[RFC PATCH v2 24/51] mm: hugetlb: Add option to create new subpool without using surplus

[Ackerley Tng <ackerleytng@google.com>]

__hugetlb_acct_memory() today does more than just memory
accounting. When there's insufficient HugeTLB pages,
__hugetlb_acct_memory() will attempt to get surplus pages.

This change adds a flag to disable getting surplus pages if there are
insufficient HugeTLB pages.

Signed-off-by: Ackerley Tng <ackerleytng@google.com>
Change-Id: Id79fdeaa236b4fed38fc3c20482b03fff729198f
---
 fs/hugetlbfs/inode.c    |  2 +-
 include/linux/hugetlb.h |  2 +-
 mm/hugetlb.c            | 77 +++++++++++++++++++++++++++++++----------
 3 files changed, 61 insertions(+), 20 deletions(-)

diff --git a/fs/hugetlbfs/inode.c b/fs/hugetlbfs/inode.c
index e4de5425838d..609a88950354 100644
--- a/fs/hugetlbfs/inode.c
+++ b/fs/hugetlbfs/inode.c
@@ -1424,7 +1424,7 @@ hugetlbfs_fill_super(struct super_block *sb, struct fs_context *fc)
 	if (ctx->max_hpages != -1 || ctx->min_hpages != -1) {
 		sbinfo->spool = hugepage_new_subpool(ctx->hstate,
 						     ctx->max_hpages,
-						     ctx->min_hpages);
+						     ctx->min_hpages, true);
 		if (!sbinfo->spool)
 			goto out_free;
 	}
diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 8ba941d88956..c59264391c33 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -116,7 +116,7 @@ extern int hugetlb_max_hstate __read_mostly;
 	for ((h) = hstates; (h) < &hstates[hugetlb_max_hstate]; (h)++)
 
 struct hugepage_subpool *hugepage_new_subpool(struct hstate *h, long max_hpages,
-						long min_hpages);
+					      long min_hpages, bool use_surplus);
 void hugepage_put_subpool(struct hugepage_subpool *spool);
 
 void hugetlb_dup_vma_private(struct vm_area_struct *vma);
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 5b088fe002a2..d22c5a8fd441 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -115,6 +115,7 @@ static int num_fault_mutexes __ro_after_init;
 struct mutex *hugetlb_fault_mutex_table __ro_after_init;
 
 /* Forward declaration */
+static int __hugetlb_acct_memory(struct hstate *h, long delta, bool use_surplus);
 static int hugetlb_acct_memory(struct hstate *h, long delta);
 static void hugetlb_vma_lock_free(struct vm_area_struct *vma);
 static void hugetlb_vma_lock_alloc(struct vm_area_struct *vma);
@@ -162,7 +163,7 @@ static inline void unlock_or_release_subpool(struct hugepage_subpool *spool,
 }
 
 struct hugepage_subpool *hugepage_new_subpool(struct hstate *h, long max_hpages,
-						long min_hpages)
+					      long min_hpages, bool use_surplus)
 {
 	struct hugepage_subpool *spool;
 
@@ -176,7 +177,8 @@ struct hugepage_subpool *hugepage_new_subpool(struct hstate *h, long max_hpages,
 	spool->hstate = h;
 	spool->min_hpages = min_hpages;
 
-	if (min_hpages != -1 && hugetlb_acct_memory(h, min_hpages)) {
+	if (min_hpages != -1 &&
+	    __hugetlb_acct_memory(h, min_hpages, use_surplus)) {
 		kfree(spool);
 		return NULL;
 	}
@@ -2382,35 +2384,64 @@ static nodemask_t *policy_mbind_nodemask(gfp_t gfp)
 	return NULL;
 }
 
-/*
- * Increase the hugetlb pool such that it can accommodate a reservation
- * of size 'delta'.
+/**
+ * hugetlb_hstate_reserve_pages() - Reserve @requested number of hugetlb pages
+ * from hstate @h.
+ *
+ * @h: the hstate to reserve from.
+ * @requested: number of hugetlb pages to reserve.
+ *
+ * If there are insufficient available hugetlb pages, no reservations are made.
+ *
+ * Return: the number of surplus pages required to meet the @requested number of
+ *         hugetlb pages.
  */
-static int gather_surplus_pages(struct hstate *h, long delta)
+static int hugetlb_hstate_reserve_pages(struct hstate *h, long requested)
+	__must_hold(&hugetlb_lock)
+{
+	long needed;
+
+	needed = (h->resv_huge_pages + requested) - h->free_huge_pages;
+	if (needed <= 0) {
+		h->resv_huge_pages += requested;
+		return 0;
+	}
+
+	return needed;
+}
+
+/**
+ * gather_surplus_pages() - Increase the hugetlb pool such that it can
+ * accommodate a reservation of size @requested.
+ *
+ * @h: the hstate in concern.
+ * @requested: The requested number of hugetlb pages.
+ * @needed: The number of hugetlb pages the pool needs to be increased by, based
+ *          on current number of reservations and free hugetlb pages.
+ *
+ * Return: 0 if successful or negative error otherwise.
+ */
+static int gather_surplus_pages(struct hstate *h, long requested, long needed)
 	__must_hold(&hugetlb_lock)
 {
 	LIST_HEAD(surplus_list);
 	struct folio *folio, *tmp;
 	int ret;
 	long i;
-	long needed, allocated;
+	long allocated;
 	bool alloc_ok = true;
 	int node;
 	nodemask_t *mbind_nodemask, alloc_nodemask;
 
+	if (needed == 0)
+		return 0;
+
 	mbind_nodemask = policy_mbind_nodemask(htlb_alloc_mask(h));
 	if (mbind_nodemask)
 		nodes_and(alloc_nodemask, *mbind_nodemask, cpuset_current_mems_allowed);
 	else
 		alloc_nodemask = cpuset_current_mems_allowed;
 
-	lockdep_assert_held(&hugetlb_lock);
-	needed = (h->resv_huge_pages + delta) - h->free_huge_pages;
-	if (needed <= 0) {
-		h->resv_huge_pages += delta;
-		return 0;
-	}
-
 	allocated = 0;
 
 	ret = -ENOMEM;
@@ -2448,7 +2479,7 @@ static int gather_surplus_pages(struct hstate *h, long delta)
 	 * because either resv_huge_pages or free_huge_pages may have changed.
 	 */
 	spin_lock_irq(&hugetlb_lock);
-	needed = (h->resv_huge_pages + delta) -
+	needed = (h->resv_huge_pages + requested) -
 			(h->free_huge_pages + allocated);
 	if (needed > 0) {
 		if (alloc_ok)
@@ -2469,7 +2500,7 @@ static int gather_surplus_pages(struct hstate *h, long delta)
 	 * before they are reserved.
 	 */
 	needed += allocated;
-	h->resv_huge_pages += delta;
+	h->resv_huge_pages += requested;
 	ret = 0;
 
 	/* Free the needed pages to the hugetlb pool */
@@ -5284,7 +5315,7 @@ unsigned long hugetlb_total_pages(void)
 	return nr_total_pages;
 }
 
-static int hugetlb_acct_memory(struct hstate *h, long delta)
+static int __hugetlb_acct_memory(struct hstate *h, long delta, bool use_surplus)
 {
 	int ret = -ENOMEM;
 
@@ -5316,7 +5347,12 @@ static int hugetlb_acct_memory(struct hstate *h, long delta)
 	 * above.
 	 */
 	if (delta > 0) {
-		if (gather_surplus_pages(h, delta) < 0)
+		long needed = hugetlb_hstate_reserve_pages(h, delta);
+
+		if (!use_surplus && needed > 0)
+			goto out;
+
+		if (gather_surplus_pages(h, delta, needed) < 0)
 			goto out;
 
 		if (delta > allowed_mems_nr(h)) {
@@ -5334,6 +5370,11 @@ static int hugetlb_acct_memory(struct hstate *h, long delta)
 	return ret;
 }
 
+static int hugetlb_acct_memory(struct hstate *h, long delta)
+{
+	return __hugetlb_acct_memory(h, delta, true);
+}
+
 static void hugetlb_vm_op_open(struct vm_area_struct *vma)
 {
 	struct resv_map *resv = vma_resv_map(vma);
-- 
2.49.0.1045.g170613ef41-goog