The dax/kmem driver can potentially hot-add large amounts of memory
originating from CXL memory expanders, or NVDIMMs, or other 'device
memories'. There is a chance there isn't enough regular system memory
available to fit the memmap for this new memory. It's therefore
desirable, if all other conditions are met, for the kmem managed memory
to place its memmap on the newly added memory itself.
The main hurdle for accomplishing this for kmem is that memmap_on_memory
can only be done if the memory being added is equal to the size of one
memblock. To overcome this, allow the hotplug code to split an add_memory()
request into memblock-sized chunks, and try_remove_memory() to also
expect and handle such a scenario.
Patch 1 teaches the memory_hotplug code to allow for splitting
add_memory() and remove_memory() requests over memblock sized chunks.
Patch 2 adds a sysfs control for the kmem driver that would
allow an opt-out of using memmap_on_memory for the memory being added.
Signed-off-by: Vishal Verma <[email protected]>
---
Changes in v6:
- Add a prep patch to replace an open coded kmemdup in
add_memory_resource() (Dan Williams)
- Fix ordering of firmware_map_remove w.r.t taking the hotplug lock
(David Hildenbrand)
- Remove unused 'nid' variable, and a stray whitespace (David Hildenbrand)
- Clean up and simplify the altmap vs non-altmap paths for
try_remove_memory (David Hildenbrand)
- Add a note to the changelog in patch 1 linking to the PUD mappings
proposal (David Hildenbrand)
- Remove the new sysfs ABI from the kmem/dax drivers until ABI
documentation for /sys/bus/dax can be established (will split this out
into a separate patchset) (Dan Williams)
- Link to v5: https://lore.kernel.org/r/[email protected]
Changes in v5:
- Separate out per-memblock operations from per memory block operations
in try_remove_memory(), and rename the inner function appropriately.
This does expand the scope of the memory hotplug lock to include
remove_memory_block_devices(), but the alternative was to drop the
lock in the inner function separately for each iteration, and then
re-acquire it in try_remove_memory() creating a small window where
the lock isn't held. (David Hildenbrand)
- Remove unnecessary rc check from the memmap_on_memory_store sysfs
helper in patch 2 (Dan Carpenter)
- Link to v4: https://lore.kernel.org/r/[email protected]
Changes in v4:
- Rebase to Aneesh's PPC64 memmap_on_memory series v8 [2].
- Tweak a goto / error path in add_memory_create_devices() (Jonathan)
- Retain the old behavior for dax devices, only default to
memmap_on_memory for CXL (Jonathan)
- Link to v3: https://lore.kernel.org/r/[email protected]
[2]: https://lore.kernel.org/linux-mm/[email protected]
Changes in v3:
- Rebase on Aneesh's patches [1]
- Drop Patch 1 - it is not needed since [1] allows for dynamic setting
of the memmap_on_memory param (David)
- Link to v2: https://lore.kernel.org/r/[email protected]
[1]: https://lore.kernel.org/r/[email protected]
Changes in v2:
- Drop the patch to create an override path for the memmap_on_memory
module param (David)
- Move the chunking into memory_hotplug.c so that any caller of
add_memory() can request this behavior. (David)
- Handle remove_memory() too. (David, Ying)
- Add a sysfs control in the kmem driver for memmap_on_memory semantics
(David, Jonathan)
- Add a #else case to define mhp_supports_memmap_on_memory() if
CONFIG_MEMORY_HOTPLUG is unset. (0day report)
- Link to v1: https://lore.kernel.org/r/[email protected]
---
Vishal Verma (3):
mm/memory_hotplug: replace an open-coded kmemdup() in add_memory_resource()
mm/memory_hotplug: split memmap_on_memory requests across memblocks
dax/kmem: allow kmem to add memory with memmap_on_memory
drivers/dax/bus.h | 1 +
drivers/dax/dax-private.h | 1 +
drivers/dax/bus.c | 3 +
drivers/dax/cxl.c | 1 +
drivers/dax/hmem/hmem.c | 1 +
drivers/dax/kmem.c | 8 +-
drivers/dax/pmem.c | 1 +
mm/memory_hotplug.c | 214 ++++++++++++++++++++++++++++++++--------------
8 files changed, 163 insertions(+), 67 deletions(-)
---
base-commit: 25b5b1a0646c3d39e1d885e27c10be1c9e202bf2
change-id: 20230613-vv-kmem_memmap-5483c8d04279
Best regards,
--
Vishal Verma <[email protected]>
A review of the memmap_on_memory modifications to add_memory_resource()
revealed an instance of an open-coded kmemdup(). Replace it with
kmemdup().
Cc: Andrew Morton <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Dan Williams <[email protected]>
Reported-by: Dan Williams <[email protected]>
Signed-off-by: Vishal Verma <[email protected]>
---
mm/memory_hotplug.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index f8d3e7427e32..6be7de9efa55 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1439,11 +1439,11 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
if (mhp_flags & MHP_MEMMAP_ON_MEMORY) {
if (mhp_supports_memmap_on_memory(size)) {
mhp_altmap.free = memory_block_memmap_on_memory_pages();
- params.altmap = kmalloc(sizeof(struct vmem_altmap), GFP_KERNEL);
+ params.altmap = kmemdup(&mhp_altmap,
+ sizeof(struct vmem_altmap),
+ GFP_KERNEL);
if (!params.altmap)
goto error;
-
- memcpy(params.altmap, &mhp_altmap, sizeof(mhp_altmap));
}
/* fallback to not using altmap */
}
--
2.41.0
The MHP_MEMMAP_ON_MEMORY flag for hotplugged memory is restricted to
'memblock_size' chunks of memory being added. Adding a larger span of
memory precludes memmap_on_memory semantics.
For users of hotplug such as kmem, large amounts of memory might get
added from the CXL subsystem. In some cases, this amount may exceed the
available 'main memory' to store the memmap for the memory being added.
In this case, it is useful to have a way to place the memmap on the
memory being added, even if it means splitting the addition into
memblock-sized chunks.
Change add_memory_resource() to loop over memblock-sized chunks of
memory if caller requested memmap_on_memory, and if other conditions for
it are met. Teach try_remove_memory() to also expect that a memory
range being removed might have been split up into memblock sized chunks,
and to loop through those as needed.
This does preclude being able to use PUD mappings in the direct map; a
proposal to how this could be optimized in the future is laid out
here[1].
[1]: https://lore.kernel.org/linux-mm/[email protected]/
Cc: Andrew Morton <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Dan Williams <[email protected]>
Cc: Dave Jiang <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Huang Ying <[email protected]>
Suggested-by: David Hildenbrand <[email protected]>
Reviewed-by: Dan Williams <[email protected]>
Signed-off-by: Vishal Verma <[email protected]>
---
mm/memory_hotplug.c | 214 ++++++++++++++++++++++++++++++++++++----------------
1 file changed, 148 insertions(+), 66 deletions(-)
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 6be7de9efa55..83e5ec377aad 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1380,6 +1380,43 @@ static bool mhp_supports_memmap_on_memory(unsigned long size)
return arch_supports_memmap_on_memory(vmemmap_size);
}
+static int add_memory_create_devices(int nid, struct memory_group *group,
+ u64 start, u64 size, mhp_t mhp_flags)
+{
+ struct mhp_params params = { .pgprot = pgprot_mhp(PAGE_KERNEL) };
+ struct vmem_altmap mhp_altmap = {
+ .base_pfn = PHYS_PFN(start),
+ .end_pfn = PHYS_PFN(start + size - 1),
+ };
+ int ret;
+
+ if ((mhp_flags & MHP_MEMMAP_ON_MEMORY)) {
+ mhp_altmap.free = memory_block_memmap_on_memory_pages();
+ params.altmap = kmemdup(&mhp_altmap, sizeof(struct vmem_altmap),
+ GFP_KERNEL);
+ if (!params.altmap)
+ return -ENOMEM;
+ }
+
+ /* call arch's memory hotadd */
+ ret = arch_add_memory(nid, start, size, ¶ms);
+ if (ret < 0)
+ goto error;
+
+ /* create memory block devices after memory was added */
+ ret = create_memory_block_devices(start, size, params.altmap, group);
+ if (ret)
+ goto err_bdev;
+
+ return 0;
+
+err_bdev:
+ arch_remove_memory(start, size, NULL);
+error:
+ kfree(params.altmap);
+ return ret;
+}
+
/*
* NOTE: The caller must call lock_device_hotplug() to serialize hotplug
* and online/offline operations (triggered e.g. by sysfs).
@@ -1388,14 +1425,10 @@ static bool mhp_supports_memmap_on_memory(unsigned long size)
*/
int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
{
- struct mhp_params params = { .pgprot = pgprot_mhp(PAGE_KERNEL) };
+ unsigned long memblock_size = memory_block_size_bytes();
enum memblock_flags memblock_flags = MEMBLOCK_NONE;
- struct vmem_altmap mhp_altmap = {
- .base_pfn = PHYS_PFN(res->start),
- .end_pfn = PHYS_PFN(res->end),
- };
struct memory_group *group = NULL;
- u64 start, size;
+ u64 start, size, cur_start;
bool new_node = false;
int ret;
@@ -1436,28 +1469,21 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
/*
* Self hosted memmap array
*/
- if (mhp_flags & MHP_MEMMAP_ON_MEMORY) {
- if (mhp_supports_memmap_on_memory(size)) {
- mhp_altmap.free = memory_block_memmap_on_memory_pages();
- params.altmap = kmemdup(&mhp_altmap,
- sizeof(struct vmem_altmap),
- GFP_KERNEL);
- if (!params.altmap)
+ if ((mhp_flags & MHP_MEMMAP_ON_MEMORY) &&
+ mhp_supports_memmap_on_memory(memblock_size)) {
+ for (cur_start = start; cur_start < start + size;
+ cur_start += memblock_size) {
+ ret = add_memory_create_devices(nid, group, cur_start,
+ memblock_size,
+ mhp_flags);
+ if (ret)
goto error;
}
- /* fallback to not using altmap */
- }
-
- /* call arch's memory hotadd */
- ret = arch_add_memory(nid, start, size, ¶ms);
- if (ret < 0)
- goto error_free;
-
- /* create memory block devices after memory was added */
- ret = create_memory_block_devices(start, size, params.altmap, group);
- if (ret) {
- arch_remove_memory(start, size, NULL);
- goto error_free;
+ } else {
+ ret = add_memory_create_devices(nid, group, start, size,
+ mhp_flags);
+ if (ret)
+ goto error;
}
if (new_node) {
@@ -1494,8 +1520,6 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
walk_memory_blocks(start, size, NULL, online_memory_block);
return ret;
-error_free:
- kfree(params.altmap);
error:
if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK))
memblock_remove(start, size);
@@ -2076,6 +2100,23 @@ static int test_has_altmap_cb(struct memory_block *mem, void *arg)
return 0;
}
+struct memory_range_altmap_info {
+ u64 num_memblocks;
+ u64 num_altmaps;
+};
+
+static int count_memory_range_altmaps_cb(struct memory_block *mem, void *arg)
+{
+ struct memory_range_altmap_info *altmap_info =
+ (struct memory_range_altmap_info *)arg;
+
+ altmap_info->num_memblocks += 1;
+ if (mem->altmap)
+ altmap_info->num_altmaps += 1;
+
+ return 0;
+}
+
static int check_cpu_on_node(int nid)
{
int cpu;
@@ -2146,11 +2187,75 @@ void try_offline_node(int nid)
}
EXPORT_SYMBOL(try_offline_node);
-static int __ref try_remove_memory(u64 start, u64 size)
+static void __ref remove_memory_blocks_and_altmaps(u64 start, u64 size)
{
- struct memory_block *mem;
- int rc = 0, nid = NUMA_NO_NODE;
+ unsigned long memblock_size = memory_block_size_bytes();
struct vmem_altmap *altmap = NULL;
+ struct memory_block *mem;
+ u64 cur_start;
+ int rc;
+
+ /*
+ * For memmap_on_memory, the altmaps could have been added on
+ * a per-memblock basis. Loop through the entire range if so,
+ * and remove each memblock and its altmap.
+ */
+ for (cur_start = start; cur_start < start + size;
+ cur_start += memblock_size) {
+ rc = walk_memory_blocks(cur_start, memblock_size, &mem,
+ test_has_altmap_cb);
+ if (rc) {
+ altmap = mem->altmap;
+ /*
+ * Mark altmap NULL so that we can add a debug
+ * check on memblock free.
+ */
+ mem->altmap = NULL;
+ }
+
+ /*
+ * Memory block device removal under the device_hotplug_lock is
+ * a barrier against racing online attempts.
+ */
+ remove_memory_block_devices(cur_start, memblock_size);
+
+ arch_remove_memory(cur_start, memblock_size, altmap);
+
+ /* Verify that all vmemmap pages have actually been freed. */
+ if (altmap) {
+ WARN(altmap->alloc, "Altmap not fully unmapped");
+ kfree(altmap);
+ }
+ }
+}
+
+static int memblocks_have_altmaps(u64 start, u64 size)
+{
+ struct memory_range_altmap_info altmap_info = {
+ .num_memblocks = 0,
+ .num_altmaps = 0
+ };
+
+ if (!mhp_memmap_on_memory())
+ return 0;
+
+ walk_memory_blocks(start, size, &altmap_info,
+ count_memory_range_altmaps_cb);
+
+ if (!altmap_info.num_altmaps)
+ return 0;
+
+ if (altmap_info.num_memblocks != altmap_info.num_altmaps) {
+ WARN_ONCE(1, "Not all memblocks in range have altmaps");
+ return -EINVAL;
+ }
+
+ return 1;
+}
+
+static int __ref try_remove_memory(u64 start, u64 size)
+{
+ int rc, nid = NUMA_NO_NODE;
BUG_ON(check_hotplug_memory_range(start, size));
@@ -2167,45 +2272,21 @@ static int __ref try_remove_memory(u64 start, u64 size)
if (rc)
return rc;
- /*
- * We only support removing memory added with MHP_MEMMAP_ON_MEMORY in
- * the same granularity it was added - a single memory block.
- */
- if (mhp_memmap_on_memory()) {
- rc = walk_memory_blocks(start, size, &mem, test_has_altmap_cb);
- if (rc) {
- if (size != memory_block_size_bytes()) {
- pr_warn("Refuse to remove %#llx - %#llx,"
- "wrong granularity\n",
- start, start + size);
- return -EINVAL;
- }
- altmap = mem->altmap;
- /*
- * Mark altmap NULL so that we can add a debug
- * check on memblock free.
- */
- mem->altmap = NULL;
- }
- }
-
/* remove memmap entry */
firmware_map_remove(start, start + size, "System RAM");
- /*
- * Memory block device removal under the device_hotplug_lock is
- * a barrier against racing online attempts.
- */
- remove_memory_block_devices(start, size);
-
mem_hotplug_begin();
- arch_remove_memory(start, size, altmap);
-
- /* Verify that all vmemmap pages have actually been freed. */
- if (altmap) {
- WARN(altmap->alloc, "Altmap not fully unmapped");
- kfree(altmap);
+ rc = memblocks_have_altmaps(start, size);
+ if (rc < 0) {
+ goto err;
+ } else if (rc == 0) {
+ /* no altmaps, do the removal directly */
+ remove_memory_block_devices(start, size);
+ arch_remove_memory(start, size, NULL);
+ } else {
+ /* all memblocks in the range have altmaps */
+ remove_memory_blocks_and_altmaps(start, size);
}
if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) {
@@ -2218,8 +2299,9 @@ static int __ref try_remove_memory(u64 start, u64 size)
if (nid != NUMA_NO_NODE)
try_offline_node(nid);
+err:
mem_hotplug_done();
- return 0;
+ return (rc < 0 ? rc : 0);
}
/**
--
2.41.0
Vishal Verma <[email protected]> writes:
> The MHP_MEMMAP_ON_MEMORY flag for hotplugged memory is restricted to
> 'memblock_size' chunks of memory being added. Adding a larger span of
> memory precludes memmap_on_memory semantics.
>
> For users of hotplug such as kmem, large amounts of memory might get
> added from the CXL subsystem. In some cases, this amount may exceed the
> available 'main memory' to store the memmap for the memory being added.
> In this case, it is useful to have a way to place the memmap on the
> memory being added, even if it means splitting the addition into
> memblock-sized chunks.
>
> Change add_memory_resource() to loop over memblock-sized chunks of
> memory if caller requested memmap_on_memory, and if other conditions for
> it are met. Teach try_remove_memory() to also expect that a memory
> range being removed might have been split up into memblock sized chunks,
> and to loop through those as needed.
>
> This does preclude being able to use PUD mappings in the direct map; a
> proposal to how this could be optimized in the future is laid out
> here[1].
>
> [1]: https://lore.kernel.org/linux-mm/[email protected]/
>
> Cc: Andrew Morton <[email protected]>
> Cc: David Hildenbrand <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Oscar Salvador <[email protected]>
> Cc: Dan Williams <[email protected]>
> Cc: Dave Jiang <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Huang Ying <[email protected]>
> Suggested-by: David Hildenbrand <[email protected]>
> Reviewed-by: Dan Williams <[email protected]>
> Signed-off-by: Vishal Verma <[email protected]>
> ---
> mm/memory_hotplug.c | 214 ++++++++++++++++++++++++++++++++++++----------------
> 1 file changed, 148 insertions(+), 66 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 6be7de9efa55..83e5ec377aad 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1380,6 +1380,43 @@ static bool mhp_supports_memmap_on_memory(unsigned long size)
> return arch_supports_memmap_on_memory(vmemmap_size);
> }
>
> +static int add_memory_create_devices(int nid, struct memory_group *group,
> + u64 start, u64 size, mhp_t mhp_flags)
> +{
> + struct mhp_params params = { .pgprot = pgprot_mhp(PAGE_KERNEL) };
> + struct vmem_altmap mhp_altmap = {
> + .base_pfn = PHYS_PFN(start),
> + .end_pfn = PHYS_PFN(start + size - 1),
> + };
> + int ret;
> +
> + if ((mhp_flags & MHP_MEMMAP_ON_MEMORY)) {
> + mhp_altmap.free = memory_block_memmap_on_memory_pages();
> + params.altmap = kmemdup(&mhp_altmap, sizeof(struct vmem_altmap),
> + GFP_KERNEL);
> + if (!params.altmap)
> + return -ENOMEM;
> + }
> +
> + /* call arch's memory hotadd */
> + ret = arch_add_memory(nid, start, size, ¶ms);
> + if (ret < 0)
> + goto error;
> +
> + /* create memory block devices after memory was added */
> + ret = create_memory_block_devices(start, size, params.altmap, group);
> + if (ret)
> + goto err_bdev;
> +
> + return 0;
> +
> +err_bdev:
> + arch_remove_memory(start, size, NULL);
> +error:
> + kfree(params.altmap);
> + return ret;
> +}
> +
> /*
> * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
> * and online/offline operations (triggered e.g. by sysfs).
> @@ -1388,14 +1425,10 @@ static bool mhp_supports_memmap_on_memory(unsigned long size)
> */
> int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
> {
> - struct mhp_params params = { .pgprot = pgprot_mhp(PAGE_KERNEL) };
> + unsigned long memblock_size = memory_block_size_bytes();
> enum memblock_flags memblock_flags = MEMBLOCK_NONE;
> - struct vmem_altmap mhp_altmap = {
> - .base_pfn = PHYS_PFN(res->start),
> - .end_pfn = PHYS_PFN(res->end),
> - };
> struct memory_group *group = NULL;
> - u64 start, size;
> + u64 start, size, cur_start;
> bool new_node = false;
> int ret;
>
> @@ -1436,28 +1469,21 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
> /*
> * Self hosted memmap array
> */
> - if (mhp_flags & MHP_MEMMAP_ON_MEMORY) {
> - if (mhp_supports_memmap_on_memory(size)) {
> - mhp_altmap.free = memory_block_memmap_on_memory_pages();
> - params.altmap = kmemdup(&mhp_altmap,
> - sizeof(struct vmem_altmap),
> - GFP_KERNEL);
> - if (!params.altmap)
> + if ((mhp_flags & MHP_MEMMAP_ON_MEMORY) &&
> + mhp_supports_memmap_on_memory(memblock_size)) {
> + for (cur_start = start; cur_start < start + size;
> + cur_start += memblock_size) {
> + ret = add_memory_create_devices(nid, group, cur_start,
> + memblock_size,
> + mhp_flags);
> + if (ret)
> goto error;
> }
> - /* fallback to not using altmap */
> - }
> -
> - /* call arch's memory hotadd */
> - ret = arch_add_memory(nid, start, size, ¶ms);
> - if (ret < 0)
> - goto error_free;
> -
> - /* create memory block devices after memory was added */
> - ret = create_memory_block_devices(start, size, params.altmap, group);
> - if (ret) {
> - arch_remove_memory(start, size, NULL);
> - goto error_free;
> + } else {
> + ret = add_memory_create_devices(nid, group, start, size,
> + mhp_flags);
IIUC, if (mhp_flags & MHP_MEMMAP_ON_MEMORY) == true and
mhp_supports_memmap_on_memory(memblock_size) == false, we will go here
and allocate params.altmap in add_memory_create_devices(). If so, it
seems better to pass whether to create altmap instead of mhp_flags to
add_memory_create_devices().
--
Best Regards,
Huang, Ying
> + if (ret)
> + goto error;
> }
>
> if (new_node) {
[snip]
On 17.10.23 07:44, Vishal Verma wrote:
> A review of the memmap_on_memory modifications to add_memory_resource()
> revealed an instance of an open-coded kmemdup(). Replace it with
> kmemdup().
>
> Cc: Andrew Morton <[email protected]>
> Cc: David Hildenbrand <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Oscar Salvador <[email protected]>
> Cc: Dan Williams <[email protected]>
> Reported-by: Dan Williams <[email protected]>
> Signed-off-by: Vishal Verma <[email protected]>
> ---
> mm/memory_hotplug.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index f8d3e7427e32..6be7de9efa55 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1439,11 +1439,11 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
> if (mhp_flags & MHP_MEMMAP_ON_MEMORY) {
> if (mhp_supports_memmap_on_memory(size)) {
> mhp_altmap.free = memory_block_memmap_on_memory_pages();
> - params.altmap = kmalloc(sizeof(struct vmem_altmap), GFP_KERNEL);
> + params.altmap = kmemdup(&mhp_altmap,
> + sizeof(struct vmem_altmap),
> + GFP_KERNEL);
> if (!params.altmap)
> goto error;
> -
> - memcpy(params.altmap, &mhp_altmap, sizeof(mhp_altmap));
> }
> /* fallback to not using altmap */
> }
>
Reviewed-by: David Hildenbrand <[email protected]>
--
Cheers,
David / dhildenb
On 17.10.23 07:44, Vishal Verma wrote:
> The MHP_MEMMAP_ON_MEMORY flag for hotplugged memory is restricted to
> 'memblock_size' chunks of memory being added. Adding a larger span of
> memory precludes memmap_on_memory semantics.
>
> For users of hotplug such as kmem, large amounts of memory might get
> added from the CXL subsystem. In some cases, this amount may exceed the
> available 'main memory' to store the memmap for the memory being added.
> In this case, it is useful to have a way to place the memmap on the
> memory being added, even if it means splitting the addition into
> memblock-sized chunks.
>
> Change add_memory_resource() to loop over memblock-sized chunks of
> memory if caller requested memmap_on_memory, and if other conditions for
> it are met. Teach try_remove_memory() to also expect that a memory
> range being removed might have been split up into memblock sized chunks,
> and to loop through those as needed.
>
> This does preclude being able to use PUD mappings in the direct map; a
> proposal to how this could be optimized in the future is laid out
> here[1].
>
> [1]: https://lore.kernel.org/linux-mm/[email protected]/
>
> Cc: Andrew Morton <[email protected]>
> Cc: David Hildenbrand <[email protected]>
> Cc: Michal Hocko <[email protected]>
> Cc: Oscar Salvador <[email protected]>
> Cc: Dan Williams <[email protected]>
> Cc: Dave Jiang <[email protected]>
> Cc: Dave Hansen <[email protected]>
> Cc: Huang Ying <[email protected]>
> Suggested-by: David Hildenbrand <[email protected]>
> Reviewed-by: Dan Williams <[email protected]>
> Signed-off-by: Vishal Verma <[email protected]>
> ---
> mm/memory_hotplug.c | 214 ++++++++++++++++++++++++++++++++++++----------------
> 1 file changed, 148 insertions(+), 66 deletions(-)
>
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 6be7de9efa55..83e5ec377aad 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1380,6 +1380,43 @@ static bool mhp_supports_memmap_on_memory(unsigned long size)
> return arch_supports_memmap_on_memory(vmemmap_size);
> }
>
> +static int add_memory_create_devices(int nid, struct memory_group *group,
> + u64 start, u64 size, mhp_t mhp_flags)
> +{
> + struct mhp_params params = { .pgprot = pgprot_mhp(PAGE_KERNEL) };
> + struct vmem_altmap mhp_altmap = {
> + .base_pfn = PHYS_PFN(start),
> + .end_pfn = PHYS_PFN(start + size - 1),
> + };
> + int ret;
> +
> + if ((mhp_flags & MHP_MEMMAP_ON_MEMORY)) {
> + mhp_altmap.free = memory_block_memmap_on_memory_pages();
> + params.altmap = kmemdup(&mhp_altmap, sizeof(struct vmem_altmap),
> + GFP_KERNEL);
> + if (!params.altmap)
> + return -ENOMEM;
> + }
> +
> + /* call arch's memory hotadd */
> + ret = arch_add_memory(nid, start, size, ¶ms);
> + if (ret < 0)
> + goto error;
> +
> + /* create memory block devices after memory was added */
> + ret = create_memory_block_devices(start, size, params.altmap, group);
> + if (ret)
> + goto err_bdev;
> +
> + return 0;
> +
> +err_bdev:
> + arch_remove_memory(start, size, NULL);
> +error:
> + kfree(params.altmap);
> + return ret;
> +}
> +
> /*
> * NOTE: The caller must call lock_device_hotplug() to serialize hotplug
> * and online/offline operations (triggered e.g. by sysfs).
> @@ -1388,14 +1425,10 @@ static bool mhp_supports_memmap_on_memory(unsigned long size)
> */
> int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
> {
> - struct mhp_params params = { .pgprot = pgprot_mhp(PAGE_KERNEL) };
> + unsigned long memblock_size = memory_block_size_bytes();
> enum memblock_flags memblock_flags = MEMBLOCK_NONE;
> - struct vmem_altmap mhp_altmap = {
> - .base_pfn = PHYS_PFN(res->start),
> - .end_pfn = PHYS_PFN(res->end),
> - };
> struct memory_group *group = NULL;
> - u64 start, size;
> + u64 start, size, cur_start;
> bool new_node = false;
> int ret;
>
> @@ -1436,28 +1469,21 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
> /*
> * Self hosted memmap array
> */
> - if (mhp_flags & MHP_MEMMAP_ON_MEMORY) {
> - if (mhp_supports_memmap_on_memory(size)) {
> - mhp_altmap.free = memory_block_memmap_on_memory_pages();
> - params.altmap = kmemdup(&mhp_altmap,
> - sizeof(struct vmem_altmap),
> - GFP_KERNEL);
> - if (!params.altmap)
> + if ((mhp_flags & MHP_MEMMAP_ON_MEMORY) &&
> + mhp_supports_memmap_on_memory(memblock_size)) {
> + for (cur_start = start; cur_start < start + size;
> + cur_start += memblock_size) {
> + ret = add_memory_create_devices(nid, group, cur_start,
> + memblock_size,
> + mhp_flags);
Just like on the removal part, that function doesn't make any sense to
be called with altmap and a bigger range.
Maybe better also move that loop into a function called
"create_altmap_and_memory_blocks()" , to be the opposite of
"remove_memory_blocks_and_altmaps()".
Then you can keep the existing !altmap code here in the "else" case.
Again, similar to the removal code below.
> + if (ret)
> goto error;
> }
> - /* fallback to not using altmap */
> - }
> -
> - /* call arch's memory hotadd */
> - ret = arch_add_memory(nid, start, size, ¶ms);
> - if (ret < 0)
> - goto error_free;
> -
> - /* create memory block devices after memory was added */
> - ret = create_memory_block_devices(start, size, params.altmap, group);
> - if (ret) {
> - arch_remove_memory(start, size, NULL);
> - goto error_free;
> + } else {
> + ret = add_memory_create_devices(nid, group, start, size,
> + mhp_flags);
> + if (ret)
> + goto error;
> }
>
> if (new_node) {
> @@ -1494,8 +1520,6 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
> walk_memory_blocks(start, size, NULL, online_memory_block);
>
> return ret;
> -error_free:
> - kfree(params.altmap);
> error:
> if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK))
> memblock_remove(start, size);
> @@ -2076,6 +2100,23 @@ static int test_has_altmap_cb(struct memory_block *mem, void *arg)
> return 0;
> }
[...]
> +
> +static int memblocks_have_altmaps(u64 start, u64 size)
> +{
> + struct memory_range_altmap_info altmap_info = {
> + .num_memblocks = 0,
> + .num_altmaps = 0
> + };
You can get the number of memblocks simply by "size /
memory_block_size_bytes()". So you can avoid the "struct" and just pass
an int.
> +
> + if (!mhp_memmap_on_memory())
> + return 0;
> +
> + walk_memory_blocks(start, size, &altmap_info,
> + count_memory_range_altmaps_cb);
> +
> + if (!altmap_info.num_altmaps)
> + return 0;
> +
> + if (altmap_info.num_memblocks != altmap_info.num_altmaps) {
> + WARN_ONCE(1, "Not all memblocks in range have altmaps");
> + return -EINVAL;
> + }
> +
> + return 1;
> +}
> +
> +static int __ref try_remove_memory(u64 start, u64 size)
> +{
> + int rc, nid = NUMA_NO_NODE;
>
> BUG_ON(check_hotplug_memory_range(start, size));
>
> @@ -2167,45 +2272,21 @@ static int __ref try_remove_memory(u64 start, u64 size)
> if (rc)
> return rc;
>
> - /*
> - * We only support removing memory added with MHP_MEMMAP_ON_MEMORY in
> - * the same granularity it was added - a single memory block.
> - */
> - if (mhp_memmap_on_memory()) {
> - rc = walk_memory_blocks(start, size, &mem, test_has_altmap_cb);
> - if (rc) {
> - if (size != memory_block_size_bytes()) {
> - pr_warn("Refuse to remove %#llx - %#llx,"
> - "wrong granularity\n",
> - start, start + size);
> - return -EINVAL;
> - }
> - altmap = mem->altmap;
> - /*
> - * Mark altmap NULL so that we can add a debug
> - * check on memblock free.
> - */
> - mem->altmap = NULL;
> - }
> - }
> -
> /* remove memmap entry */
> firmware_map_remove(start, start + size, "System RAM");
>
> - /*
> - * Memory block device removal under the device_hotplug_lock is
> - * a barrier against racing online attempts.
> - */
Maybe move that comment into the else branch and not into
remove_memory_blocks_and_altmaps
> - remove_memory_block_devices(start, size);
> -
> mem_hotplug_begin();
>
> - arch_remove_memory(start, size, altmap);
> -
> - /* Verify that all vmemmap pages have actually been freed. */
> - if (altmap) {
> - WARN(altmap->alloc, "Altmap not fully unmapped");
> - kfree(altmap);
> + rc = memblocks_have_altmaps(start, size);
Don't use the term memblocks here, to not confuse it with the memblock
allocator.
"memory blocks" or "memory block devices". it's complicated.
> + if (rc < 0) {
> + goto err;
> + } else if (rc == 0) {
> + /* no altmaps, do the removal directly */
> + remove_memory_block_devices(start, size);
> + arch_remove_memory(start, size, NULL);
> + } else {
> + /* all memblocks in the range have altmaps */
> + remove_memory_blocks_and_altmaps(start, size);
> }
>
> if (IS_ENABLED(CONFIG_ARCH_KEEP_MEMBLOCK)) {
> @@ -2218,8 +2299,9 @@ static int __ref try_remove_memory(u64 start, u64 size)
> if (nid != NUMA_NO_NODE)
> try_offline_node(nid);
>
> +err:
> mem_hotplug_done();
> - return 0;
> + return (rc < 0 ? rc : 0);
> }
>
> /**
>
--
Cheers,
David / dhildenb