This is the follow-up of "[PATCH RFCv1 0/5] mm/memory_hotplug: selective merging of memory resources" [1] Some add_memory*() users add memory in small, contiguous memory blocks. Examples include virtio-mem, hyper-v balloon, and the XEN balloon. This can quickly result in a lot of memory resources, whereby the actual resource boundaries are not of interest (e.g., it might be relevant for DIMMs, exposed via /proc/iomem to user space). We really want to merge added resources in this scenario where possible. Resources are effectively stored in a list-based tree. Having a lot of resources not only wastes memory, it also makes traversing that tree more expensive, and makes /proc/iomem explode in size (e.g., requiring kexec-tools to manually merge resources when creating a kdump header. The current kexec-tools resource count limit does not allow for more than ~100GB of memory with a memory block size of 128MB on x86-64). Let's allow to selectively merge system ram resources directly below a specific parent resource. Patch #3 contains a /proc/iomem example. Only tested with virtio-mem. Note: This gets the job done and is comparably simple. More complicated approaches would require introducing IORESOURCE_MERGEABLE and extending our add_memory*() interfaces with a flag, specifying that merging after adding succeeded is acceptable. I'd like to avoid that complexity and code churn for now. [1] https://lkml.kernel.org/r/20200731091838.7490-1-david@xxxxxxxxxx RFC -> v1: - Switch from rather generic "merge_child_mem_resources()" where a resource name has to be specified to "merge_system_ram_resources(). - Smaller comment/documentation/patch description changes/fixes David Hildenbrand (5): kernel/resource: make release_mem_region_adjustable() never fail kernel/resource: merge_system_ram_resources() to merge resources after hotplug virtio-mem: try to merge system ram resources xen/balloon: try to merge system ram resources hv_balloon: try to merge system ram resources drivers/hv/hv_balloon.c | 3 ++ drivers/virtio/virtio_mem.c | 14 ++++- drivers/xen/balloon.c | 4 ++ include/linux/ioport.h | 7 ++- kernel/resource.c | 101 ++++++++++++++++++++++++++++-------- mm/memory_hotplug.c | 22 +------- 6 files changed, 105 insertions(+), 46 deletions(-) -- 2.26.2
