On 2021/2/9 17:37, Greg KH wrote: > 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@xxxxxxxxxxxxx> 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 :) manpage is maintained in another repo. Do you mean add a manpage patch in this series? Best, Zhou > > thanks, > > greg k-h > > . >
