> 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:
>>> 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.
>>>
>>> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
>>> ---
>>> mm/hugetlb.c | 36 ++++++++++++++++++------------------
>>> mm/hugetlb_vmemmap.c | 37 +++++++++++++++++++++++++++++++++++++
>>> mm/hugetlb_vmemmap.h | 11 +++++++++++
>>> 3 files changed, 66 insertions(+), 18 deletions(-)
>>>
>>> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
>>> index d6f3db3c1313..814bb1982274 100644
>>> --- a/mm/hugetlb.c
>>> +++ b/mm/hugetlb.c
>>> @@ -1836,36 +1836,36 @@ static void update_and_free_hugetlb_folio(struct hstate *h, struct folio *folio,
>>> static void update_and_free_pages_bulk(struct hstate *h, struct list_head *list)
>>> {
>>> + int ret;
>>> + unsigned long restored;
>>> 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.
>>> + * First allocate required vmemmmap (if necessary) for all folios.
>>> */
>>> - list_for_each_entry_safe(folio, t_folio, list, lru) {
>>> - if (folio_test_hugetlb_vmemmap_optimized(folio)) {
>>> - if (hugetlb_vmemmap_restore(h, &folio->page)) {
>>> - spin_lock_irq(&hugetlb_lock);
>>> + ret = hugetlb_vmemmap_restore_folios(h, list, &restored);
>>> +
>>> + /*
>>> + * If there was an error restoring vmemmap for ANY folios on the list,
>>> + * add them back as surplus hugetlb pages. add_hugetlb_folio() removes
>>> + * the folio from THIS list.
>>> + */
>>> + if (ret < 0) {
>>> + spin_lock_irq(&hugetlb_lock);
>>> + list_for_each_entry_safe(folio, t_folio, list, lru)
>>> + if (folio_test_hugetlb_vmemmap_optimized(folio))
>>> add_hugetlb_folio(h, folio, true);
>>> - spin_unlock_irq(&hugetlb_lock);
>>> - } else
>>> - clear_dtor = true;
>>> - }
>>> + spin_unlock_irq(&hugetlb_lock);
>>> }
>>> /*
>>> - * If vmemmmap allocation was performed on any folio above, take lock
>>> - * to clear destructor of all folios on list. This avoids the need to
>>> + * If vmemmmap allocation was performed on ANY folio , 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.
>>> */
>>> - if (clear_dtor) {
>>> + if (restored) {
>>> spin_lock_irq(&hugetlb_lock);
>>> list_for_each_entry(folio, list, lru)
>>> __clear_hugetlb_destructor(h, folio);
>>> diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
>>> index 4558b814ffab..463a4037ec6e 100644
>>> --- a/mm/hugetlb_vmemmap.c
>>> +++ b/mm/hugetlb_vmemmap.c
>>> @@ -480,6 +480,43 @@ 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: 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.
>>> + */
>>> +int hugetlb_vmemmap_restore_folios(const struct hstate *h,
>>> + struct list_head *folio_list,
>>> + unsigned long *restored)
>>> +{
>>> + unsigned long num_restored;
>>> + struct folio *folio;
>>> + int ret = 0, t_ret;
>>> +
>>> + num_restored = 0;
>>> + list_for_each_entry(folio, folio_list, lru) {
>>> + if (folio_test_hugetlb_vmemmap_optimized(folio)) {
>>> + t_ret = hugetlb_vmemmap_restore(h, &folio->page);
>>
>> I still think we should free a non-optimized HugeTLB page if we
>> encounter an OOM situation instead of continue to restore
>> vemmmap pages. Restoring vmemmmap pages will only aggravate
>> the OOM situation. The suitable appraoch is to free a non-optimized
>> HugeTLB page to satisfy our allocation of vmemmap pages, what's
>> your opinion, Mike?
>
> I agree.
>
> As you mentioned previously, this may complicate this code path a bit.
> I will rewrite to make this happen.
Maybe we could introduced two list passed to update_and_free_pages_bulk (this
will be easy for the callers of it), one is for non-optimized huge page,
another is optimized one. In update_and_free_pages_bulk, we could first
free those non-optimized huge page, and then restore vemmmap pages for
those optimized ones, in which case, the code could be simple.
hugetlb_vmemmap_restore_folios() dose not need to add complexity, which
still continue to restore vmemmap pages and will stop once we encounter
an OOM situation.
Thanks.
> --
> Mike Kravetz
