Hi All, This is V2 of the patches. I had posted V1 here. https://lore.kernel.org/linux-fsdevel/20200304165845.3081-1-vgoyal@xxxxxxxxxx/ I have taken care of most of the comments from V1. Amir had suggested that some of the code can be moved to a new file, may be post series. I have left that item for the post series cleanup. Miklos was concerned about KVM error handling when a mapped file on host gets truncated and guest tries to access it. As of now guest can spin in infinite loop. I have tried to address that with KVM developers and there is no easy race free way to inject synchronous exception which can indicate error in guest. For now, I have proposed that atleast guest can exit to qemu with error when such scenario happen and proposed a patch which has got two acks. But it has not been merged yet. https://lore.kernel.org/kvm/20200720211359.GF502563@xxxxxxxxxx/ We don't support modifications in virtiofs files from host or from other guests. And even if somebody modifies it, qemu will exit gracefully without bringing down host. So I think this probably is good enough for now to make progress on virtiofs DAX patches. Fixing kvm to inject errors is not easy and is a complicated design. We will need to make sure that happens before we support DAX in shared mode in virtiofs. But blocking behind this is proabably not a good idea because DAX can be very useful in non-shared mode in kata containers. Performance numbers are more or less same as in V1 post. So I am not providing any numbers again. In general, DAX can provide a good performance boost and memory savings. Any thoughts or feedback is welcome. Description from previous post ------------------------------ This patch series adds DAX support to virtiofs filesystem. This allows bypassing guest page cache and allows mapping host page cache directly in guest address space. When a page of file is needed, guest sends a request to map that page (in host page cache) in qemu address space. Inside guest this is a physical memory range controlled by virtiofs device. And guest directly maps this physical address range using DAX and hence gets access to file data on host. This can speed up things considerably in many situations. Also this can result in substantial memory savings as file data does not have to be copied in guest and it is directly accessed from host page cache. Most of the changes are limited to fuse/virtiofs. There are couple of changes needed in generic dax infrastructure and couple of changes in virtio to be able to access shared memory region. Thanks Vivek Sebastien Boeuf (3): virtio: Add get_shm_region method virtio: Implement get_shm_region for PCI transport virtio: Implement get_shm_region for MMIO transport Stefan Hajnoczi (2): virtio_fs, dax: Set up virtio_fs dax_device fuse,dax: add DAX mmap support Vivek Goyal (15): dax: Modify bdev_dax_pgoff() to handle NULL bdev dax: Create a range version of dax_layout_busy_page() virtiofs: Provide a helper function for virtqueue initialization fuse: Get rid of no_mount_options fuse,virtiofs: Add a mount option to enable dax fuse,virtiofs: Keep a list of free dax memory ranges fuse: implement FUSE_INIT map_alignment field fuse: Introduce setupmapping/removemapping commands fuse, dax: Implement dax read/write operations fuse, dax: Take ->i_mmap_sem lock during dax page fault fuse,virtiofs: Define dax address space operations fuse,virtiofs: Maintain a list of busy elements fuse: Release file in process context fuse: Take inode lock for dax inode truncation fuse,virtiofs: Add logic to free up a memory range drivers/dax/super.c | 3 +- drivers/virtio/virtio_mmio.c | 32 + drivers/virtio/virtio_pci_modern.c | 96 +++ fs/dax.c | 66 +- fs/fuse/dir.c | 2 + fs/fuse/file.c | 1189 +++++++++++++++++++++++++++- fs/fuse/fuse_i.h | 112 ++- fs/fuse/inode.c | 147 +++- fs/fuse/virtio_fs.c | 279 ++++++- include/linux/dax.h | 6 + include/linux/virtio_config.h | 17 + include/uapi/linux/fuse.h | 34 +- include/uapi/linux/virtio_fs.h | 3 + include/uapi/linux/virtio_mmio.h | 11 + include/uapi/linux/virtio_pci.h | 11 +- 15 files changed, 1927 insertions(+), 81 deletions(-) -- 2.25.4
