On 3/25/21 3:55 AM, Michal Hocko wrote:
> On Wed 24-03-21 17:28:32, Mike Kravetz wrote:
>> With the introduction of remove_hugetlb_page(), there is no need for
>> update_and_free_page to hold the hugetlb lock. Change all callers to
>> drop the lock before calling.
>>
>> With additional code modifications, this will allow loops which decrease
>> the huge page pool to drop the hugetlb_lock with each page to reduce
>> long hold times.
>>
>> The ugly unlock/lock cycle in free_pool_huge_page will be removed in
>> a subsequent patch which restructures free_pool_huge_page.
>>
>> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
>
> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
>
> One minor thing below
>
> [...]
>> @@ -2563,22 +2572,37 @@ static void try_to_free_low(struct hstate *h, unsigned long count,
>> nodemask_t *nodes_allowed)
>> {
>> int i;
>> + struct list_head page_list;
>> + struct page *page, *next;
>>
>> if (hstate_is_gigantic(h))
>> return;
>>
>> + /*
>> + * Collect pages to be freed on a list, and free after dropping lock
>> + */
>> + INIT_LIST_HEAD(&page_list);
>> for_each_node_mask(i, *nodes_allowed) {
>> - struct page *page, *next;
>> struct list_head *freel = &h->hugepage_freelists[i];
>> list_for_each_entry_safe(page, next, freel, lru) {
>> if (count >= h->nr_huge_pages)
>> - return;
>> + goto out;
>> if (PageHighMem(page))
>> continue;
>> remove_hugetlb_page(h, page, false);
>> - update_and_free_page(h, page);
>> + INIT_LIST_HEAD(&page->lru);
>
> What is the point of rhis INIT_LIST_HEAD? Page has been removed from the
> list by remove_hugetlb_page so it can be added to a new one without any
> reinitialization.
remove_hugetlb_page just does a list_del. list_del will poison the
pointers in page->lru. The following list_add will then complain about
list corruption.
I could replace the list_del in remove_hugetlb_page with list_del_init.
However, not all callers of remove_hugetlb_page will be adding the page
to a list. If we just call update_and_free_page, there is no need to
reinitialize the list pointers.
Might be better to just use list_del_init in remove_hugetlb_page to
avoid any questions like this.
--
Mike Kravetz
>
>> + list_add(&page->lru, &page_list);
>> }
>> }
>> +
>> +out:
>> + spin_unlock(&hugetlb_lock);
>> + list_for_each_entry_safe(page, next, &page_list, lru) {
>> + list_del(&page->lru);
>> + update_and_free_page(h, page);
>> + cond_resched();
>> + }
>> + spin_lock(&hugetlb_lock);
>> }
>> #else
>> static inline void try_to_free_low(struct hstate *h, unsigned long count,
>> --
>> 2.30.2
>>
>
