Re: [PATCH v4 4/8] hugetlb: perform vmemmap restoration on a list of pages
From: Muchun Song
Date: Fri Sep 22 2023 - 04:19:56 EST
On 2023/9/22 05:58, Mike Kravetz wrote:
On 09/21/23 17:31, Muchun Song wrote:
On 2023/9/21 09:12, Mike Kravetz wrote:
On 09/20/23 11:03, Muchun Song wrote:
On Sep 20, 2023, at 10:56, Muchun Song <muchun.song@xxxxxxxxx> wrote:
On Sep 20, 2023, at 04:57, Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote:
On 09/19/23 17:52, Muchun Song wrote:
On 2023/9/19 07:01, Mike Kravetz wrote:
+/**
+ * hugetlb_vmemmap_restore_folios - restore vmemmap for every folio on the list.
+ * @h: struct hstate.
+ * @folio_list: list of folios.
+ * @restored: Set to number of folios for which vmemmap was restored
+ * successfully if caller passes a non-NULL pointer.
+ *
+ * Return: %0 if vmemmap exists for all folios on the list. If an error is
+ * encountered restoring vmemmap for ANY folio, an error code
+ * will be returned to the caller. It is then the responsibility
+ * of the caller to check the hugetlb vmemmap optimized flag of
+ * each folio to determine if vmemmap was actually restored.
+ * Note that processing is stopped when first error is encountered.
+ */
+int hugetlb_vmemmap_restore_folios(const struct hstate *h,
+ struct list_head *folio_list,
+ unsigned long *restored)
How about changing parameter of @restored to a list_head type which
returns the non-optimized (previously) or vmemmap-restored-sucessful huge
pages?
In which case, the caller could traverse this returned list to free
them first like you have implemented in bulk_vmemmap_restore_enomem(),
it will be more efficient. The meaning of returned value should also
be changed accordingly since update_and_free_pages_bulk() wants to
whether there is a vmemmap-optimized huge page being restored sucessfully
to determine if it should clear hugetlb flag. So
hugetlb_vmemmap_restore_folios()
could return how many huge pages being restored successful, if a negative
number is returned meaning there is some error in the process of restoring
of vmemmap.
I had similar thoughts. An updated patch based on this approach is below.
When creating the patch, I discovered that using the function return code
for both number of vmemmap restored pages as well as error code was
unnecessary. Just checking !list_empty() of non-optimized pages tells us
if any were restored or could be freed.
I also thought about this. But there is a little different. If HVO
is disabled, we will always clear the hugetlb flag twice since the
list couldn't be empty, I thought it is an optimization for HVO-disabled
case.
From b79f6eeb7a11644830bddfc43d2219c149d26405 Mon Sep 17 00:00:00 2001
From: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Date: Sun, 10 Sep 2023 16:14:50 -0700
Subject: [PATCH] hugetlb: perform vmemmap restoration on a list of pages
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@xxxxxxxxxx>
---
mm/hugetlb.c | 94 +++++++++++++++++++++++++++++++-------------
mm/hugetlb_vmemmap.c | 36 +++++++++++++++++
mm/hugetlb_vmemmap.h | 10 +++++
3 files changed, 112 insertions(+), 28 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 70fedf8682c4..11de3f885065 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1834,50 +1834,88 @@ 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 *list,
+ struct list_head *non_op_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_op_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_op_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 vmemmap was not restored for ANY folios,
+ * we loop through them trying to restore 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 for one hugetlb page, we free
+ * it and quit processing the list to retry the bulk operation.
+ */
+ list_for_each_entry_safe(folio, t_folio, list, lru)
if (hugetlb_vmemmap_restore(h, &folio->page)) {
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 *list)
+{
+ int ret;
+ LIST_HEAD(non_op_folio);
+ struct folio *folio, *t_folio;
/*
- * 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, list, &non_op_folio);
+ if (ret < 0) {
+ bulk_vmemmap_restore_error(h, list, &non_op_folio);
+ goto retry;
+ }
+
+ /*
+ * At this point, list should be empty, and there should only be
+ * pages on the non_op_folio list. free those entries. Do note
+ * that the non_op_folio list could be empty.
+ */
+ VM_WARN_ON(!list_empty(list));
+ if (!list_empty(&non_op_folio)) {
spin_lock_irq(&hugetlb_lock);
- list_for_each_entry(folio, list, lru)
+ list_for_each_entry(folio, &non_op_folio, 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_op_folio, 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..f827d4efcf8e 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -480,6 +480,42 @@ 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_op_list: Output list of folio for which vmemmap exists.
+ *
+ * Return: %0 if vmemmap exists for all folios on the list and all entries have
+ * been moved to non_op_list. If an error is encountered restoring
+ * vmemmap for ANY folio, an error code will be returned to the
+ * caller. Processing en entries stops when the first error is
+ * encountered. folios processed before the error with vmemmap
+ * will reside on the non_op_list. The folio that experienced the
+ * error and all non-processed folios will remain on folio_list.
+ */
+int hugetlb_vmemmap_restore_folios(const struct hstate *h,
+ struct list_head *folio_list,
+ struct list_head *non_op_list)
non_optimized_list or vmemmap_intact_list? The abbreviation is not
straightforward.
+{
+ struct folio *folio, *t_folio;
+ int ret = 0;
+
+ list_for_each_entry_safe(folio, t_folio, folio_list, lru) {
+ if (folio_test_hugetlb_vmemmap_optimized(folio)) {
hugetlb_vmemmap_restore() has this check as well, so it is unnecessary here.
+ ret = hugetlb_vmemmap_restore(h, &folio->page);
+ if (ret)
+ goto out;
Maybe we could drop the label ("out") and just breaking or returning from
here is enough.
+ }
+
+ /* Add non-optimized folios to output list */
+ list_move(&folio->lru, non_op_list);
+ }
+
+out:
+ 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..e6378ae5c5b6 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);
+int hugetlb_vmemmap_restore_folios(const struct hstate *h,
+ struct list_head *folio_list,
+ struct list_head *non_op_folios);
It is better to keep 3rd name (non_op_folios) consistent with where it is
defined (it is non_op_list).
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 +48,13 @@ static inline int hugetlb_vmemmap_restore(const struct hstate *h, struct page *h
return 0;
}
+static int hugetlb_vmemmap_restore_folios(const struct hstate *h,
+ struct list_head *folio_list,
+ struct list_head *non_op_folios)
+{
+ return 0;
+}
+
static inline void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
{
}