[PATCH 08/11] hugetlb: Remove VMEMMAP_SYNCHRONIZE_RCU

Kiryl Shutsemau
2025-12-05T19:44:09Z

Fake heads no longer exist, so there is no reason to synchronize them
with page_ref_add_unless().

Remove the flag and the synchronization with synchronize_rcu() that is
gated by it.

Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
---
mm/hugetlb_vmemmap.c | 20 ++++----------------
1 file changed, 4 insertions(+), 16 deletions(-)

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 2543bdbcae20..0f142e4eafb9 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -48,8 +48,6 @@ struct vmemmap_remap_walk {
#define VMEMMAP_SPLIT_NO_TLB_FLUSH BIT(0)
/* Skip the TLB flush when we remap the PTE */
#define VMEMMAP_REMAP_NO_TLB_FLUSH BIT(1)
-/* synchronize_rcu() to avoid writes from page_ref_add_unless() */
-#define VMEMMAP_SYNCHRONIZE_RCU BIT(2)
unsigned long flags;
};

@@ -423,9 +421,6 @@ static int __hugetlb_vmemmap_restore_folio(const struct hstate *h,
if (!folio_test_hugetlb_vmemmap_optimized(folio))
return 0;

- if (flags & VMEMMAP_SYNCHRONIZE_RCU)
- synchronize_rcu();
-
vmemmap_start = (unsigned long)folio;
vmemmap_end = vmemmap_start + hugetlb_vmemmap_size(h);

@@ -457,7 +452,7 @@ static int __hugetlb_vmemmap_restore_folio(const struct hstate *h,
*/
int hugetlb_vmemmap_restore_folio(const struct hstate *h, struct folio *folio)
{
- return __hugetlb_vmemmap_restore_folio(h, folio, VMEMMAP_SYNCHRONIZE_RCU);
+ return __hugetlb_vmemmap_restore_folio(h, folio, 0);
}

/**
@@ -480,14 +475,11 @@ long hugetlb_vmemmap_restore_folios(const struct hstate *h,
struct folio *folio, *t_folio;
long restored = 0;
long ret = 0;
- unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH | VMEMMAP_SYNCHRONIZE_RCU;
+ unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH;

list_for_each_entry_safe(folio, t_folio, folio_list, lru) {
if (folio_test_hugetlb_vmemmap_optimized(folio)) {
ret = __hugetlb_vmemmap_restore_folio(h, folio, flags);
- /* only need to synchronize_rcu() once for each batch */
- flags &= ~VMEMMAP_SYNCHRONIZE_RCU;
-
if (ret)
break;
restored++;
@@ -558,8 +550,6 @@ static int __hugetlb_vmemmap_optimize_folio(struct hstate *h,

static_branch_inc(&hugetlb_optimize_vmemmap_key);

- if (flags & VMEMMAP_SYNCHRONIZE_RCU)
- synchronize_rcu();
/*
* Very Subtle
* If VMEMMAP_REMAP_NO_TLB_FLUSH is set, TLB flushing is not performed
@@ -621,7 +611,7 @@ void hugetlb_vmemmap_optimize_folio(struct hstate *h, struct folio *folio)
{
LIST_HEAD(vmemmap_pages);

- __hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, VMEMMAP_SYNCHRONIZE_RCU);
+ __hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, 0);
free_vmemmap_page_list(&vmemmap_pages);
}

@@ -649,7 +639,7 @@ static void __hugetlb_vmemmap_optimize_folios(struct hstate *h,
struct folio *folio;
int nr_to_optimize;
LIST_HEAD(vmemmap_pages);
- unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH | VMEMMAP_SYNCHRONIZE_RCU;
+ unsigned long flags = VMEMMAP_REMAP_NO_TLB_FLUSH;

nr_to_optimize = 0;
list_for_each_entry(folio, folio_list, lru) {
@@ -702,8 +692,6 @@ static void __hugetlb_vmemmap_optimize_folios(struct hstate *h,
int ret;

ret = __hugetlb_vmemmap_optimize_folio(h, folio, &vmemmap_pages, flags);
- /* only need to synchronize_rcu() once for each batch */
- flags &= ~VMEMMAP_SYNCHRONIZE_RCU;

/*
* Pages to be freed may have been accumulated. If we
--
2.51.2