5/8] block: set FOLL_PCI_P2PDMA in __bio_iov_iter_get_pages() Logan Gunthorpe
2022-09-22 16:39 ` [PATCH v10 6/8] block: set FOLL_PCI_P2PDMA in bio_map_user_iov() Logan Gunthorpe
2022-09-22 16:39 ` [PATCH v10 7/8] PCI/P2PDMA: Allow userspace VMA allocations through sysfs Logan Gunthorpe
2022-09-22 18:27 ` Bjorn Helgaas
2022-09-23 8:15 ` Greg Kroah-Hartman
2022-09-22 16:39 ` [PATCH v10 8/8] ABI: sysfs-bus-pci: add documentation for p2pmem allocate Logan Gunthorpe
2022-09-23 8:15 ` Greg Kroah-Hartman
2022-09-23 6:01 ` [PATCH v10 0/8] Userspace P2PDMA with O_DIRECT NVMe devices Christoph Hellwig
2022-09-23 15:25 ` Logan Gunthorpe
2022-09-23 8:16 ` Greg Kroah-Hartman
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