| Message ID | 20181013050021.11962-1-pagupta@redhat.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | kvm "fake DAX" device | expand |
On Fri, Oct 12, 2018 at 10:00 PM Pankaj Gupta <pagupta@redhat.com> wrote: > > This patch series has implementation for "fake DAX". > "fake DAX" is fake persistent memory(nvdimm) in guest > which allows to bypass the guest page cache. This also > implements a VIRTIO based asynchronous flush mechanism. Can we stop calling this 'fake DAX', because it isn't 'DAX' and it's starting to confuse people. This enabling is effectively a host-page-cache-passthrough mechanism not DAX. Let's call the whole approach virtio-pmem, and leave DAX out of the name to hopefully prevent people from wondering why some DAX features are disabled with this driver. For example MAP_SYNC is not compatible with this approach. Additional enabling is need to disable MAP_SYNC in the presence of a virtio-pmem device. See the rough proposal here: https://lkml.org/lkml/2018/4/25/756
> > > > This patch series has implementation for "fake DAX". > > "fake DAX" is fake persistent memory(nvdimm) in guest > > which allows to bypass the guest page cache. This also > > implements a VIRTIO based asynchronous flush mechanism. > > Can we stop calling this 'fake DAX', because it isn't 'DAX' and it's > starting to confuse people. This enabling is effectively a > host-page-cache-passthrough mechanism not DAX. Let's call the whole > approach virtio-pmem, and leave DAX out of the name to hopefully > prevent people from wondering why some DAX features are disabled with > this driver. For example MAP_SYNC is not compatible with this > approach. Sure. I got your point. I will use "virtio-pmem" in future. > > Additional enabling is need to disable MAP_SYNC in the presence of a > virtio-pmem device. See the rough proposal here: > > https://lkml.org/lkml/2018/4/25/756 Yes, I will handle disabling of MAP_SYNC for this use-case. Thanks, Pankaj
This patch series has implementation for "fake DAX". "fake DAX" is fake persistent memory(nvdimm) in guest which allows to bypass the guest page cache. This also implements a VIRTIO based asynchronous flush mechanism. Sharing guest kernel driver in this patchset with the changes suggested in v1. Tested with Qemu side device emulation for virtio-pmem [4]. Details of project idea for 'fake DAX' flushing interface is shared [2] & [3]. Implementation is divided into two parts: New virtio pmem guest driver and qemu code changes for new virtio pmem paravirtualized device. 1. Guest virtio-pmem kernel driver --------------------------------- - Reads persistent memory range from paravirt device and registers with 'nvdimm_bus'. - 'nvdimm/pmem' driver uses this information to allocate persistent memory region and setup filesystem operations to the allocated memory. - virtio pmem driver implements asynchronous flushing interface to flush from guest to host. 2. Qemu virtio-pmem device --------------------------------- - Creates virtio pmem device and exposes a memory range to KVM guest. - At host side this is file backed memory which acts as persistent memory. - Qemu side flush uses aio thread pool API's and virtio for asynchronous guest multi request handling. David Hildenbrand CCed also posted a modified version[5] of qemu virtio-pmem code based on updated Qemu memory device API. Virtio-pmem errors handling: ---------------------------------------- Checked behaviour of virtio-pmem for below types of errors Need suggestions on expected behaviour for handling these errors? - Hardware Errors: Uncorrectable recoverable Errors: a] virtio-pmem: - As per current logic if error page belongs to Qemu process, host MCE handler isolates(hwpoison) that page and send SIGBUS. Qemu SIGBUS handler injects exception to KVM guest. - KVM guest then isolates the page and send SIGBUS to guest userspace process which has mapped the page. b] Existing implementation for ACPI pmem driver: - Handles such errors with MCE notifier and creates a list of bad blocks. Read/direct access DAX operation return EIO if accessed memory page fall in bad block list. - It also starts backgound scrubbing. - Similar functionality can be reused in virtio-pmem with MCE notifier but without scrubbing(no ACPI/ARS)? Need inputs to confirm if this behaviour is ok or needs any change? Changes from PATCH v1: [1] - 0-day build test for build dependency on libnvdimm Changes suggested by - [Dan Williams] - Split the driver into two parts virtio & pmem - Move queuing of async block request to block layer - Add "sync" parameter in nvdimm_flush function - Use indirect call for nvdimm_flush - Don’t move declarations to common global header e.g nd.h - nvdimm_flush() return 0 or -EIO if it fails - Teach nsio_rw_bytes() that the flush can fail - Rename nvdimm_flush() to generic_nvdimm_flush() - Use 'nd_region->provider_data' for long dereferencing - Remove virtio_pmem_freeze/restore functions - Remove BSD license text with SPDX license text - Add might_sleep() in virtio_pmem_flush - [Luiz] - Make spin_lock_irqsave() narrow Changes from RFC v3 - Rebase to latest upstream - Luiz - Call ndregion->flush in place of nvdimm_flush- Luiz - kmalloc return check - Luiz - virtqueue full handling - Stefan - Don't map entire virtio_pmem_req to device - Stefan - request leak, correct sizeof req- Stefan - Move declaration to virtio_pmem.c Changes from RFC v2: - Add flush function in the nd_region in place of switching on a flag - Dan & Stefan - Add flush completion function with proper locking and wait for host side flush completion - Stefan & Dan - Keep userspace API in uapi header file - Stefan, MST - Use LE fields & New device id - MST - Indentation & spacing suggestions - MST & Eric - Remove extra header files & add licensing - Stefan Changes from RFC v1: - Reuse existing 'pmem' code for registering persistent memory and other operations instead of creating an entirely new block driver. - Use VIRTIO driver to register memory information with nvdimm_bus and create region_type accordingly. - Call VIRTIO flush from existing pmem driver. Pankaj Gupta (2): libnvdimm: nd_region flush callback support virtio-pmem: Add virtio-pmem guest driver [1] https://lkml.org/lkml/2018/8/31/407 [2] https://www.spinics.net/lists/kvm/msg149761.html [3] https://www.spinics.net/lists/kvm/msg153095.html [4] https://lkml.org/lkml/2018/8/31/413 [5] https://marc.info/?l=qemu-devel&m=153555721901824&w=2 drivers/acpi/nfit/core.c | 8 ++-- drivers/nvdimm/claim.c | 12 ++++-- drivers/nvdimm/nd.h | 2 + drivers/nvdimm/pmem.c | 24 +++++++++---- drivers/nvdimm/region_devs.c | 76 ++++++++++++++++++++++++++++++++++++++++--- include/linux/libnvdimm.h | 10 ++++- 6 files changed, 110 insertions(+), 22 deletions(-)