On 08/06/2018 08:52 AM, Rashmica Gupta wrote: > When hot-removing memory release_mem_region_adjustable() splits > iomem resources if they are not the exact size of the memory being > hot-deleted. Adding this memory back to the kernel adds a new > resource. > > Eg a node has memory 0x0 - 0xfffffffff. Offlining and hot-removing > 1GB from 0xf40000000 results in the single resource 0x0-0xfffffffff being > split into two resources: 0x0-0xf3fffffff and 0xf80000000-0xfffffffff. > > When we hot-add the memory back we now have three resources: > 0x0-0xf3fffffff, 0xf40000000-0xf7fffffff, and 0xf80000000-0xfffffffff. > > Now if we try to remove a section of memory that overlaps these resources, > like 2GB from 0xf40000000, release_mem_region_adjustable() fails as it > expects the chunk of memory to be within the boundaries of a single > resource.
Hi, it's the first time I see the resource code, so I might be easily wrong. How can it happen that the second remove is section aligned but the first one not? > This patch adds a function request_resource_and_merge(). This is called > instead of request_resource_conflict() when registering a resource in > add_memory(). It calls request_resource_conflict() and if hot-removing is > enabled (if it isn't we won't get resource fragmentation) we attempt to > merge contiguous resources on the node. > > Signed-off-by: Rashmica Gupta <[email protected]> ... > --- a/kernel/resource.c > +++ b/kernel/resource.c ... > +/* > + * Attempt to merge resources on the node > + */ > +static void merge_node_resources(int nid, struct resource *parent) > +{ > + struct resource *res; > + uint64_t start_addr; > + uint64_t end_addr; > + int ret; > + > + start_addr = node_start_pfn(nid) << PAGE_SHIFT; > + end_addr = node_end_pfn(nid) << PAGE_SHIFT; > + > + write_lock(&resource_lock); > + > + /* Get the first resource */ > + res = parent->child; > + > + while (res) { > + /* Check that the resource is within the node */ > + if (res->start < start_addr) { > + res = res->sibling; > + continue; > + } > + /* Exit if resource is past end of node */ > + if (res->sibling->end > end_addr) > + break; IIUC, resource end is closed, so adjacent resources's start is end+1. But node_end_pfn is open, so the comparison above should use '>=' instead of '>'? > + > + ret = merge_resources(res); > + if (!ret) > + continue; > + res = res->sibling; Should this rather use next_resource() to merge at all levels of the hierarchy? Although memory seems to be flat under &iomem_resource so it would be just future-proofing. Thanks, Vlastimil
