From: Greg KH <gregkh@linuxfoundation.org>
To: Zhou Wang <wangzhou1@hisilicon.com>
Cc: jean-philippe@linaro.org, kevin.tian@intel.com,
Sihang Chen <chensihang1@hisilicon.com>,
jgg@ziepe.ca, linux-api@vger.kernel.org,
linux-kernel@vger.kernel.org,
Andy Lutomirski <luto@amacapital.net>,
linux-mm@kvack.org, iommu@lists.linux-foundation.org,
Alexander Viro <viro@zeniv.linux.org.uk>,
zhangfei.gao@linaro.org,
Andrew Morton <akpm@linux-foundation.org>,
liguozhu@hisilicon.com, linux-arm-kernel@lists.infradead.org
Subject: Re: [RFC PATCH v3 1/2] mempinfd: Add new syscall to provide memory pin
Date: Tue, 9 Feb 2021 10:37:45 +0100 [thread overview]
Message-ID: <YCJX6QFQ4hsNRrFj@kroah.com> (raw)
In-Reply-To: <2e6cf99f-beb6-9bef-1316-5e58fb0aa86e@hisilicon.com>
On Tue, Feb 09, 2021 at 05:17:46PM +0800, Zhou Wang wrote:
> On 2021/2/8 6:02, Andy Lutomirski wrote:
> >
> >
> >> On Feb 7, 2021, at 12:31 AM, Zhou Wang <wangzhou1@hisilicon.com> wrote:
> >>
> >> SVA(share virtual address) offers a way for device to share process virtual
> >> address space safely, which makes more convenient for user space device
> >> driver coding. However, IO page faults may happen when doing DMA
> >> operations. As the latency of IO page fault is relatively big, DMA
> >> performance will be affected severely when there are IO page faults.
> >> From a long term view, DMA performance will be not stable.
> >>
> >> In high-performance I/O cases, accelerators might want to perform
> >> I/O on a memory without IO page faults which can result in dramatically
> >> increased latency. Current memory related APIs could not achieve this
> >> requirement, e.g. mlock can only avoid memory to swap to backup device,
> >> page migration can still trigger IO page fault.
> >>
> >> Various drivers working under traditional non-SVA mode are using
> >> their own specific ioctl to do pin. Such ioctl can be seen in v4l2,
> >> gpu, infiniband, media, vfio, etc. Drivers are usually doing dma
> >> mapping while doing pin.
> >>
> >> But, in SVA mode, pin could be a common need which isn't necessarily
> >> bound with any drivers, and neither is dma mapping needed by drivers
> >> since devices are using the virtual address of CPU. Thus, It is better
> >> to introduce a new common syscall for it.
> >>
> >> This patch leverages the design of userfaultfd and adds mempinfd for pin
> >> to avoid messing up mm_struct. A fd will be got by mempinfd, then user
> >> space can do pin/unpin pages by ioctls of this fd, all pinned pages under
> >> one file will be unpinned in file release process. Like pin page cases in
> >> other places, can_do_mlock is used to check permission and input
> >> parameters.
> >
> >
> > Can you document what the syscall does?
>
> Will add related document in Documentation/vm.
A manpage is always good, and will be required eventually :)
thanks,
greg k-h
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next prev parent reply other threads:[~2021-02-09 9:37 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-07 8:18 [RFC PATCH v3 0/2] mempinfd: Add new syscall to provide memory pin Zhou Wang
2021-02-07 8:18 ` [RFC PATCH v3 1/2] " Zhou Wang
2021-02-07 21:34 ` Matthew Wilcox
2021-02-07 22:24 ` Song Bao Hua (Barry Song)
2021-02-08 1:30 ` Matthew Wilcox
2021-02-08 2:27 ` Song Bao Hua (Barry Song)
2021-02-08 8:21 ` David Hildenbrand
2021-02-08 10:13 ` Song Bao Hua (Barry Song)
2021-02-08 10:37 ` David Hildenbrand
2021-02-08 20:52 ` Song Bao Hua (Barry Song)
2021-02-08 2:18 ` David Rientjes via iommu
2021-02-08 5:34 ` Song Bao Hua (Barry Song)
2021-02-07 21:51 ` Arnd Bergmann
2021-02-09 9:27 ` Zhou Wang
2021-02-07 22:02 ` Andy Lutomirski
2021-02-09 9:17 ` Zhou Wang
2021-02-09 9:37 ` Greg KH [this message]
2021-02-09 11:58 ` Zhou Wang
2021-02-09 12:01 ` Greg KH
2021-02-09 12:20 ` Zhou Wang
2021-02-10 18:50 ` Matthew Wilcox
2021-02-08 8:14 ` David Hildenbrand
2021-02-08 18:33 ` Jason Gunthorpe
2021-02-08 20:35 ` Song Bao Hua (Barry Song)
2021-02-08 21:30 ` Jason Gunthorpe
2021-02-09 3:01 ` Song Bao Hua (Barry Song)
2021-02-09 13:53 ` Jason Gunthorpe
2021-02-09 22:22 ` Song Bao Hua (Barry Song)
2021-02-10 18:04 ` Jason Gunthorpe
2021-02-10 21:39 ` Song Bao Hua (Barry Song)
2021-02-11 10:28 ` David Hildenbrand
2021-02-07 8:18 ` [RFC PATCH v3 2/2] selftests/vm: add mempinfd test Zhou Wang
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