[PATCH v8 8/8] hugetlb: batch TLB flushes when restoring vmemmap

Mike Kravetz
2023-10-19T02:33:05Z

Update the internal hugetlb restore vmemmap code path such that TLB
flushing can be batched. Use the existing mechanism of passing the
VMEMMAP_REMAP_NO_TLB_FLUSH flag to indicate flushing should not be
performed for individual pages. The routine hugetlb_vmemmap_restore_folios
is the only user of this new mechanism, and it will perform a global
flush after all vmemmap is restored.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
---
mm/hugetlb_vmemmap.c | 39 ++++++++++++++++++++++++---------------
1 file changed, 24 insertions(+), 15 deletions(-)

diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 9df350372046..d2999c303031 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -461,18 +461,19 @@ static int alloc_vmemmap_page_list(unsigned long start, unsigned long end,
* @end: end address of the vmemmap virtual address range that we want to
* remap.
* @reuse: reuse address.
+ * @flags: modifications to vmemmap_remap_walk flags
*
* Return: %0 on success, negative error code otherwise.
*/
static int vmemmap_remap_alloc(unsigned long start, unsigned long end,
- unsigned long reuse)
+ unsigned long reuse, unsigned long flags)
{
LIST_HEAD(vmemmap_pages);
struct vmemmap_remap_walk walk = {
.remap_pte = vmemmap_restore_pte,
.reuse_addr = reuse,
.vmemmap_pages = &vmemmap_pages,
- .flags = 0,
+ .flags = flags,
};

/* See the comment in the vmemmap_remap_free(). */
@@ -494,17 +495,7 @@ EXPORT_SYMBOL(hugetlb_optimize_vmemmap_key);
static bool vmemmap_optimize_enabled = IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON);
core_param(hugetlb_free_vmemmap, vmemmap_optimize_enabled, bool, 0);

-/**
- * hugetlb_vmemmap_restore - restore previously optimized (by
- * hugetlb_vmemmap_optimize()) vmemmap pages which
- * will be reallocated and remapped.
- * @h: struct hstate.
- * @head: the head page whose vmemmap pages will be restored.
- *
- * Return: %0 if @head's vmemmap pages have been reallocated and remapped,
- * negative error code otherwise.
- */
-int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head)
+static int __hugetlb_vmemmap_restore(const struct hstate *h, struct page *head, unsigned long flags)
{
int ret;
unsigned long vmemmap_start = (unsigned long)head, vmemmap_end;
@@ -525,7 +516,7 @@ int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head)
* When a HugeTLB page is freed to the buddy allocator, previously
* discarded vmemmap pages must be allocated and remapping.
*/
- ret = vmemmap_remap_alloc(vmemmap_start, vmemmap_end, vmemmap_reuse);
+ ret = vmemmap_remap_alloc(vmemmap_start, vmemmap_end, vmemmap_reuse, flags);
if (!ret) {
ClearHPageVmemmapOptimized(head);
static_branch_dec(&hugetlb_optimize_vmemmap_key);
@@ -534,6 +525,21 @@ int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head)
return ret;
}

+/**
+ * hugetlb_vmemmap_restore - restore previously optimized (by
+ * hugetlb_vmemmap_optimize()) vmemmap pages which
+ * will be reallocated and remapped.
+ * @h: struct hstate.
+ * @head: the head page whose vmemmap pages will be restored.
+ *
+ * Return: %0 if @head's vmemmap pages have been reallocated and remapped,
+ * negative error code otherwise.
+ */
+int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head)
+{
+ return __hugetlb_vmemmap_restore(h, head, 0);
+}
+
/**
* hugetlb_vmemmap_restore_folios - restore vmemmap for every folio on the list.
* @h: hstate.
@@ -557,7 +563,8 @@ long hugetlb_vmemmap_restore_folios(const struct hstate *h,

list_for_each_entry_safe(folio, t_folio, folio_list, lru) {
if (folio_test_hugetlb_vmemmap_optimized(folio)) {
- ret = hugetlb_vmemmap_restore(h, &folio->page);
+ ret = __hugetlb_vmemmap_restore(h, &folio->page,
+ VMEMMAP_REMAP_NO_TLB_FLUSH);
if (ret)
break;
restored++;
@@ -567,6 +574,8 @@ long hugetlb_vmemmap_restore_folios(const struct hstate *h,
list_move(&folio->lru, non_hvo_folios);
}

+ if (restored)
+ flush_tlb_all();
if (!ret)
ret = restored;
return ret;
--
2.41.0