[PATCH 5/5] hugetlb: Add hugetlb_dynamic_pool sysctl

[Adam Litke <agl@us.ibm.com>]

Allowing the hugetlb pool to grow dynamically changes the semantics of the
system by permitting more system memory to be used for huge pages than has
been explicitly dedicated to the pool.

This patch introduces a sysctl which must be enabled to turn on the dynamic
pool resizing feature.  This will avoid an involuntary change in behavior.

When hugetlb pool growth is enabled via the hugetlb_dynamic_pool sysctl, an
upper-bound on huge page allocation can be set by constraining the size of
the hugetlb filesystem via the 'size' mount option.

Signed-off-by: Adam Litke <agl@us.ibm.com>
Acked-by: Andy Whitcroft <apw@shadowen.org>
---

 include/linux/hugetlb.h |    1 +
 kernel/sysctl.c         |    8 ++++++++
 mm/hugetlb.c            |    5 +++++
 3 files changed, 14 insertions(+), 0 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index e6a71c8..cec45db 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -33,6 +33,7 @@ void hugetlb_unreserve_pages(struct inode *inode, long offset, long freed);
 
 extern unsigned long max_huge_pages;
 extern unsigned long hugepages_treat_as_movable;
+extern int hugetlb_dynamic_pool;
 extern const unsigned long hugetlb_zero, hugetlb_infinity;
 extern int sysctl_hugetlb_shm_group;
 
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 8bdb8c0..fd60a5e 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -879,6 +879,14 @@ static ctl_table vm_table[] = {
 		.mode		= 0644,
 		.proc_handler	= &hugetlb_treat_movable_handler,
 	},
+	{
+		.ctl_name	= CTL_UNNUMBERED,
+		.procname	= "hugetlb_dynamic_pool",
+		.data		= &hugetlb_dynamic_pool,
+		.maxlen		= sizeof(hugetlb_dynamic_pool),
+		.mode		= 0644,
+		.proc_handler	= &proc_dointvec,
+	},
 #endif
 	{
 		.ctl_name	= VM_LOWMEM_RESERVE_RATIO,
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 0cedcd0..caef721 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -31,6 +31,7 @@ static unsigned int surplus_huge_pages_node[MAX_NUMNODES];
 static unsigned long unused_surplus_pages;
 static gfp_t htlb_alloc_mask = GFP_HIGHUSER;
 unsigned long hugepages_treat_as_movable;
+int hugetlb_dynamic_pool;
 
 /*
  * Protects updates to hugepage_freelists, nr_huge_pages, and free_huge_pages
@@ -189,6 +190,10 @@ static struct page *alloc_buddy_huge_page(struct vm_area_struct *vma,
 {
 	struct page *page;
 
+	/* Check if the dynamic pool is enabled */
+	if (!hugetlb_dynamic_pool)
+		return NULL;
+
 	/* Check we remain within limits if 1 huge page is allocated */
 	if (!within_locked_vm_limits(1))
 		return NULL;

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