The patch titled
Subject: hugetlb: optimize update_and_free_pages_bulk to avoid lock cycles
has been added to the -mm mm-unstable branch. Its filename is
hugetlb-optimize-update_and_free_pages_bulk-to-avoid-lock-cycles.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/hugetlb-optimize-update_and_free_pages_bulk-to-avoid-lock-cycles.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Subject: hugetlb: optimize update_and_free_pages_bulk to avoid lock cycles
Date: Fri, 15 Sep 2023 15:15:38 -0700
update_and_free_pages_bulk is designed to free a list of hugetlb pages
back to their associated lower level allocators. This may require
allocating vmemmmap pages associated with each hugetlb page. The
hugetlb page destructor must be changed before pages are freed to lower
level allocators. However, the destructor must be changed under the
hugetlb lock. This means there is potentially one lock cycle per page.
Minimize the number of lock cycles in update_and_free_pages_bulk by:
1) allocating necessary vmemmap for all hugetlb pages on the list
2) take hugetlb lock and clear destructor for all pages on the list
3) free all pages on list back to low level allocators
Link: https://lkml.kernel.org/r/20230915221548.552084-6-mike.kravetz@xxxxxxxxxx
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Acked-by: James Houghton <jthoughton@xxxxxxxxxx>
Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Joao Martins <joao.m.martins@xxxxxxxxxx>
Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Naoya Horiguchi <naoya.horiguchi@xxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Sidhartha Kumar <sidhartha.kumar@xxxxxxxxxx>
Cc: Xiongchun Duan <duanxiongchun@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/hugetlb.c | 39 +++++++++++++++++++++++++++++++++++++++
1 file changed, 39 insertions(+)
--- a/mm/hugetlb.c~hugetlb-optimize-update_and_free_pages_bulk-to-avoid-lock-cycles
+++ a/mm/hugetlb.c
@@ -1830,7 +1830,46 @@ static void update_and_free_hugetlb_foli
static void update_and_free_pages_bulk(struct hstate *h, struct list_head *list)
{
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 (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;
+ }
+ }
+
+ /*
+ * 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.
+ */
+ if (clear_dtor) {
+ spin_lock_irq(&hugetlb_lock);
+ list_for_each_entry(folio, list, 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) {
update_and_free_hugetlb_folio(h, folio, false);
cond_resched();
_
Patches currently in -mm which might be from mike.kravetz@xxxxxxxxxx are
hugetlb-set-hugetlb-page-flag-before-optimizing-vmemmap.patch
hugetlb-optimize-update_and_free_pages_bulk-to-avoid-lock-cycles.patch
hugetlb-restructure-pool-allocations.patch
hugetlb-perform-vmemmap-optimization-on-a-list-of-pages.patch
hugetlb-perform-vmemmap-restoration-on-a-list-of-pages.patch
hugetlb-batch-freeing-of-vmemmap-pages.patch
hugetlb-batch-tlb-flushes-when-restoring-vmemmap.patch
