From: David Hildenbrand <david@xxxxxxxxxx> Subject: kernel/resource: make release_mem_region_adjustable() never fail Patch series "selective merging of system ram resources", v4. 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 by specifying a new flag for add_memory*(). Patch #5 contains a /proc/iomem example. Only tested with virtio-mem. This patch (of 8): Let's make sure splitting a resource on memory hotunplug will never fail. This will become more relevant once we merge selected System RAM resources - then, we'll trigger that case more often on memory hotunplug. In general, this function is already unlikely to fail. When we remove memory, we free up quite a lot of metadata (memmap, page tables, memory block device, etc.). The only reason it could really fail would be when injecting allocation errors. All other error cases inside release_mem_region_adjustable() seem to be sanity checks if the function would be abused in different context - let's add WARN_ON_ONCE() in these cases so we can catch them. [natechancellor@xxxxxxxxx: fix use of ternary condition in release_mem_region_adjustable] Link: https://lkml.kernel.org/r/20200922060748.2452056-1-natechancellor@xxxxxxxxx Link: https://github.com/ClangBuiltLinux/linux/issues/1159 Link: https://lkml.kernel.org/r/20200911103459.10306-2-david@xxxxxxxxxx Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> Signed-off-by: Nathan Chancellor <natechancellor@xxxxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: Jason Gunthorpe <jgg@xxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Ard Biesheuvel <ardb@xxxxxxxxxx> Cc: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx> Cc: Baoquan He <bhe@xxxxxxxxxx> Cc: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx> Cc: Anton Blanchard <anton@xxxxxxxxxx> Cc: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx> Cc: Dave Jiang <dave.jiang@xxxxxxxxx> Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx> Cc: Heiko Carstens <hca@xxxxxxxxxxxxx> Cc: Jason Wang <jasowang@xxxxxxxxxx> Cc: Juergen Gross <jgross@xxxxxxxx> Cc: Julien Grall <julien@xxxxxxx> Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx> Cc: Len Brown <lenb@xxxxxxxxxx> Cc: Leonardo Bras <leobras.c@xxxxxxxxx> Cc: Libor Pechacek <lpechacek@xxxxxxx> Cc: Michael Ellerman <mpe@xxxxxxxxxxxxxx> Cc: "Michael S. Tsirkin" <mst@xxxxxxxxxx> Cc: Nathan Lynch <nathanl@xxxxxxxxxxxxx> Cc: "Oliver O'Halloran" <oohall@xxxxxxxxx> Cc: Paul Mackerras <paulus@xxxxxxxxx> Cc: Pingfan Liu <kernelfans@xxxxxxxxx> Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx> Cc: Roger Pau Monn <roger.pau@xxxxxxxxxx> Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx> Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx> Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx> Cc: Wei Liu <wei.liu@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- include/linux/ioport.h | 4 +-- kernel/resource.c | 49 ++++++++++++++++++++++----------------- mm/memory_hotplug.c | 22 ----------------- 3 files changed, 31 insertions(+), 44 deletions(-) --- a/include/linux/ioport.h~kernel-resource-make-release_mem_region_adjustable-never-fail +++ a/include/linux/ioport.h @@ -248,8 +248,8 @@ extern struct resource * __request_regio extern void __release_region(struct resource *, resource_size_t, resource_size_t); #ifdef CONFIG_MEMORY_HOTREMOVE -extern int release_mem_region_adjustable(struct resource *, resource_size_t, - resource_size_t); +extern void release_mem_region_adjustable(struct resource *, resource_size_t, + resource_size_t); #endif /* Wrappers for managed devices */ --- a/kernel/resource.c~kernel-resource-make-release_mem_region_adjustable-never-fail +++ a/kernel/resource.c @@ -1258,21 +1258,28 @@ EXPORT_SYMBOL(__release_region); * assumes that all children remain in the lower address entry for * simplicity. Enhance this logic when necessary. */ -int release_mem_region_adjustable(struct resource *parent, - resource_size_t start, resource_size_t size) +void release_mem_region_adjustable(struct resource *parent, + resource_size_t start, resource_size_t size) { + struct resource *new_res = NULL; + bool alloc_nofail = false; struct resource **p; struct resource *res; - struct resource *new_res; resource_size_t end; - int ret = -EINVAL; end = start + size - 1; - if ((start < parent->start) || (end > parent->end)) - return ret; + if (WARN_ON_ONCE((start < parent->start) || (end > parent->end))) + return; - /* The alloc_resource() result gets checked later */ - new_res = alloc_resource(GFP_KERNEL); + /* + * We free up quite a lot of memory on memory hotunplug (esp., memap), + * just before releasing the region. This is highly unlikely to + * fail - let's play save and make it never fail as the caller cannot + * perform any error handling (e.g., trying to re-add memory will fail + * similarly). + */ +retry: + new_res = alloc_resource(GFP_KERNEL | (alloc_nofail ? __GFP_NOFAIL : 0)); p = &parent->child; write_lock(&resource_lock); @@ -1298,7 +1305,6 @@ int release_mem_region_adjustable(struct * so if we are dealing with them, let us just back off here. */ if (!(res->flags & IORESOURCE_SYSRAM)) { - ret = 0; break; } @@ -1315,20 +1321,23 @@ int release_mem_region_adjustable(struct /* free the whole entry */ *p = res->sibling; free_resource(res); - ret = 0; } else if (res->start == start && res->end != end) { /* adjust the start */ - ret = __adjust_resource(res, end + 1, - res->end - end); + WARN_ON_ONCE(__adjust_resource(res, end + 1, + res->end - end)); } else if (res->start != start && res->end == end) { /* adjust the end */ - ret = __adjust_resource(res, res->start, - start - res->start); + WARN_ON_ONCE(__adjust_resource(res, res->start, + start - res->start)); } else { - /* split into two entries */ + /* split into two entries - we need a new resource */ if (!new_res) { - ret = -ENOMEM; - break; + new_res = alloc_resource(GFP_ATOMIC); + if (!new_res) { + alloc_nofail = true; + write_unlock(&resource_lock); + goto retry; + } } new_res->name = res->name; new_res->start = end + 1; @@ -1339,9 +1348,8 @@ int release_mem_region_adjustable(struct new_res->sibling = res->sibling; new_res->child = NULL; - ret = __adjust_resource(res, res->start, - start - res->start); - if (ret) + if (WARN_ON_ONCE(__adjust_resource(res, res->start, + start - res->start))) break; res->sibling = new_res; new_res = NULL; @@ -1352,7 +1360,6 @@ int release_mem_region_adjustable(struct write_unlock(&resource_lock); free_resource(new_res); - return ret; } #endif /* CONFIG_MEMORY_HOTREMOVE */ --- a/mm/memory_hotplug.c~kernel-resource-make-release_mem_region_adjustable-never-fail +++ a/mm/memory_hotplug.c @@ -1727,26 +1727,6 @@ void try_offline_node(int nid) } EXPORT_SYMBOL(try_offline_node); -static void __release_memory_resource(resource_size_t start, - resource_size_t size) -{ - int ret; - - /* - * When removing memory in the same granularity as it was added, - * this function never fails. It might only fail if resources - * have to be adjusted or split. We'll ignore the error, as - * removing of memory cannot fail. - */ - ret = release_mem_region_adjustable(&iomem_resource, start, size); - if (ret) { - resource_size_t endres = start + size - 1; - - pr_warn("Unable to release resource <%pa-%pa> (%d)\n", - &start, &endres, ret); - } -} - static int __ref try_remove_memory(int nid, u64 start, u64 size) { int rc = 0; @@ -1780,7 +1760,7 @@ static int __ref try_remove_memory(int n memblock_remove(start, size); } - __release_memory_resource(start, size); + release_mem_region_adjustable(&iomem_resource, start, size); try_offline_node(nid); _
