Loading
RDMA/core: Acquire and release mmap_sem on page range
Currently mmap_sem is read locked while pinning the memory. In a multi-threaded application of a process, holding mmap_sem lock creates contention with other threads who might be either registering memory, creating QPs or simply doing mmap() as such operations also require to hold the mmap_sem write lock. All such operation cannot make forward progress until one memory pin operation is completed. It becomes more worse if the memory is unpinned and/or memory registration is large (in GB range). Therefore, instead of holding mmap_sem for too long (for whole region pinning), acquire and release the lock for every few pages. For example on x86 with 4K page size, acquire and release mmap_sem for every 2Mbytes memory chunk. This allows other competing threads to make progress who might wish to hold mmap_sem for shorter duration. When memory registration latency is measured using [1] for memory sizes ranging from 4K to 48GB, <= 1% or 0.5% degradation is noticed. In many runs no difference is seen other than run-to-run variance. In other targeted tests of users with large memory, desired improvements are seen due to reduced contention of mmap_sem. [1] https://github.com/paravmellanox/rtool $ rdma_resource_lat -c 1 -s 48G -a -u L -i 500 -A It registers pinned memory from 4K to 48GB size with 500 iterations for each memory size. $ rdma_resource_lat -c 1 -s 12G -a -u L -i 500 -t 4 4 competing threads pin memory, each of 12GB size with 500 iterations. Signed-off-by:Parav Pandit <parav@mellanox.com> Signed-off-by: