Commit ec62d04e authored by David Hildenbrand's avatar David Hildenbrand Committed by Linus Torvalds
Browse files

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@gmail.com: fix use of ternary condition in release_mem_region_adjustable]
  Link: https://lkml.kernel.org/r/20200922060748.2452056-1-natechancellor@gmail.com
  Link: https://github.com/ClangBuiltLinux/linux/issues/1159



Signed-off-by: default avatarDavid Hildenbrand <david@redhat.com>
Signed-off-by: default avatarNathan Chancellor <natechancellor@gmail.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kees Cook <keescook@chromium.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Wei Yang <richardw.yang@linux.intel.com>
Cc: Anton Blanchard <anton@ozlabs.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Dave Jiang <dave.jiang@intel.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Julien Grall <julien@xen.org>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Len Brown <lenb@kernel.org>
Cc: Leonardo Bras <leobras.c@gmail.com>
Cc: Libor Pechacek <lpechacek@suse.cz>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Nathan Lynch <nathanl@linux.ibm.com>
Cc: "Oliver O'Halloran" <oohall@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Pingfan Liu <kernelfans@gmail.com>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Cc: Roger Pau Monn <roger.pau@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Wei Liu <wei.liu@kernel.org>
Link: https://lkml.kernel.org/r/20200911103459.10306-2-david@redhat.com


Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent b30c5927

include/linux/ioport.h

+2 −2
Original line number Diff line number Diff line
@@ -248,7 +248,7 @@ extern struct resource * __request_region(struct resource *, 
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,

extern void release_mem_region_adjustable(struct resource *, resource_size_t,

					  resource_size_t);

#endif

kernel/resource.c

+28 −21
Original line number Diff line number Diff line
@@ -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,

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 resource *parent, 
		 * 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 resource *parent, 
			/* 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 resource *parent, 
			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 resource *parent, 


	write_unlock(&resource_lock);

	free_resource(new_res);

	return ret;

}

#endif	/* CONFIG_MEMORY_HOTREMOVE */

mm/memory_hotplug.c

+1 −21
Original line number Diff line number Diff line
@@ -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 nid, u64 start, u64 size) 
		memblock_remove(start, size);

	}



	__release_memory_resource(start, size);

	release_mem_region_adjustable(&iomem_resource, start, size);



	try_offline_node(nid);

CRA Git | Maintained and supported by SUSTech CRA and CCSE