On 13.07.23 17:15, Verma, Vishal L wrote:
On Thu, 2023-07-13 at 09:23 +0200, David Hildenbrand wrote:
On 13.07.23 08:45, Verma, Vishal L wrote:
I'm taking a shot at implementing the splitting internally in
memory_hotplug.c. The caller (kmem) side does become trivial with this
approach, but there's a slight complication if I don't have the module
param override (patch 1 of this series).
The kmem diff now looks like:
diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index 898ca9505754..8be932f63f90 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -105,6 +105,8 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
data->mgid = rc;
for (i = 0; i < dev_dax->nr_range; i++) {
+ mhp_t mhp_flags = MHP_NID_IS_MGID | MHP_MEMMAP_ON_MEMORY |
+ MHP_SPLIT_MEMBLOCKS;
struct resource *res;
struct range range;
@@ -141,7 +143,7 @@ static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
* this as RAM automatically.
*/
rc = add_memory_driver_managed(data->mgid, range.start,
- range_len(&range), kmem_name, MHP_NID_IS_MGID);
+ range_len(&range), kmem_name, mhp_flags);
if (rc) {
dev_warn(dev, "mapping%d: %#llx-%#llx memory add failed\n",
Why do we need the MHP_SPLIT_MEMBLOCKS?
I thought we still wanted either an opt-in or opt-out for the kmem
driver to be able to do memmap_on_memory, in case there were
performance implications or the lack of 1GiB PUDs. I haven't
implemented that yet, but I was thinking along the lines of a sysfs
knob exposed by kmem, that controls setting of this new
MHP_SPLIT_MEMBLOCKS flag.
Why is MHP_MEMMAP_ON_MEMORY not sufficient for that?
In add_memory_driver_managed(), if memmap_on_memory = 1 AND is effective for a
single memory block, you can simply split up internally, no?
Essentially in add_memory_resource() something like
if (mhp_flags & MHP_MEMMAP_ON_MEMORY &&
mhp_supports_memmap_on_memory(memory_block_size_bytes())) {
for (cur_start = start, cur_start < start + size;
cur_start += memory_block_size_bytes()) {
mhp_altmap.free = PHYS_PFN(memory_block_size_bytes());
mhp_altmap.base_pfn = PHYS_PFN(start);
params.altmap = &mhp_altmap;
ret = arch_add_memory(nid, start,
memory_block_size_bytes(), ¶ms);
if (ret < 0) ...
ret = create_memory_block_devices(start, memory_block_size_bytes(),
mhp_altmap.alloc, group);
if (ret) ...
}
} else {
/* old boring stuff */
}
Of course, doing it a bit cleaner, factoring out adding of mem+creating devices into
a helper so we can use it on the other path, avoiding repeating memory_block_size_bytes()
...
My current approach was looping a level higher, on the call to
add_memory_resource, but this looks reasonable too, and I can switch to
this. In fact it is better as in my case I had to loop twice, once for
the regular add_memory() path and once for the _driver_managed() path.
Yours should avoid that.
As we only care about the altmap here, handling it for arch_add_memory()
+ create_memory_block_devices() should be sufficient.
--
Cheers,
David / dhildenb
