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.
Let's provide a flag (MEMHP_MERGE_RESOURCE) to specify that a resource
either created within add_memory*() or passed via add_memory_resource()
shall be marked mergeable and merged with applicable siblings.
To implement that, we need a kernel/resource interface to mark selected
System RAM resources mergeable (IORESOURCE_SYSRAM_MERGEABLE) and trigger
merging.
Note: We really want to merge after the whole operation succeeded, not
directly when adding a resource to the resource tree (it would break
add_memory_resource() and require splitting resources again when the
operation failed - e.g., due to -ENOMEM).
Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
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: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>
Cc: Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>
Cc: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
Cc: Wei Liu <wei.liu@xxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Cc: Julien Grall <julien@xxxxxxx>
Cc: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Wei Yang <richardw.yang@xxxxxxxxxxxxxxx>
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
include/linux/ioport.h | 4 +++
include/linux/memory_hotplug.h | 7 ++++
kernel/resource.c | 60 ++++++++++++++++++++++++++++++++++
mm/memory_hotplug.c | 7 ++++
4 files changed, 78 insertions(+)
diff --git a/include/linux/ioport.h b/include/linux/ioport.h
index d7620d7c941a0..7e61389dcb017 100644
--- a/include/linux/ioport.h
+++ b/include/linux/ioport.h
@@ -60,6 +60,7 @@ struct resource {
/* IORESOURCE_SYSRAM specific bits. */
#define IORESOURCE_SYSRAM_DRIVER_MANAGED 0x02000000 /* Always detected via a driver. */
+#define IORESOURCE_SYSRAM_MERGEABLE 0x04000000 /* Resource can be merged. */
#define IORESOURCE_EXCLUSIVE 0x08000000 /* Userland may not map this resource */
@@ -253,6 +254,9 @@ extern void __release_region(struct resource *, resource_size_t,
extern void release_mem_region_adjustable(struct resource *, resource_size_t,
resource_size_t);
#endif
+#ifdef CONFIG_MEMORY_HOTPLUG
+extern void merge_system_ram_resource(struct resource *res);
+#endif
/* Wrappers for managed devices */
struct device;
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 33eb80fdba22f..d65c6fdc5cfc3 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -62,6 +62,13 @@ typedef int __bitwise mhp_t;
/* No special request */
#define MHP_NONE ((__force mhp_t)0)
+/*
+ * Allow merging of the added System RAM resource with adjacent,
+ * mergeable resources. After a successful call to add_memory_resource()
+ * with this flag set, the resource pointer must no longer be used as it
+ * might be stale, or the resource might have changed.
+ */
+#define MEMHP_MERGE_RESOURCE ((__force mhp_t)BIT(0))
/*
* Extended parameters for memory hotplug:
diff --git a/kernel/resource.c b/kernel/resource.c
index 36b3552210120..7a91b935f4c20 100644
--- a/kernel/resource.c
+++ b/kernel/resource.c
@@ -1363,6 +1363,66 @@ void release_mem_region_adjustable(struct resource *parent,
}
#endif /* CONFIG_MEMORY_HOTREMOVE */
+#ifdef CONFIG_MEMORY_HOTPLUG
+static bool system_ram_resources_mergeable(struct resource *r1,
+ struct resource *r2)
+{
+ /* We assume either r1 or r2 is IORESOURCE_SYSRAM_MERGEABLE. */
+ return r1->flags == r2->flags && r1->end + 1 == r2->start &&
+ r1->name == r2->name && r1->desc == r2->desc &&
+ !r1->child && !r2->child;
+}
+
+/*
+ * merge_system_ram_resource - mark the System RAM resource mergeable and try to
+ * merge it with adjacent, mergeable resources
+ * @res: resource descriptor
+ *
+ * This interface is intended for memory hotplug, whereby lots of contiguous
+ * system ram resources are added (e.g., via add_memory*()) by a driver, and
+ * the actual resource boundaries are not of interest (e.g., it might be
+ * relevant for DIMMs). Only resources that are marked mergeable, that have the
+ * same parent, and that don't have any children are considered. All mergeable
+ * resources must be immutable during the request.
+ *
+ * Note:
+ * - The caller has to make sure that no pointers to resources that are
+ * marked mergeable are used anymore after this call - the resource might
+ * be freed and the pointer might be stale!
+ * - release_mem_region_adjustable() will split on demand on memory hotunplug
+ */
+void merge_system_ram_resource(struct resource *res)
+{
+ const unsigned long flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
+ struct resource *cur;
+
+ if (WARN_ON_ONCE((res->flags & flags) != flags))
+ return;
+
+ write_lock(&resource_lock);
+ res->flags |= IORESOURCE_SYSRAM_MERGEABLE;
+
+ /* Try to merge with next item in the list. */
+ cur = res->sibling;
+ if (cur && system_ram_resources_mergeable(res, cur)) {
+ res->end = cur->end;
+ res->sibling = cur->sibling;
+ free_resource(cur);
+ }
+
+ /* Try to merge with previous item in the list. */
+ cur = res->parent->child;
+ while (cur && cur->sibling != res)
+ cur = cur->sibling;
+ if (cur && system_ram_resources_mergeable(cur, res)) {
+ cur->end = res->end;
+ cur->sibling = res->sibling;
+ free_resource(res);
+ }
+ write_unlock(&resource_lock);
+}
+#endif /* CONFIG_MEMORY_HOTPLUG */
+
/*
* Managed region resource
*/
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 8f0bd7c9a63a5..553c718226b3e 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1102,6 +1102,13 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
/* device_online() will take the lock when calling online_pages() */
mem_hotplug_done();
+ /*
+ * In case we're allowed to merge the resource, flag it and trigger
+ * merging now that adding succeeded.
+ */
+ if (mhp_flags & MEMHP_MERGE_RESOURCE)
+ merge_system_ram_resource(res);
+
/* online pages if requested */
if (memhp_default_online_type != MMOP_OFFLINE)
walk_memory_blocks(start, size, NULL, online_memory_block);
--
2.26.2
