Re: [PATCH v3 4/7] mm/hotplug: Allow pageblock alignment via altmap reservation
On 12.07.23 15:50, Aneesh Kumar K.V wrote:
David Hildenbrand writes:
On 12.07.23 05:16, Aneesh Kumar K V wrote:
On 7/11/23 10:49 PM, David Hildenbrand wrote:
On 11.07.23 06:48, Aneesh Kumar K.V wrote:
Add a new kconfig option that can be selected if we want to allow
pageblock alignment by reserving pages in the vmemmap altmap area.
This implies we will be reserving some pages for every memoryblock
This also allows the memmap on memory feature to be widely useful
with different memory block size values.
"reserving pages" is a nice way of saying "wasting memory". :) Let's spell that
out.
I think we have to find a better name for this, and I think we should have a
toggle similar to memory_hotplug.memmap_on_memory. This should be an admin
decision, not some kernel config option.
memory_hotplug.force_memmap_on_memory
"Enable the memmap on memory feature even if it could result in memory waste
due to memmap size limitations. For example, if the memmap for a memory block
requires 1 MiB, but the pageblock size is 2 MiB, 1 MiB
of hotplugged memory will be wasted. Note that there are still cases where the
feature cannot be enforced: for example, if the memmap is smaller than a single
page, or if the architecture does not support the forced mode in all
configurations."
Thoughts?
With module parameter, do we still need the Kconfig option?
No.
Sleeping over this, maybe we can convert the existing
memory_hotplug.memmap_on_memory parameter to also accept "force".
How about this?
modified mm/memory_hotplug.c
@@ -45,13 +45,67 @@
/*
* memory_hotplug.memmap_on_memory parameter
*/
-static bool memmap_on_memory __ro_after_init;
-module_param(memmap_on_memory, bool, 0444);
-MODULE_PARM_DESC(memmap_on_memory, "Enable memmap on memory for memory
hotplug");
+enum {
+ MEMMAP_ON_MEMORY_DISABLE = 0,
+ MEMMAP_ON_MEMORY_ENABLE,
+ FORCE_MEMMAP_ON_MEMORY,
MEMMAP_ON_MEMORY_FORCE ?
+};
+static int memmap_mode __read_mostly = MEMMAP_ON_MEMORY_DISABLE;
+static const char *memmap_on_memory_to_str[] = {
+ [MEMMAP_ON_MEMORY_DISABLE] = "disable",
+ [MEMMAP_ON_MEMORY_ENABLE] = "enable",
+ [FORCE_MEMMAP_ON_MEMORY]= "force",
+};
+
+static inline unsigned long memory_block_align_base(unsigned long size)
+{
+ if (memmap_mode == FORCE_MEMMAP_ON_MEMORY) {
+ unsigned long align;
+ unsigned long nr_vmemmap_pages = size >> PAGE_SHIFT;
+ unsigned long vmemmap_size;
+
+ vmemmap_size = DIV_ROUND_UP(nr_vmemmap_pages * sizeof(struct
page), PAGE_SIZE);
+ align = pageblock_align(vmemmap_size) - vmemmap_size;
+ return align;
+ } else
+ return 0;
^ have to see that in action :)
+}
+
+static int set_memmap_mode(const char *val, const struct kernel_param *kp)
+{
+ int ret = sysfs_match_string(memmap_on_memory_to_str, val);
+
That would break existing cmdlines that eat Y/N/0/..., no?
Maybe try parsing "force/FORCE" first and then fallback to the common
bool parsing (kstrtobool).
Same when printing: handle "force" separately and then just print Y/N
like param_get_bool() used to do.
So you'd end up with Y/N/FORCE as output and Y/N/0/.../FORCE/force as input.
But I'm happy to hear about alternatives. Maybe a second parameter is
better ... but what name should it have "memmap_on_memory_force" sounds
wrong. We'd need a name that expresses that we might be wasting memory,
hm ...
+ if (ret < 0)
+ return ret;
+ *((int *)kp->arg) = ret;
+ if (ret == FORCE_MEMMAP_ON_MEMORY) {
+ pr_info("Memory hotplug will reserve %ld pages in each memory
block\n",
+ memory_block_align_base(memory_block_size_bytes()));
+ }
+ return 0;
+}
+
+static int get_memmap_mode(char *buffer, const struct kernel_param *kp)
+{
+ return sprintf(buffer, "%s\n", memmap_on_memory_to_str[*((int
*)kp->arg)]);
+}
+
+static const struct kernel_param_ops memmap_mode_ops = {
+ .set = set_memmap_mode,
+ .get = get_memmap_mode,
+};
+module_param_cb(memmap_on_memory, _mode_ops, _mode, 0644);
+MODULE_PARM_DESC(memmap_on_memory, "Enable memmap on memory for memory
hotplug\n"
+ "With value \"force\" it could result in memory waste due to memmap size
limitations \n"
+ "For example, if the memmap for a memory block requires 1 MiB, but the
pageblock \n"
+ "size is 2 MiB, 1 MiB of hotplugged memory will be wasted. Note that there
are \n"
+ "still cases where the feature cannot be enforced: for example, if the
memmap is \n"
+ "smaller than a single page, or if the architecture does not support the
forced \n"
+ "mode in all configurations. (disable/enable/force)");
static inline bool mhp_memmap_on_memory(void)
{
- return memmap_on_memory;
+ return !!memmap_mode;
}
#else
We can also enable runtime enable/disable/force the feature. We just
Re: [PATCH v3 4/7] mm/hotplug: Allow pageblock alignment via altmap reservation
David Hildenbrand writes:
> On 12.07.23 05:16, Aneesh Kumar K V wrote:
>> On 7/11/23 10:49 PM, David Hildenbrand wrote:
>>> On 11.07.23 06:48, Aneesh Kumar K.V wrote:
Add a new kconfig option that can be selected if we want to allow
pageblock alignment by reserving pages in the vmemmap altmap area.
This implies we will be reserving some pages for every memoryblock
This also allows the memmap on memory feature to be widely useful
with different memory block size values.
>>>
>>> "reserving pages" is a nice way of saying "wasting memory". :) Let's spell
>>> that out.
>>>
>>> I think we have to find a better name for this, and I think we should have
>>> a toggle similar to memory_hotplug.memmap_on_memory. This should be an
>>> admin decision, not some kernel config option.
>>>
>>>
>>> memory_hotplug.force_memmap_on_memory
>>>
>>> "Enable the memmap on memory feature even if it could result in memory
>>> waste due to memmap size limitations. For example, if the memmap for a
>>> memory block requires 1 MiB, but the pageblock size is 2 MiB, 1 MiB
>>> of hotplugged memory will be wasted. Note that there are still cases where
>>> the feature cannot be enforced: for example, if the memmap is smaller than
>>> a single page, or if the architecture does not support the forced mode in
>>> all configurations."
>>>
>>> Thoughts?
>>>
>>
>> With module parameter, do we still need the Kconfig option?
>
> No.
>
> Sleeping over this, maybe we can convert the existing
> memory_hotplug.memmap_on_memory parameter to also accept "force".
>
How about this?
modified mm/memory_hotplug.c
@@ -45,13 +45,67 @@
/*
* memory_hotplug.memmap_on_memory parameter
*/
-static bool memmap_on_memory __ro_after_init;
-module_param(memmap_on_memory, bool, 0444);
-MODULE_PARM_DESC(memmap_on_memory, "Enable memmap on memory for memory
hotplug");
+enum {
+ MEMMAP_ON_MEMORY_DISABLE = 0,
+ MEMMAP_ON_MEMORY_ENABLE,
+ FORCE_MEMMAP_ON_MEMORY,
+};
+static int memmap_mode __read_mostly = MEMMAP_ON_MEMORY_DISABLE;
+static const char *memmap_on_memory_to_str[] = {
+ [MEMMAP_ON_MEMORY_DISABLE] = "disable",
+ [MEMMAP_ON_MEMORY_ENABLE] = "enable",
+ [FORCE_MEMMAP_ON_MEMORY]= "force",
+};
+
+static inline unsigned long memory_block_align_base(unsigned long size)
+{
+ if (memmap_mode == FORCE_MEMMAP_ON_MEMORY) {
+ unsigned long align;
+ unsigned long nr_vmemmap_pages = size >> PAGE_SHIFT;
+ unsigned long vmemmap_size;
+
+ vmemmap_size = DIV_ROUND_UP(nr_vmemmap_pages * sizeof(struct
page), PAGE_SIZE);
+ align = pageblock_align(vmemmap_size) - vmemmap_size;
+ return align;
+ } else
+ return 0;
+}
+
+static int set_memmap_mode(const char *val, const struct kernel_param *kp)
+{
+ int ret = sysfs_match_string(memmap_on_memory_to_str, val);
+
+ if (ret < 0)
+ return ret;
+ *((int *)kp->arg) = ret;
+ if (ret == FORCE_MEMMAP_ON_MEMORY) {
+ pr_info("Memory hotplug will reserve %ld pages in each memory
block\n",
+ memory_block_align_base(memory_block_size_bytes()));
+ }
+ return 0;
+}
+
+static int get_memmap_mode(char *buffer, const struct kernel_param *kp)
+{
+ return sprintf(buffer, "%s\n", memmap_on_memory_to_str[*((int
*)kp->arg)]);
+}
+
+static const struct kernel_param_ops memmap_mode_ops = {
+ .set = set_memmap_mode,
+ .get = get_memmap_mode,
+};
+module_param_cb(memmap_on_memory, _mode_ops, _mode, 0644);
+MODULE_PARM_DESC(memmap_on_memory, "Enable memmap on memory for memory
hotplug\n"
+ "With value \"force\" it could result in memory waste due to memmap
size limitations \n"
+ "For example, if the memmap for a memory block requires 1 MiB, but the
pageblock \n"
+ "size is 2 MiB, 1 MiB of hotplugged memory will be wasted. Note that
there are \n"
+ "still cases where the feature cannot be enforced: for example, if the
memmap is \n"
+ "smaller than a single page, or if the architecture does not support
the forced \n"
+ "mode in all configurations. (disable/enable/force)");
static inline bool mhp_memmap_on_memory(void)
{
- return memmap_on_memory;
+ return !!memmap_mode;
}
#else
We can also enable runtime enable/disable/force the feature. We just
need to make sure on try_remove_memory we lookup for altmap correctly.
Re: [PATCH v3 4/7] mm/hotplug: Allow pageblock alignment via altmap reservation
On 12.07.23 05:16, Aneesh Kumar K V wrote: On 7/11/23 10:49 PM, David Hildenbrand wrote: On 11.07.23 06:48, Aneesh Kumar K.V wrote: Add a new kconfig option that can be selected if we want to allow pageblock alignment by reserving pages in the vmemmap altmap area. This implies we will be reserving some pages for every memoryblock This also allows the memmap on memory feature to be widely useful with different memory block size values. "reserving pages" is a nice way of saying "wasting memory". :) Let's spell that out. I think we have to find a better name for this, and I think we should have a toggle similar to memory_hotplug.memmap_on_memory. This should be an admin decision, not some kernel config option. memory_hotplug.force_memmap_on_memory "Enable the memmap on memory feature even if it could result in memory waste due to memmap size limitations. For example, if the memmap for a memory block requires 1 MiB, but the pageblock size is 2 MiB, 1 MiB of hotplugged memory will be wasted. Note that there are still cases where the feature cannot be enforced: for example, if the memmap is smaller than a single page, or if the architecture does not support the forced mode in all configurations." Thoughts? With module parameter, do we still need the Kconfig option? No. Sleeping over this, maybe we can convert the existing memory_hotplug.memmap_on_memory parameter to also accept "force". -- Cheers, David / dhildenb
Re: [PATCH v3 4/7] mm/hotplug: Allow pageblock alignment via altmap reservation
On 7/11/23 10:49 PM, David Hildenbrand wrote: > On 11.07.23 06:48, Aneesh Kumar K.V wrote: >> Add a new kconfig option that can be selected if we want to allow >> pageblock alignment by reserving pages in the vmemmap altmap area. >> This implies we will be reserving some pages for every memoryblock >> This also allows the memmap on memory feature to be widely useful >> with different memory block size values. > > "reserving pages" is a nice way of saying "wasting memory". :) Let's spell > that out. > > I think we have to find a better name for this, and I think we should have a > toggle similar to memory_hotplug.memmap_on_memory. This should be an admin > decision, not some kernel config option. > > > memory_hotplug.force_memmap_on_memory > > "Enable the memmap on memory feature even if it could result in memory waste > due to memmap size limitations. For example, if the memmap for a memory block > requires 1 MiB, but the pageblock size is 2 MiB, 1 MiB > of hotplugged memory will be wasted. Note that there are still cases where > the feature cannot be enforced: for example, if the memmap is smaller than a > single page, or if the architecture does not support the forced mode in all > configurations." > > Thoughts? > With module parameter, do we still need the Kconfig option? -aneesh
Re: [PATCH v3 4/7] mm/hotplug: Allow pageblock alignment via altmap reservation
On 11.07.23 06:48, Aneesh Kumar K.V wrote:
Add a new kconfig option that can be selected if we want to allow
pageblock alignment by reserving pages in the vmemmap altmap area.
This implies we will be reserving some pages for every memoryblock
This also allows the memmap on memory feature to be widely useful
with different memory block size values.
"reserving pages" is a nice way of saying "wasting memory". :) Let's
spell that out.
I think we have to find a better name for this, and I think we should
have a toggle similar to memory_hotplug.memmap_on_memory. This should be
an admin decision, not some kernel config option.
memory_hotplug.force_memmap_on_memory
"Enable the memmap on memory feature even if it could result in memory
waste due to memmap size limitations. For example, if the memmap for a
memory block requires 1 MiB, but the pageblock size is 2 MiB, 1 MiB
of hotplugged memory will be wasted. Note that there are still cases
where the feature cannot be enforced: for example, if the memmap is
smaller than a single page, or if the architecture does not support the
forced mode in all configurations."
Thoughts?
Signed-off-by: Aneesh Kumar K.V
---
mm/Kconfig | 9 +++
mm/memory_hotplug.c | 59 +
2 files changed, 58 insertions(+), 10 deletions(-)
diff --git a/mm/Kconfig b/mm/Kconfig
index 932349271e28..88a1472b2086 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -570,6 +570,15 @@ config MHP_MEMMAP_ON_MEMORY
depends on MEMORY_HOTPLUG && SPARSEMEM_VMEMMAP
depends on ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
+config MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY
+ bool "Allow Reserving pages for page block aligment"
+ depends on MHP_MEMMAP_ON_MEMORY
+ help
+ This option allows memmap on memory feature to be more useful
+ with different memory block sizes. This is achieved by marking some
pages
+ in each memory block as reserved so that we can get page-block alignment
+ for the remaining pages.
+
endif # MEMORY_HOTPLUG
config ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 07c99b0cc371..f36aec1f7626 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1252,15 +1252,17 @@ static inline bool
arch_supports_memmap_on_memory(unsigned long size)
{
unsigned long nr_vmemmap_pages = size >> PAGE_SHIFT;
unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
- unsigned long remaining_size = size - vmemmap_size;
- return IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
- IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT));
+ return IS_ALIGNED(vmemmap_size, PMD_SIZE);
}
#endif
static bool mhp_supports_memmap_on_memory(unsigned long size)
{
+ unsigned long nr_vmemmap_pages = size >> PAGE_SHIFT;
+ unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
+ unsigned long remaining_size = size - vmemmap_size;
+
/*
* Besides having arch support and the feature enabled at runtime, we
* need a few more assumptions to hold true:
@@ -1287,9 +1289,30 @@ static bool mhp_supports_memmap_on_memory(unsigned long
size)
* altmap as an alternative source of memory, and we do not
exactly
* populate a single PMD.
*/
- return mhp_memmap_on_memory() &&
- size == memory_block_size_bytes() &&
- arch_supports_memmap_on_memory(size);
+ if (!mhp_memmap_on_memory() || size != memory_block_size_bytes())
+ return false;
+/*
+ * Without page reservation remaining pages should be pageblock
aligned.
+ */
+ if (!IS_ENABLED(CONFIG_MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY) &&
+ !IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT)))
+ return false;
+
+ return arch_supports_memmap_on_memory(size);
+}
+
+static inline unsigned long memory_block_align_base(unsigned long size)
+{
+ if (IS_ENABLED(CONFIG_MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY)) {
+ unsigned long align;
+ unsigned long nr_vmemmap_pages = size >> PAGE_SHIFT;
+ unsigned long vmemmap_size;
+
+ vmemmap_size = (nr_vmemmap_pages * sizeof(struct page)) >>
PAGE_SHIFT;
+ align = pageblock_align(vmemmap_size) - vmemmap_size;
We should probably have a helper to calculate
a) the unaligned vmemmap size, for example used in
arch_supports_memmap_on_memory()
b) the pageblock-aligned vmemmap size.
--
Cheers,
David / dhildenb
Re: [PATCH v3 4/7] mm/hotplug: Allow pageblock alignment via altmap reservation
On 7/11/23 11:51 AM, Huang, Ying wrote:
> "Aneesh Kumar K.V" writes:
>
>> Add a new kconfig option that can be selected if we want to allow
>> pageblock alignment by reserving pages in the vmemmap altmap area.
>> This implies we will be reserving some pages for every memoryblock
>> This also allows the memmap on memory feature to be widely useful
>> with different memory block size values.
>>
>> Signed-off-by: Aneesh Kumar K.V
>> ---
>> mm/Kconfig | 9 +++
>> mm/memory_hotplug.c | 59 +
>> 2 files changed, 58 insertions(+), 10 deletions(-)
>>
>> diff --git a/mm/Kconfig b/mm/Kconfig
>> index 932349271e28..88a1472b2086 100644
>> --- a/mm/Kconfig
>> +++ b/mm/Kconfig
>> @@ -570,6 +570,15 @@ config MHP_MEMMAP_ON_MEMORY
>> depends on MEMORY_HOTPLUG && SPARSEMEM_VMEMMAP
>> depends on ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
>>
>> +config MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY
>> + bool "Allow Reserving pages for page block aligment"
>> + depends on MHP_MEMMAP_ON_MEMORY
>> + help
>> +This option allows memmap on memory feature to be more useful
>> +with different memory block sizes. This is achieved by marking some
>> pages
>> +in each memory block as reserved so that we can get page-block alignment
>> +for the remaining pages.
>> +
>> endif # MEMORY_HOTPLUG
>>
>> config ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
>> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
>> index 07c99b0cc371..f36aec1f7626 100644
>> --- a/mm/memory_hotplug.c
>> +++ b/mm/memory_hotplug.c
>> @@ -1252,15 +1252,17 @@ static inline bool
>> arch_supports_memmap_on_memory(unsigned long size)
>> {
>> unsigned long nr_vmemmap_pages = size >> PAGE_SHIFT;
>> unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
>> -unsigned long remaining_size = size - vmemmap_size;
>>
>> -return IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
>> -IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT));
>> +return IS_ALIGNED(vmemmap_size, PMD_SIZE);
>> }
>> #endif
>>
>> static bool mhp_supports_memmap_on_memory(unsigned long size)
>> {
>> +unsigned long nr_vmemmap_pages = size >> PAGE_SHIFT;
>> +unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
>> +unsigned long remaining_size = size - vmemmap_size;
>> +
>> /*
>> * Besides having arch support and the feature enabled at runtime, we
>> * need a few more assumptions to hold true:
>> @@ -1287,9 +1289,30 @@ static bool mhp_supports_memmap_on_memory(unsigned
>> long size)
>> * altmap as an alternative source of memory, and we do not
>> exactly
>> * populate a single PMD.
>> */
>> -return mhp_memmap_on_memory() &&
>> -size == memory_block_size_bytes() &&
>> -arch_supports_memmap_on_memory(size);
>> +if (!mhp_memmap_on_memory() || size != memory_block_size_bytes())
>> +return false;
>> + /*
>> + * Without page reservation remaining pages should be pageblock
>> aligned.
>> + */
>> +if (!IS_ENABLED(CONFIG_MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY) &&
>> +!IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT)))
>> +return false;
>> +
>> +return arch_supports_memmap_on_memory(size);
>> +}
>> +
>> +static inline unsigned long memory_block_align_base(unsigned long size)
>> +{
>> +if (IS_ENABLED(CONFIG_MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY)) {
>> +unsigned long align;
>> +unsigned long nr_vmemmap_pages = size >> PAGE_SHIFT;
>> +unsigned long vmemmap_size;
>> +
>> +vmemmap_size = (nr_vmemmap_pages * sizeof(struct page)) >>
>> PAGE_SHIFT;
>
> DIV_ROUND_UP()?
>
>
yes. Will update.
vmemmap_size = DIV_ROUND_UP(nr_vmemmap_pages * sizeof(struct
page), PAGE_SIZE);
-aneesh
Re: [PATCH v3 4/7] mm/hotplug: Allow pageblock alignment via altmap reservation
"Aneesh Kumar K.V" writes:
> Add a new kconfig option that can be selected if we want to allow
> pageblock alignment by reserving pages in the vmemmap altmap area.
> This implies we will be reserving some pages for every memoryblock
> This also allows the memmap on memory feature to be widely useful
> with different memory block size values.
>
> Signed-off-by: Aneesh Kumar K.V
> ---
> mm/Kconfig | 9 +++
> mm/memory_hotplug.c | 59 +
> 2 files changed, 58 insertions(+), 10 deletions(-)
>
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 932349271e28..88a1472b2086 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -570,6 +570,15 @@ config MHP_MEMMAP_ON_MEMORY
> depends on MEMORY_HOTPLUG && SPARSEMEM_VMEMMAP
> depends on ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
>
> +config MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY
> + bool "Allow Reserving pages for page block aligment"
> + depends on MHP_MEMMAP_ON_MEMORY
> + help
> + This option allows memmap on memory feature to be more useful
> + with different memory block sizes. This is achieved by marking some
> pages
> + in each memory block as reserved so that we can get page-block alignment
> + for the remaining pages.
> +
> endif # MEMORY_HOTPLUG
>
> config ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 07c99b0cc371..f36aec1f7626 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1252,15 +1252,17 @@ static inline bool
> arch_supports_memmap_on_memory(unsigned long size)
> {
> unsigned long nr_vmemmap_pages = size >> PAGE_SHIFT;
> unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
> - unsigned long remaining_size = size - vmemmap_size;
>
> - return IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
> - IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT));
> + return IS_ALIGNED(vmemmap_size, PMD_SIZE);
> }
> #endif
>
> static bool mhp_supports_memmap_on_memory(unsigned long size)
> {
> + unsigned long nr_vmemmap_pages = size >> PAGE_SHIFT;
> + unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
> + unsigned long remaining_size = size - vmemmap_size;
> +
> /*
>* Besides having arch support and the feature enabled at runtime, we
>* need a few more assumptions to hold true:
> @@ -1287,9 +1289,30 @@ static bool mhp_supports_memmap_on_memory(unsigned
> long size)
>* altmap as an alternative source of memory, and we do not
> exactly
>* populate a single PMD.
>*/
> - return mhp_memmap_on_memory() &&
> - size == memory_block_size_bytes() &&
> - arch_supports_memmap_on_memory(size);
> + if (!mhp_memmap_on_memory() || size != memory_block_size_bytes())
> + return false;
> + /*
> + * Without page reservation remaining pages should be pageblock
> aligned.
> + */
> + if (!IS_ENABLED(CONFIG_MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY) &&
> + !IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT)))
> + return false;
> +
> + return arch_supports_memmap_on_memory(size);
> +}
> +
> +static inline unsigned long memory_block_align_base(unsigned long size)
> +{
> + if (IS_ENABLED(CONFIG_MHP_RESERVE_PAGES_MEMMAP_ON_MEMORY)) {
> + unsigned long align;
> + unsigned long nr_vmemmap_pages = size >> PAGE_SHIFT;
> + unsigned long vmemmap_size;
> +
> + vmemmap_size = (nr_vmemmap_pages * sizeof(struct page)) >>
> PAGE_SHIFT;
DIV_ROUND_UP()?
> + align = pageblock_align(vmemmap_size) - vmemmap_size;
> + return align;
> + } else
> + return 0;
> }
>
> /*
> @@ -1302,7 +1325,11 @@ int __ref add_memory_resource(int nid, struct resource
> *res, mhp_t mhp_flags)
> {
> struct mhp_params params = { .pgprot = pgprot_mhp(PAGE_KERNEL) };
> enum memblock_flags memblock_flags = MEMBLOCK_NONE;
> - struct vmem_altmap mhp_altmap = {};
> + struct vmem_altmap mhp_altmap = {
> + .base_pfn = PHYS_PFN(res->start),
> + .end_pfn = PHYS_PFN(res->end),
> + .reserve = memory_block_align_base(resource_size(res)),
> + };
> struct memory_group *group = NULL;
> u64 start, size;
> bool new_node = false;
> @@ -1347,8 +1374,7 @@ 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 = PHYS_PFN(size);
> - mhp_altmap.base_pfn = PHYS_PFN(start);
> + mhp_altmap.free = PHYS_PFN(size) - mhp_altmap.reserve;
> params.altmap = _altmap;
> }
> /* fallback to not using altmap */
> @@ -1360,7
