On Mon, Apr 05, 2021 at 04:00:40PM -0700, 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 <[email protected]>
Without looking too close at the changes made to alloc_and_dissolve_huge_page(): Reviewed-by: Oscar Salvador <[email protected]> One question below: > @@ -2671,22 +2682,34 @@ static void try_to_free_low(struct hstate *h, > unsigned long count, > nodemask_t *nodes_allowed) > { > int i; > + struct page *page, *next; > + LIST_HEAD(page_list); > > if (hstate_is_gigantic(h)) > return; > > + /* > + * Collect pages to be freed on a list, and free after dropping lock > + */ > 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); > + list_add(&page->lru, &page_list); > } > } > + > +out: > + spin_unlock(&hugetlb_lock); > + list_for_each_entry_safe(page, next, &page_list, lru) { > + update_and_free_page(h, page); > + cond_resched(); > + } > + spin_lock(&hugetlb_lock); Can we get here with an empty list? Maybe if someone raced with us manipulating nr_huge_pages? AFAICS, this gets called under the lock, and the adjusting in remove_hugetlb_page() gets also done under the lock, so I guess this is not possible to happen. The reason I am asking is whether we want to check for the list to be empty before we do the unacquire/acquire lock dancing. -- Oscar Salvador SUSE L3
