[RFC PATCH 5/8] hugetlb: change free_pool_huge_page to remove_pool_huge_page

Mike Kravetz
2021-03-19T22:44:12Z

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.

Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
---
mm/hugetlb.c | 53 +++++++++++++++++++++++++++++-----------------------
1 file changed, 30 insertions(+), 23 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 3028cf10d504..f60a24e326c2 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1184,7 +1184,7 @@ static int hstate_next_node_to_alloc(struct hstate *h,
}

/*
- * helper for free_pool_huge_page() - return the previously saved
+ * helper for remove_pool_huge_page() - return the previously saved
* node ["this node"] from which to free a huge page. Advance the
* next node id whether or not we find a free huge page to free so
* that the next attempt to free addresses the next node.
@@ -1699,16 +1699,18 @@ static int alloc_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
}

/*
- * Free huge page from pool from next node to free.
- * Attempt to keep persistent huge pages more or less
- * balanced over allowed nodes.
+ * Remove huge page from pool from next node to free. Attempt to keep
+ * persistent huge pages more or less balanced over allowed nodes.
+ * This routine only 'removes' the hugetlb page. The caller must make
+ * an additional call to free the page to low level allocators.
* Called with hugetlb_lock locked.
*/
-static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
- bool acct_surplus)
+static struct page *remove_pool_huge_page(struct hstate *h,
+ nodemask_t *nodes_allowed,
+ bool acct_surplus)
{
int nr_nodes, node;
- int ret = 0;
+ struct page *page = NULL;

for_each_node_mask_to_free(h, nr_nodes, node, nodes_allowed) {
/*
@@ -1717,23 +1719,14 @@ static int free_pool_huge_page(struct hstate *h, nodemask_t *nodes_allowed,
*/
if ((!acct_surplus || h->surplus_huge_pages_node[node]) &&
!list_empty(&h->hugepage_freelists[node])) {
- struct page *page =
- list_entry(h->hugepage_freelists[node].next,
+ page = list_entry(h->hugepage_freelists[node].next,
struct page, lru);
remove_hugetlb_page(h, page, acct_surplus);
- /*
- * unlock/lock around update_and_free_page is temporary
- * and will be removed with subsequent patch.
- */
- spin_unlock(&hugetlb_lock);
- update_and_free_page(h, page);
- spin_lock(&hugetlb_lock);
- ret = 1;
break;
}
}

- return ret;
+ return page;
}

/*
@@ -2064,6 +2057,7 @@ static void return_unused_surplus_pages(struct hstate *h,
unsigned long unused_resv_pages)
{
unsigned long nr_pages;
+ struct page *page;

/* Cannot return gigantic pages currently */
if (hstate_is_gigantic(h))
@@ -2080,7 +2074,7 @@ static void return_unused_surplus_pages(struct hstate *h,
* evenly across all nodes with memory. Iterate across these nodes
* until we can no longer free unreserved surplus pages. This occurs
* when the nodes with surplus pages have no free pages.
- * free_pool_huge_page() will balance the freed pages across the
+ * remove_pool_huge_page() will balance the freed pages across the
* on-line nodes with memory and will handle the hstate accounting.
*
* Note that we decrement resv_huge_pages as we free the pages. If
@@ -2090,9 +2084,15 @@ static void return_unused_surplus_pages(struct hstate *h,
while (nr_pages--) {
h->resv_huge_pages--;
unused_resv_pages--;
- if (!free_pool_huge_page(h, &node_states[N_MEMORY], 1))
+ page = remove_pool_huge_page(h, &node_states[N_MEMORY], 1);
+ if (!page)
goto out;
- cond_resched_lock(&hugetlb_lock);
+
+ /* Drop lock and free page to buddy as it could sleep */
+ spin_unlock(&hugetlb_lock);
+ update_and_free_page(h, page);
+ cond_resched();
+ spin_lock(&hugetlb_lock);
}

out:
@@ -2631,6 +2631,7 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
nodemask_t *nodes_allowed)
{
unsigned long min_count, ret;
+ struct page *page;
NODEMASK_ALLOC(nodemask_t, node_alloc_noretry, GFP_KERNEL);

/*
@@ -2740,9 +2741,15 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
min_count = min_hp_count(h, count);
try_to_free_low(h, count, nodes_allowed);
while (min_count < persistent_huge_pages(h)) {
- if (!free_pool_huge_page(h, nodes_allowed, 0))
+ page = remove_pool_huge_page(h, nodes_allowed, 0);
+ if (!page)
break;
- cond_resched_lock(&hugetlb_lock);
+
+ /* Drop lock as free routines may sleep */
+ spin_unlock(&hugetlb_lock);
+ update_and_free_page(h, page);
+ cond_resched();
+ spin_lock(&hugetlb_lock);

/* Recompute min_count in case hugetlb_lock was dropped */
min_count = min_hp_count(h, count);
--
2.30.2