Documentation/admin-guide/sysctl/vm.rst | 17 +++++++++++++++++ include/linux/hugetlb.h | 3 ++- mm/hugetlb.c | 11 +++++++++++ 3 files changed, 30 insertions(+), 1 deletion(-)
This reintroduces a concept removed by
commit d6cb41cc44c6 ("mm, hugetlb: remove hugepages_treat_as_movable sysctl")
This sysctl provides some flexibility between multiple ZONE_MOVABLE
use cases
1) onlining memory in ZONE_MOVABLE to maintain hotplug compatibility
2) onlining memory in ZONE_MOVABLE to make hugepage allocate reliable
When ZONE_MOVABLE is used to make huge page allocation more reliable,
disallowing gigantic pages memory in this region is pointless. If
hotplug is not a requirement, we can loosen the restrictions to allow
1GB gigantic pages in ZONE_MOVABLE.
Since 1GB can be difficult to migrate / has impacts on compaction /
defragmentation, we don't enable this by default. Notably, 1GB pages
can only be migrated if another 1GB page is available - so hot-unplug
will fail if such a page cannot be found.
However, since there are scenarios where gigantic pages are migratable,
we should allow use of these on movable regions.
Note: Boot-time CMA is not possible for driver-managed hotplug memory,
as CMA requires the memory to be registered as SystemRAM at boot time.
Additionally, 1GB huge pages are not supported by THP.
Cc: David Hildenbrand <david@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Alexandru Moise <00moses.alexander00@gmail.com>
Suggested-by: David Rientjes <rientjes@google.com>
Signed-off-by: Gregory Price <gourry@gourry.net>
Link: https://lore.kernel.org/all/20180201193132.Hk7vI_xaU%25akpm@linux-foundation.org/
---
Documentation/admin-guide/sysctl/vm.rst | 17 +++++++++++++++++
include/linux/hugetlb.h | 3 ++-
mm/hugetlb.c | 11 +++++++++++
3 files changed, 30 insertions(+), 1 deletion(-)
---
v2: changelog updates
diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
index b325bfbc2611..fe3982604b1f 100644
--- a/Documentation/admin-guide/sysctl/vm.rst
+++ b/Documentation/admin-guide/sysctl/vm.rst
@@ -54,6 +54,7 @@ Currently, these files are in /proc/sys/vm:
- mmap_min_addr
- mmap_rnd_bits
- mmap_rnd_compat_bits
+- movable_gigantic_pages
- nr_hugepages
- nr_hugepages_mempolicy
- nr_overcommit_hugepages
@@ -623,6 +624,22 @@ This value can be changed after boot using the
/proc/sys/vm/mmap_rnd_compat_bits tunable
+movable_gigantic_pages
+======================
+
+This parameter controls whether gigantic pages may be allocated from
+ZONE_MOVABLE. If set to non-zero, gigantic hugepages can be allocated
+from ZONE_MOVABLE. ZONE_MOVABLE memory may be created via the kernel
+boot parameter `kernelcore` or via memory hotplug as discussed in
+Documentation/admin-guide/mm/memory-hotplug.rst.
+
+Support may depend on specific architecture.
+
+Note that using ZONE_MOVABLE gigantic pages may make features like
+memory hotremove more unreliable, as migrating gigantic pages is more
+difficult due to needing larger amounts of phyiscally contiguous memory.
+
+
nr_hugepages
============
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index eb21619206af..451ede7b97dd 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -172,6 +172,7 @@ bool hugetlbfs_pagecache_present(struct hstate *h,
struct address_space *hugetlb_folio_mapping_lock_write(struct folio *folio);
+extern int movable_gigantic_pages __read_mostly;
extern int sysctl_hugetlb_shm_group;
extern struct list_head huge_boot_pages[MAX_NUMNODES];
@@ -916,7 +917,7 @@ static inline bool hugepage_movable_supported(struct hstate *h)
if (!hugepage_migration_supported(h))
return false;
- if (hstate_is_gigantic(h))
+ if (hstate_is_gigantic(h) && !movable_gigantic_pages)
return false;
return true;
}
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 5b77fef5c4fd..c6363dad1e92 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -54,6 +54,8 @@
#include "hugetlb_cma.h"
#include <linux/page-isolation.h>
+int movable_gigantic_pages;
+
int hugetlb_max_hstate __read_mostly;
unsigned int default_hstate_idx;
struct hstate hstates[HUGE_MAX_HSTATE];
@@ -5208,6 +5210,15 @@ static const struct ctl_table hugetlb_table[] = {
.mode = 0644,
.proc_handler = hugetlb_overcommit_handler,
},
+#ifdef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION
+ {
+ .procname = "movable_gigantic_pages",
+ .data = &movable_gigantic_pages,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = proc_dointvec,
+ },
+#endif
};
static void __init hugetlb_sysctl_init(void)
--
2.51.1On 11/21/25 20:27, Gregory Price wrote:
> This reintroduces a concept removed by
> commit d6cb41cc44c6 ("mm, hugetlb: remove hugepages_treat_as_movable sysctl")
>
> This sysctl provides some flexibility between multiple ZONE_MOVABLE
> use cases
>
> 1) onlining memory in ZONE_MOVABLE to maintain hotplug compatibility
> 2) onlining memory in ZONE_MOVABLE to make hugepage allocate reliable
>
> When ZONE_MOVABLE is used to make huge page allocation more reliable,
> disallowing gigantic pages memory in this region is pointless. If
> hotplug is not a requirement, we can loosen the restrictions to allow
> 1GB gigantic pages in ZONE_MOVABLE.
>
> Since 1GB can be difficult to migrate / has impacts on compaction /
> defragmentation, we don't enable this by default. Notably, 1GB pages
> can only be migrated if another 1GB page is available - so hot-unplug
> will fail if such a page cannot be found.
>
> However, since there are scenarios where gigantic pages are migratable,
> we should allow use of these on movable regions.
>
> Note: Boot-time CMA is not possible for driver-managed hotplug memory,
> as CMA requires the memory to be registered as SystemRAM at boot time.
> Additionally, 1GB huge pages are not supported by THP.
>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Mel Gorman <mgorman@suse.de>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Alexandru Moise <00moses.alexander00@gmail.com>
> Suggested-by: David Rientjes <rientjes@google.com>
> Signed-off-by: Gregory Price <gourry@gourry.net>
> Link: https://lore.kernel.org/all/20180201193132.Hk7vI_xaU%25akpm@linux-foundation.org/
> ---
> Documentation/admin-guide/sysctl/vm.rst | 17 +++++++++++++++++
> include/linux/hugetlb.h | 3 ++-
> mm/hugetlb.c | 11 +++++++++++
> 3 files changed, 30 insertions(+), 1 deletion(-)
>
> ---
> v2: changelog updates
>
>
> diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst
> index b325bfbc2611..fe3982604b1f 100644
> --- a/Documentation/admin-guide/sysctl/vm.rst
> +++ b/Documentation/admin-guide/sysctl/vm.rst
> @@ -54,6 +54,7 @@ Currently, these files are in /proc/sys/vm:
> - mmap_min_addr
> - mmap_rnd_bits
> - mmap_rnd_compat_bits
> +- movable_gigantic_pages
> - nr_hugepages
> - nr_hugepages_mempolicy
> - nr_overcommit_hugepages
> @@ -623,6 +624,22 @@ This value can be changed after boot using the
> /proc/sys/vm/mmap_rnd_compat_bits tunable
>
>
> +movable_gigantic_pages
> +======================
> +
> +This parameter controls whether gigantic pages may be allocated from
> +ZONE_MOVABLE. If set to non-zero, gigantic hugepages can be allocated
"gigantic pages" or "gigantic hugetlb pages"
> +from ZONE_MOVABLE. ZONE_MOVABLE memory may be created via the kernel
> +boot parameter `kernelcore` or via memory hotplug as discussed in
> +Documentation/admin-guide/mm/memory-hotplug.rst.
> +
> +Support may depend on specific architecture.
> +
> +Note that using ZONE_MOVABLE gigantic pages may make features like
> +memory hotremove more unreliable, as migrating gigantic pages is more
> +difficult due to needing larger amounts of phyiscally contiguous memory.
s/phyiscally/physically/ ?
Can we also reference this parameter here from
Documentation/admin-guide/mm/memory-hotplug.rst?
In particular, there we also talk about gigantic pages and the
interaction with ZONE_MOVABLE:
"
- Gigantic pages are unmovable, resulting in user space consuming a
lot of unmovable memory.
- Huge pages are unmovable when an architectures does not support huge
page migration, resulting in a similar issue as with gigantic pages.
"
And then later, we talk about "Even with ZONE_MOVABLE, there are some
corner cases where offlining a memory
block might fail:" where this should be spelled out as well.
--
Cheers
David
On Tue, Nov 25, 2025 at 11:24:24AM +0100, David Hildenbrand (Red Hat) wrote: > On 11/21/25 20:27, Gregory Price wrote: > > Can we also reference this parameter here from > Documentation/admin-guide/mm/memory-hotplug.rst? > Good call > In particular, there we also talk about gigantic pages and the interaction > with ZONE_MOVABLE: > > " > - Gigantic pages are unmovable, resulting in user space consuming a > lot of unmovable memory. > > - Huge pages are unmovable when an architectures does not support huge > page migration, resulting in a similar issue as with gigantic pages. > " > > And then later, we talk about "Even with ZONE_MOVABLE, there are some corner > cases where offlining a memory > block might fail:" where this should be spelled out as well. > I will take a look, thank you! > -- > Cheers > > David
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