UMFS: An efficient user-space file system for non-volatile memory

Anisotropic behavior in the lithiation of a silicon nanopillar

“…In cases of SATA/IDE, the target system employs a hardware controller (i.e., disk controller) to manage their storage interface protocol, so the interface driver usually handles I/O interrupt or system memory management. In contrast, in the case of NVMe, a kernel module (NVMe driver) [11], [54], [55] Arrakis [14], [15], [16] Ishiguro et al [29] Aerie [17] RUMA [56] NVMeDirect [12] Moneta-D [20] Direct-FUSE [18] Strata [30] Breeze [57] Simurgh [25] XFUSE [58] SplitFS [21] HyCache [59] Quill [26] Son et al [60], [61] ZoFS [22] Davram [62] vNVML [27], [28] EvFS [19] Kuco [63] DLFS [64] URFS [65] UMFS [31] DevFS [23] CrossFS [24] FSP [32] directly accesses the PCIe bus over a memory mapped I/O and issues the request to the target SSD by composing an nvme_rw_command.…”

“…For these designs, kernel is responsible for control-plane operations. Other designs [23], [24], [31], [32], as shown in Figure 7, in contrast, only delegate few auxiliary responsibilities to the kernel. Namely, most frequently used functions (e.g., data read/write) are migrated to user space or device firmware while kernel serves as the auxiliary plane.…”

“…Kernel into the backstage. Considering that the kernel is still involved in most operations in current user-space file systems, Chen et al [31] presents a user-space file system design, named UMFS, to reduce the kernel's involvement. UMFS exploits a contiguous virtual memory space and hardware MMU to expose files directly to user space, and designs a new mechanism named user-space journaling to guarantee crash consistency.…”

“…Limiting kernel's involvement for kernel-bypass while still keeping the file system in kernel space, as in UMFS, can not fully reduce the overheads introduced by kernel. To address such defects, Kannan et al [23] proposes DevFS, which deserts aforementioned design ideas where file systems are kept in kernel space, such as kernel hiding in UMFS [31] and trusted server in Aerie [17]. DevFS takes a brave step forward by integrating device firmware into file system design and bypassing kernel for control-plane operations.…”

“…Other prior studies [14], [15], [16], [20], [25], [26], [27], [28] consider to decouple the memory management and the system software such that the address translation and boundary check can be served directly from the user space. Furthermore, there are also multiple new designs of file systems [17], [18], [19], [21], [22], [23], [24], [29], [30], [31], [32] to minimize the involvement of kernel in the file accesses. These work propose to construct user-space file systems, which can take over the tasks of the traditional file system.…”