hulk inclusion category: feature bugzilla: https://gitee.com/openeuler/release-management/issues/ID3TGE -------------------------------- Add documentation for zcopy driver module. Signed-off-by: Liu Mingrui <liumingrui@huawei.com> --- Documentation/misc-devices/zcopy.rst | 64 ++++++++++++++++++++++++++++ MAINTAINERS | 1 + 2 files changed, 65 insertions(+) create mode 100644 Documentation/misc-devices/zcopy.rst diff --git a/Documentation/misc-devices/zcopy.rst b/Documentation/misc-devices/zcopy.rst new file mode 100644 index 000000000000..20a4e43d2def --- /dev/null +++ b/Documentation/misc-devices/zcopy.rst @@ -0,0 +1,64 @@ +.. SPDX-License-Identifier: GPL-2.0 + +==================== +Kernel driver eeprom +==================== + + +Description +----------- +the PAGEATTACH mechanism, a zero-copy data transfer solution optimized for +High Performance Computing workloads. It allows direct sharing of physical +memory pages between distinct processes by mapping source pages to a target +address space, eliminating redundant data copying and improving large data +transfer efficiency. + + +Key features +----------- +- Supports zero-copy communication between intra-node processes. +- Handles both PTE-level small pages and PMD-level huge pages. +- Preserves the read/write permissions of the source page in the target address space. + + +Important constraints and requirements +--------------------- +1. Callers must ensure the source address is already mapped to physical pages, +while the destination address is unused (no existing mappings). If exists +old mappings, the return value is -EAGAIN. For this case, caller should free +the old dst_addr, and alloc a new one to try again. + +2. No internal locking is implemented in the PageAttach interface; Callers +must manage memory mapping and release order to avoid race conditions. + +3. Source and destination must be different processes (not threads of the same process). + +4. Only user-space addresses are supported; kernel addresses cannot be mapped. + +5. Both source and destination processes must remain alive during the mapping operation. + +6. PUD-level huge pages are not supported in current implementation. + +7. The start address and size of both source and destination must be PMD-size-aligned. + +8. Callers are responsible for ensuring safe access to mapped pages after attachment, +as permissions are inherited from the source. + + +Use +--- +Process a + src_addr= aligned_alloc(ALIGN_SIZE_2M, size); + memset(src_addr, 0, size); + +Process b + #define ALIGN_SIZE_2M 2097152 + int fd = open(SLS_DEVICE, O_RDWR); + + dst_addr= aligned_alloc(ALIGN_SIZE_2M, size); + res = zcopy(fd, (void *)src_addr, dst_addr, src_pid, dst_pid, size); + while(res.ret == -EAGAIN && retry--) { + free(dst_addr); + dst_addr= aligned_alloc(ALIGN_SIZE_2M, size); + res = zcopy(fd, (void *)src_addr, dst_addr, src_pid, dst_pid, aligned_size); + } diff --git a/MAINTAINERS b/MAINTAINERS index 3b402b41ee63..4fb57819c0c8 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -19652,6 +19652,7 @@ F: mm/zswap.c ZCOPY DRIVER M: Mingrui Liu <liumingrui@huawei.com> S: Maintained +F: Documentation/misc-devices/zcopy.rst F: drivers/zcopy/ F: include/trace/events/attach.h -- 2.25.1