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 <[email protected]>
---
mm/hugetlb.c | 98 +++++++++++++++++++++++++++++++-------------
mm/hugetlb_vmemmap.c | 38 +++++++++++++++++
mm/hugetlb_vmemmap.h | 10 +++++
3 files changed, 118 insertions(+), 28 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index da0ebd370b5f..53df35fbc3f2 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1834,50 +1834,92 @@ 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)) {
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..0b7710f90e38 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 +48,13 @@ 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)
+{
+ return 0;
+}
+
static inline void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
{
}
--
2.41.0
On 2023/9/25 08:39, Mike Kravetz wrote:
> 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 <[email protected]>
> ---
> mm/hugetlb.c | 98 +++++++++++++++++++++++++++++++-------------
> mm/hugetlb_vmemmap.c | 38 +++++++++++++++++
> mm/hugetlb_vmemmap.h | 10 +++++
> 3 files changed, 118 insertions(+), 28 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index da0ebd370b5f..53df35fbc3f2 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1834,50 +1834,92 @@ 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)) {
IIUC, the folio should be deleted from the folio list since this
huge page will be added to the free list (the list is corrupted),
right?
> 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..0b7710f90e38 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 +48,13 @@ 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)
> +{
> + return 0;
> +}
> +
> static inline void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head)
> {
> }
On 09/25/23 21:54, Muchun Song wrote:
>
>
> On 2023/9/25 08:39, Mike Kravetz wrote:
> > 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 <[email protected]>
> > ---
> > mm/hugetlb.c | 98 +++++++++++++++++++++++++++++++-------------
> > mm/hugetlb_vmemmap.c | 38 +++++++++++++++++
> > mm/hugetlb_vmemmap.h | 10 +++++
> > 3 files changed, 118 insertions(+), 28 deletions(-)
> >
> > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > index da0ebd370b5f..53df35fbc3f2 100644
> > --- a/mm/hugetlb.c
> > +++ b/mm/hugetlb.c
> > @@ -1834,50 +1834,92 @@ 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)) {
>
> IIUC, the folio should be deleted from the folio list since this
> huge page will be added to the free list (the list is corrupted),
> right?
Good catch! Yes, we should remove from the list here.
I did exercise this specific code path and there was no list corruption. In
any case, I will add the list_del().
Thank you!
--
Mike Kravetz
On 09/25/23 10:12, Mike Kravetz wrote:
> On 09/25/23 21:54, Muchun Song wrote:
> >
> >
> > On 2023/9/25 08:39, Mike Kravetz wrote:
> > > 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 <[email protected]>
> > > ---
> > > mm/hugetlb.c | 98 +++++++++++++++++++++++++++++++-------------
> > > mm/hugetlb_vmemmap.c | 38 +++++++++++++++++
> > > mm/hugetlb_vmemmap.h | 10 +++++
> > > 3 files changed, 118 insertions(+), 28 deletions(-)
> > >
> > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> > > index da0ebd370b5f..53df35fbc3f2 100644
> > > --- a/mm/hugetlb.c
> > > +++ b/mm/hugetlb.c
> > > @@ -1834,50 +1834,92 @@ 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)) {
> >
> > IIUC, the folio should be deleted from the folio list since this
> > huge page will be added to the free list (the list is corrupted),
> > right?
>
> Good catch! Yes, we should remove from the list here.
>
> I did exercise this specific code path and there was no list corruption. In
> any case, I will add the list_del().
Correction. My testing with simulated errors took the else branch here.
--
Mike Kravetz