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SubjectRe: [PATCH v4 4/8] hugetlb: perform vmemmap restoration on a list of pages
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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@linux.dev> wrote:
>>>>>> On Sep 20, 2023, at 04:57, Mike Kravetz <mike.kravetz@oracle.com> 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@oracle.com>
> 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@oracle.com>
> ---
> 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)
> {
> }

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