On 16.06.23 00:00, Vishal Verma wrote:
With DAX memory regions originating from CXL memory expanders or
NVDIMMs, the kmem driver may be hot-adding huge amounts of system memory
on a system without enough 'regular' main memory to support the memmap
for it. To avoid this, ensure that all kmem managed hotplugged memory is
added with the MHP_MEMMAP_ON_MEMORY flag to place the memmap on the
new memory region being hot added.
To do this, call add_memory() in chunks of memory_block_size_bytes() as
that is a requirement for memmap_on_memory. Additionally, Use the
mhp_flag to force the memmap_on_memory checks regardless of the
respective module parameter setting.
Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
Cc: Len Brown <lenb@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Signed-off-by: Vishal Verma <vishal.l.verma@xxxxxxxxx>
---
drivers/dax/kmem.c | 49 ++++++++++++++++++++++++++++++++++++-------------
1 file changed, 36 insertions(+), 13 deletions(-)
diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index 7b36db6f1cbd..0751346193ef 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -12,6 +12,7 @@
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/memory-tiers.h>
+#include <linux/memory_hotplug.h>
#include "dax-private.h"
#include "bus.h"
@@ -105,6 +106,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
data->mgid = rc;
for (i = 0; i < dev_dax->nr_range; i++) {
+ u64 cur_start, cur_len, remaining;
struct resource *res;
struct range range;
@@ -137,21 +139,42 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
res->flags = IORESOURCE_SYSTEM_RAM;
/*
- * Ensure that future kexec'd kernels will not treat
- * this as RAM automatically.
+ * Add memory in chunks of memory_block_size_bytes() so that
+ * it is considered for MHP_MEMMAP_ON_MEMORY
+ * @range has already been aligned to memory_block_size_bytes(),
+ * so the following loop will always break it down cleanly.
*/
- rc = add_memory_driver_managed(data->mgid, range.start,
- range_len(&range), kmem_name, MHP_NID_IS_MGID);
+ cur_start = range.start;
+ cur_len = memory_block_size_bytes();
+ remaining = range_len(&range);
+ while (remaining) {
+ mhp_t mhp_flags = MHP_NID_IS_MGID;
- if (rc) {
- dev_warn(dev, "mapping%d: %#llx-%#llx memory add failed\n",
- i, range.start, range.end);
- remove_resource(res);
- kfree(res);
- data->res[i] = NULL;
- if (mapped)
- continue;
- goto err_request_mem;
+ if (mhp_supports_memmap_on_memory(cur_len,
+ MHP_MEMMAP_ON_MEMORY))
+ mhp_flags |= MHP_MEMMAP_ON_MEMORY;
+ /*
+ * Ensure that future kexec'd kernels will not treat
+ * this as RAM automatically.
+ */
+ rc = add_memory_driver_managed(data->mgid, cur_start,
+ cur_len, kmem_name,
+ mhp_flags);
+
+ if (rc) {
+ dev_warn(dev,
+ "mapping%d: %#llx-%#llx memory add failed\n",
+ i, cur_start, cur_start + cur_len - 1);
+ remove_resource(res);
+ kfree(res);
+ data->res[i] = NULL;
+ if (mapped)
+ continue;
+ goto err_request_mem;
+ }
+
+ cur_start += cur_len;
+ remaining -= cur_len;
}
mapped++;
}
Maybe the better alternative is teach
add_memory_resource()/try_remove_memory() to do that internally.
In the add_memory_resource() case, it might be a loop around that
memmap_on_memory + arch_add_memory code path (well, and the error path
also needs adjustment):
/*
* Self hosted memmap array
*/
if (mhp_flags & MHP_MEMMAP_ON_MEMORY) {
if (!mhp_supports_memmap_on_memory(size)) {
ret = -EINVAL;
goto error;
}
mhp_altmap.free = PHYS_PFN(size);
mhp_altmap.base_pfn = PHYS_PFN(start);
params.altmap = &mhp_altmap;
}
/* call arch's memory hotadd */
ret = arch_add_memory(nid, start, size, ¶ms);
if (ret < 0)
goto error;
Note that we want to handle that on a per memory-block basis, because we
don't want the vmemmap of memory block #2 to end up on memory block #1.
It all gets messy with memory onlining/offlining etc otherwise ...
--
Cheers,
David / dhildenb
