hugetlb: change free_pool_huge_page to remove_pool_huge_page

free_pool_huge_page was called with hugetlb_lock held.  It would remove
a hugetlb page, and then free the corresponding pages to the lower level
allocators such as buddy.  free_pool_huge_page was called in a loop to
remove hugetlb pages and these loops could hold the hugetlb_lock for a
considerable time.

Create new routine remove_pool_huge_page to replace free_pool_huge_page.
remove_pool_huge_page will remove the hugetlb page, and it must be
called with the hugetlb_lock held.  It will return the removed page and
it is the responsibility of the caller to free the page to the lower
level allocators.  The hugetlb_lock is dropped before freeing to these
allocators which results in shorter lock hold times.

Add new helper routine to call update_and_free_page for a list of pages.

Note: Some changes to the routine return_unused_surplus_pages are in
need of explanation.  Commit e5bbc8a6c992 ("mm/hugetlb.c: fix
reservation race when freeing surplus pages") modified this routine to
address a race which could occur when dropping the hugetlb_lock in the
loop that removes pool pages.  Accounting changes introduced in that
commit were subtle and took some thought to understand.  This commit
removes the cond_resched_lock() and the potential race.  Therefore,
remove the subtle code and restore the more straight forward accounting
effectively reverting the commit.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Mike Kravetz <[email protected]>
Reviewed-by: Muchun Song <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Reviewed-by: Oscar Salvador <[email protected]>
Cc: "Aneesh Kumar K . V" <[email protected]>
Cc: Barry Song <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Hillf Danton <[email protected]>
Cc: HORIGUCHI NAOYA <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Miaohe Lin <[email protected]>
Cc: Mina Almasry <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Roman Gushchin <[email protected]>
Cc: Shakeel Butt <[email protected]>
Cc: Waiman Long <[email protected]>
Cc: Will Deacon <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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