Cong Wang, who is responsible for the traffic control subsystem in the Linux kernel and is developing the Multikernel project, has introduced a new filesystem, DAXFS, to the list of Linux kernel developers. DAXFS utilizes RAM for data storage, operates in read-only mode, and resembles the functionality of trimmed-down filesystems ramfs and tmpfs. The kernel module implementing DAXFS and the mkdaxfs utility for creating the filesystem have been published under the GPLv2 license. Following a review, the possibility of integrating DAXFS into the main kernel composition will be considered.
A key feature of the new filesystem is the use of the DAX (Direct Access) subsystem to bypass the page cache and directly access shared physical memory. In ramfs and tmpfs, the contents are stored in the page cache, which, when using a filesystem in multiple containers or kernels launched using the Multikernel technology, leads to multiple copies of data being placed in physical memory. Filling ramfs and tmpfs also requires performing unnecessary copy operations without the possibility of mapping an existing memory area.
Direct memory access in DAXFS allows for the elimination of unnecessary copy operations and facilitates operation outside the traditional input/output stack based on block devices and buffering mechanisms, as well as avoids memory fragmentation when sharing one filesystem across different containers and multikernel kernels. DAXFS operates in Zero-Copy mode and directly delivers the content of files from memory without unnecessary data duplication in the page cache, with the possibility of mapping continuous areas of physical memory into each instance of the container or kernel. Additionally, the use of the dma-buf API for using memory exported by GPU, FPGA/SmartNIC, or CXL devices is supported.
The filesystem operates in read-only mode and is initialized by loading a pre-prepared image of the filesystem into memory, which simplifies implementation, eliminates the need for memory allocation operations during operation, and avoids complicated device management mechanisms.
DAXFS-i peamine rakendusala on kasutamine koos Multikernel tehnoloogiaga, mis võimaldab ühel füüsilisel arvutil käitada mitut sõltumatut Linuxi tuuma, millel on otsene juurdepääs riistvarainele ja mis võivad olla kasutusel mitmete isoleeritud süsteemi keskkondade käitamiseks.
DAXFS-i saab kasutada ka mitme konteineri või tuuma ühise juurdepääsu korraldamiseks põhisisu pildile, mis on paigaldatud jagatud mällu; riistvara kiirendite mälule juurdepääsu kulude vähendamiseks; mälule juurdepääsu organiseerimiseks mitmest hostist ilma võrgu sisend-väljundita või püsivale mällu juurdepääsuks CXL (Compute Express Link) baasil seadmetele.
Allikas: opennet.ru
