[PATCH v8 4/8] hugetlb: perform vmemmap restoration on a list of pages

Mike Kravetz
2023-10-19T02:32:29Z

The routine update_and_free_pages_bulk already performs vmemmap
restoration on the list of hugetlb pages in a separate step. In
preparation for more functionality to be added in this step, create a
new routine hugetlb_vmemmap_restore_folios() that will restore
vmemmap for a list of folios.

This new routine must provide sufficient feedback about errors and
actual restoration performed so that update_and_free_pages_bulk can
perform optimally.

Special care must be taken when encountering an error from
hugetlb_vmemmap_restore_folios. We want to continue making as much
forward progress as possible. A new routine bulk_vmemmap_restore_error
handles this specific situation.

Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
Reviewed-by: Muchun Song <songmuchun@bytedance.com>
---
mm/hugetlb.c | 99 +++++++++++++++++++++++++++++++-------------
mm/hugetlb_vmemmap.c | 38 +++++++++++++++++
mm/hugetlb_vmemmap.h | 11 +++++
3 files changed, 120 insertions(+), 28 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 8b171f866d0a..cf834bb7f820 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1859,50 +1859,93 @@ static void update_and_free_hugetlb_folio(struct hstate *h, struct folio *folio,
schedule_work(&free_hpage_work);
}

-static void update_and_free_pages_bulk(struct hstate *h, struct list_head *list)
+static void bulk_vmemmap_restore_error(struct hstate *h,
+ struct list_head *folio_list,
+ struct list_head *non_hvo_folios)
{
struct folio *folio, *t_folio;
- bool clear_dtor = false;

- /*
- * First allocate required vmemmmap (if necessary) for all folios on
- * list. If vmemmap can not be allocated, we can not free folio to
- * lower level allocator, so add back as hugetlb surplus page.
- * add_hugetlb_folio() removes the page from THIS list.
- * Use clear_dtor to note if vmemmap was successfully allocated for
- * ANY page on the list.
- */
- list_for_each_entry_safe(folio, t_folio, list, lru) {
- if (folio_test_hugetlb_vmemmap_optimized(folio)) {
+ if (!list_empty(non_hvo_folios)) {
+ /*
+ * Free any restored hugetlb pages so that restore of the
+ * entire list can be retried.
+ * The idea is that in the common case of ENOMEM errors freeing
+ * hugetlb pages with vmemmap we will free up memory so that we
+ * can allocate vmemmap for more hugetlb pages.
+ */
+ list_for_each_entry_safe(folio, t_folio, non_hvo_folios, lru) {
+ list_del(&folio->lru);
+ spin_lock_irq(&hugetlb_lock);
+ __clear_hugetlb_destructor(h, folio);
+ spin_unlock_irq(&hugetlb_lock);
+ update_and_free_hugetlb_folio(h, folio, false);
+ cond_resched();
+ }
+ } else {
+ /*
+ * In the case where there are no folios which can be
+ * immediately freed, we loop through the list trying to restore
+ * vmemmap individually in the hope that someone elsewhere may
+ * have done something to cause success (such as freeing some
+ * memory). If unable to restore a hugetlb page, the hugetlb
+ * page is made a surplus page and removed from the list.
+ * If are able to restore vmemmap and free one hugetlb page, we
+ * quit processing the list to retry the bulk operation.
+ */
+ list_for_each_entry_safe(folio, t_folio, folio_list, lru)
if (hugetlb_vmemmap_restore(h, &folio->page)) {
+ list_del(&folio->lru);
spin_lock_irq(&hugetlb_lock);
add_hugetlb_folio(h, folio, true);
spin_unlock_irq(&hugetlb_lock);
- } else
- clear_dtor = true;
- }
+ } else {
+ list_del(&folio->lru);
+ spin_lock_irq(&hugetlb_lock);
+ __clear_hugetlb_destructor(h, folio);
+ spin_unlock_irq(&hugetlb_lock);
+ update_and_free_hugetlb_folio(h, folio, false);
+ cond_resched();
+ break;
+ }
}
+}
+
+static void update_and_free_pages_bulk(struct hstate *h,
+ struct list_head *folio_list)
+{
+ long ret;
+ struct folio *folio, *t_folio;
+ LIST_HEAD(non_hvo_folios);

/*
- * If vmemmmap allocation was performed on any folio above, take lock
- * to clear destructor of all folios on list. This avoids the need to
- * lock/unlock for each individual folio.
- * The assumption is vmemmap allocation was performed on all or none
- * of the folios on the list. This is true expect in VERY rare cases.
+ * First allocate required vmemmmap (if necessary) for all folios.
+ * Carefully handle errors and free up any available hugetlb pages
+ * in an effort to make forward progress.
*/
- if (clear_dtor) {
+retry:
+ ret = hugetlb_vmemmap_restore_folios(h, folio_list, &non_hvo_folios);
+ if (ret < 0) {
+ bulk_vmemmap_restore_error(h, folio_list, &non_hvo_folios);
+ goto retry;
+ }
+
+ /*
+ * At this point, list should be empty, ret should be >= 0 and there
+ * should only be pages on the non_hvo_folios list.
+ * Do note that the non_hvo_folios list could be empty.
+ * Without HVO enabled, ret will be 0 and there is no need to call
+ * __clear_hugetlb_destructor as this was done previously.
+ */
+ VM_WARN_ON(!list_empty(folio_list));
+ VM_WARN_ON(ret < 0);
+ if (!list_empty(&non_hvo_folios) && ret) {
spin_lock_irq(&hugetlb_lock);
- list_for_each_entry(folio, list, lru)
+ list_for_each_entry(folio, &non_hvo_folios, lru)
__clear_hugetlb_destructor(h, folio);
spin_unlock_irq(&hugetlb_lock);
}

- /*
- * Free folios back to low level allocators. vmemmap and destructors
- * were taken care of above, so update_and_free_hugetlb_folio will
- * not need to take hugetlb lock.
- */
- list_for_each_entry_safe(folio, t_folio, list, lru) {
+ list_for_each_entry_safe(folio, t_folio, &non_hvo_folios, lru) {
update_and_free_hugetlb_folio(h, folio, false);
cond_resched();
}
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 4558b814ffab..77f44b81ff01 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -480,6 +480,44 @@ int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head)
return ret;
}

+/**
+ * hugetlb_vmemmap_restore_folios - restore vmemmap for every folio on the list.
+ * @h: hstate.
+ * @folio_list: list of folios.
+ * @non_hvo_folios: Output list of folios for which vmemmap exists.
+ *
+ * Return: number of folios for which vmemmap was restored, or an error code
+ * if an error was encountered restoring vmemmap for a folio.
+ * Folios that have vmemmap are moved to the non_hvo_folios
+ * list. Processing of entries stops when the first error is
+ * encountered. The folio that experienced the error and all
+ * non-processed folios will remain on folio_list.
+ */
+long hugetlb_vmemmap_restore_folios(const struct hstate *h,
+ struct list_head *folio_list,
+ struct list_head *non_hvo_folios)
+{
+ struct folio *folio, *t_folio;
+ long restored = 0;
+ long ret = 0;
+
+ 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);
+ if (ret)
+ break;
+ restored++;
+ }
+
+ /* Add non-optimized folios to output list */
+ list_move(&folio->lru, non_hvo_folios);
+ }
+
+ if (!ret)
+ ret = restored;
+ return ret;
+}
+
/* Return true iff a HugeTLB whose vmemmap should and can be optimized. */
static bool vmemmap_should_optimize(const struct hstate *h, const struct page *head)
{
diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h
index c512e388dbb4..a0dcf49f46ba 100644
--- a/mm/hugetlb_vmemmap.h
+++ b/mm/hugetlb_vmemmap.h
@@ -19,6 +19,9 @@

#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head);
+long hugetlb_vmemmap_restore_folios(const struct hstate *h,
+ struct list_head *folio_list,
+ struct list_head *non_hvo_folios);
void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head);
void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head *folio_list);

@@ -45,6 +48,14 @@ static inline int hugetlb_vmemmap_restore(const struct hstate *h, struct page *h
return 0;
}

+static long hugetlb_vmemmap_restore_folios(const struct hstate *h,
+ struct list_head *folio_list,
+ struct list_head *non_hvo_folios)
+{
+ list_splice_init(folio_list, non_hvo_folios);
+ return 0;
+}
+
static inline void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
{
}
--
2.41.0