* [PATCH 1/2] hugetlb: Do not clear hugetlb dtor until allocating vmemmap
[not found] <20230711220942.43706-1-mike.kravetz@oracle.com>
@ 2023-07-11 22:09 ` Mike Kravetz
2023-07-12 8:03 ` Muchun Song
2023-07-11 22:09 ` [PATCH 2/2] hugetlb: optimize update_and_free_pages_bulk to avoid lock cycles Mike Kravetz
1 sibling, 1 reply; 5+ messages in thread
From: Mike Kravetz @ 2023-07-11 22:09 UTC (permalink / raw)
To: linux-mm, linux-kernel
Cc: Jiaqi Yan, Naoya Horiguchi, Muchun Song, Miaohe Lin,
Axel Rasmussen, James Houghton, Michal Hocko, Andrew Morton,
Mike Kravetz, stable
Freeing a hugetlb page and releasing base pages back to the underlying
allocator such as buddy or cma is performed in two steps:
- remove_hugetlb_folio() is called to remove the folio from hugetlb
lists, get a ref on the page and remove hugetlb destructor. This
all must be done under the hugetlb lock. After this call, the page
can be treated as a normal compound page or a collection of base
size pages.
- update_and_free_hugetlb_folio() is called to allocate vmemmap if
needed and the free routine of the underlying allocator is called
on the resulting page. We can not hold the hugetlb lock here.
One issue with this scheme is that a memory error could occur between
these two steps. In this case, the memory error handling code treats
the old hugetlb page as a normal compound page or collection of base
pages. It will then try to SetPageHWPoison(page) on the page with an
error. If the page with error is a tail page without vmemmap, a write
error will occur when trying to set the flag.
Address this issue by modifying remove_hugetlb_folio() and
update_and_free_hugetlb_folio() such that the hugetlb destructor is not
cleared until after allocating vmemmap. Since clearing the destructor
requires holding the hugetlb lock, the clearing is done in
remove_hugetlb_folio() if the vmemmap is present. This saves a
lock/unlock cycle. Otherwise, destructor is cleared in
update_and_free_hugetlb_folio() after allocating vmemmap.
Note that this will leave hugetlb pages in a state where they are marked
free (by hugetlb specific page flag) and have a ref count. This is not
a normal state. The only code that would notice is the memory error
code, and it is set up to retry in such a case.
A subsequent patch will create a routine to do bulk processing of
vmemmap allocation. This will eliminate a lock/unlock cycle for each
hugetlb page in the case where we are freeing a large number of pages.
Fixes: ad2fa3717b74 ("mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page")
Cc: <stable@vger.kernel.org>
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
---
mm/hugetlb.c | 75 +++++++++++++++++++++++++++++++++++-----------------
1 file changed, 51 insertions(+), 24 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index e4a28ce0667f..1b67bf341c32 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1580,9 +1580,37 @@ static inline void destroy_compound_gigantic_folio(struct folio *folio,
unsigned int order) { }
#endif
+static inline void __clear_hugetlb_destructor(struct hstate *h,
+ struct folio *folio)
+{
+ lockdep_assert_held(&hugetlb_lock);
+
+ /*
+ * Very subtle
+ *
+ * For non-gigantic pages set the destructor to the normal compound
+ * page dtor. This is needed in case someone takes an additional
+ * temporary ref to the page, and freeing is delayed until they drop
+ * their reference.
+ *
+ * For gigantic pages set the destructor to the null dtor. This
+ * destructor will never be called. Before freeing the gigantic
+ * page destroy_compound_gigantic_folio will turn the folio into a
+ * simple group of pages. After this the destructor does not
+ * apply.
+ *
+ */
+ if (hstate_is_gigantic(h))
+ folio_set_compound_dtor(folio, NULL_COMPOUND_DTOR);
+ else
+ folio_set_compound_dtor(folio, COMPOUND_PAGE_DTOR);
+}
+
/*
- * Remove hugetlb folio from lists, and update dtor so that the folio appears
- * as just a compound page.
+ * Remove hugetlb folio from lists.
+ * If vmemmap exists for the folio, update dtor so that the folio appears
+ * as just a compound page. Otherwise, wait until after allocating vmemmap
+ * to update dtor.
*
* A reference is held on the folio, except in the case of demote.
*
@@ -1613,31 +1641,19 @@ static void __remove_hugetlb_folio(struct hstate *h, struct folio *folio,
}
/*
- * Very subtle
- *
- * For non-gigantic pages set the destructor to the normal compound
- * page dtor. This is needed in case someone takes an additional
- * temporary ref to the page, and freeing is delayed until they drop
- * their reference.
- *
- * For gigantic pages set the destructor to the null dtor. This
- * destructor will never be called. Before freeing the gigantic
- * page destroy_compound_gigantic_folio will turn the folio into a
- * simple group of pages. After this the destructor does not
- * apply.
- *
- * This handles the case where more than one ref is held when and
- * after update_and_free_hugetlb_folio is called.
- *
- * In the case of demote we do not ref count the page as it will soon
- * be turned into a page of smaller size.
+ * We can only clear the hugetlb destructor after allocating vmemmap
+ * pages. Otherwise, someone (memory error handling) may try to write
+ * to tail struct pages.
+ */
+ if (!folio_test_hugetlb_vmemmap_optimized(folio))
+ __clear_hugetlb_destructor(h, folio);
+
+ /*
+ * In the case of demote we do not ref count the page as it will soon
+ * be turned into a page of smaller size.
*/
if (!demote)
folio_ref_unfreeze(folio, 1);
- if (hstate_is_gigantic(h))
- folio_set_compound_dtor(folio, NULL_COMPOUND_DTOR);
- else
- folio_set_compound_dtor(folio, COMPOUND_PAGE_DTOR);
h->nr_huge_pages--;
h->nr_huge_pages_node[nid]--;
@@ -1706,6 +1722,7 @@ static void __update_and_free_hugetlb_folio(struct hstate *h,
{
int i;
struct page *subpage;
+ bool clear_dtor = folio_test_hugetlb_vmemmap_optimized(folio);
if (hstate_is_gigantic(h) && !gigantic_page_runtime_supported())
return;
@@ -1736,6 +1753,16 @@ static void __update_and_free_hugetlb_folio(struct hstate *h,
if (unlikely(folio_test_hwpoison(folio)))
folio_clear_hugetlb_hwpoison(folio);
+ /*
+ * If vmemmap pages were allocated above, then we need to clear the
+ * hugetlb destructor under the hugetlb lock.
+ */
+ if (clear_dtor) {
+ spin_lock_irq(&hugetlb_lock);
+ __clear_hugetlb_destructor(h, folio);
+ spin_unlock_irq(&hugetlb_lock);
+ }
+
for (i = 0; i < pages_per_huge_page(h); i++) {
subpage = folio_page(folio, i);
subpage->flags &= ~(1 << PG_locked | 1 << PG_error |
--
2.41.0
^ permalink raw reply related [flat|nested] 5+ messages in thread* [PATCH 2/2] hugetlb: optimize update_and_free_pages_bulk to avoid lock cycles
[not found] <20230711220942.43706-1-mike.kravetz@oracle.com>
2023-07-11 22:09 ` [PATCH 1/2] hugetlb: Do not clear hugetlb dtor until allocating vmemmap Mike Kravetz
@ 2023-07-11 22:09 ` Mike Kravetz
1 sibling, 0 replies; 5+ messages in thread
From: Mike Kravetz @ 2023-07-11 22:09 UTC (permalink / raw)
To: linux-mm, linux-kernel
Cc: Jiaqi Yan, Naoya Horiguchi, Muchun Song, Miaohe Lin,
Axel Rasmussen, James Houghton, Michal Hocko, Andrew Morton,
Mike Kravetz, stable
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
Fixes: ad2fa3717b74 ("mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page")
Cc: <stable@vger.kernel.org>
Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
---
mm/hugetlb.c | 35 ++++++++++++++++++++++++++++++++++-
1 file changed, 34 insertions(+), 1 deletion(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 1b67bf341c32..e751fced870a 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1856,11 +1856,44 @@ static void update_and_free_pages_bulk(struct hstate *h, struct list_head *list)
{
struct page *page, *t_page;
struct folio *folio;
+ bool clear_dtor = false;
+ /*
+ * First allocate required vmemmmap for all pages on list. If vmemmap
+ * can not be allocated, we can not free page to lower level allocator,
+ * so add back as hugetlb surplus page.
+ */
+ list_for_each_entry_safe(page, t_page, list, lru) {
+ if (HPageVmemmapOptimized(page)) {
+ clear_dtor = true;
+ if (hugetlb_vmemmap_restore(h, page)) {
+ spin_lock_irq(&hugetlb_lock);
+ add_hugetlb_folio(h, folio, true);
+ spin_unlock_irq(&hugetlb_lock);
+ }
+ cond_resched();
+ }
+ }
+
+ /*
+ * If vmemmmap allocation performed above, then take lock * to clear
+ * destructor of all pages on list.
+ */
+ if (clear_dtor) {
+ spin_lock_irq(&hugetlb_lock);
+ list_for_each_entry(page, list, lru)
+ __clear_hugetlb_destructor(h, page_folio(page));
+ spin_unlock_irq(&hugetlb_lock);
+ }
+
+ /*
+ * Free pages 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(page, t_page, list, lru) {
folio = page_folio(page);
update_and_free_hugetlb_folio(h, folio, false);
- cond_resched();
}
}
--
2.41.0
^ permalink raw reply related [flat|nested] 5+ messages in thread