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.
Signed-off-by: Mike Kravetz <[email protected]>
Reviewed-by: Muchun Song <[email protected]>
Acked-by: Michal Hocko <[email protected]>
---
mm/hugetlb.c | 93 ++++++++++++++++++++++++++++------------------------
1 file changed, 51 insertions(+), 42 deletions(-)
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index be6031a8e2a9..93a2a11b9376 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -1204,7 +1204,7 @@ 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.
@@ -1386,6 +1386,16 @@ static void update_and_free_page(struct hstate *h, struct page *page)
}
}
+static void update_and_free_pages_bulk(struct hstate *h, struct list_head *list)
+{
+ struct page *page, *t_page;
+
+ list_for_each_entry_safe(page, t_page, list, lru) {
+ update_and_free_page(h, page);
+ cond_resched();
+ }
+}
+
struct hstate *size_to_hstate(unsigned long size)
{
struct hstate *h;
@@ -1716,16 +1726,18 @@ 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) {
/*
@@ -1734,23 +1746,14 @@ 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;
}
/*
@@ -2070,17 +2073,16 @@ static int gather_surplus_pages(struct hstate *h, long delta)
* to the associated reservation map.
* 2) Free any unused surplus pages that may have been allocated to satisfy
* the reservation. As many as unused_resv_pages may be freed.
- *
- * Called with hugetlb_lock held. However, the lock could be dropped (and
- * reacquired) during calls to cond_resched_lock. Whenever dropping the lock,
- * we must make sure nobody else can claim pages we are in the process of
- * freeing. Do this by ensuring resv_huge_page always is greater than the
- * number of huge pages we plan to free when dropping the lock.
*/
static void return_unused_surplus_pages(struct hstate *h,
unsigned long unused_resv_pages)
{
unsigned long nr_pages;
+ struct page *page;
+ LIST_HEAD(page_list);
+
+ /* Uncommit the reservation */
+ h->resv_huge_pages -= unused_resv_pages;
/* Cannot return gigantic pages currently */
if (hstate_is_gigantic(h))
@@ -2097,24 +2099,21 @@ 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
- * we drop the lock, resv_huge_pages will still be sufficiently large
- * to cover subsequent pages we may free.
*/
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);
+
+ list_add(&page->lru, &page_list);
}
out:
- /* Fully uncommit the reservation */
- h->resv_huge_pages -= unused_resv_pages;
+ spin_unlock(&hugetlb_lock);
+ update_and_free_pages_bulk(h, &page_list);
+ spin_lock(&hugetlb_lock);
}
@@ -2682,7 +2681,6 @@ 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))
@@ -2692,6 +2690,7 @@ static void try_to_free_low(struct hstate *h, unsigned long count,
* 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)
@@ -2705,10 +2704,7 @@ static void try_to_free_low(struct hstate *h, unsigned long count,
out:
spin_unlock(&hugetlb_lock);
- list_for_each_entry_safe(page, next, &page_list, lru) {
- update_and_free_page(h, page);
- cond_resched();
- }
+ update_and_free_pages_bulk(h, &page_list);
spin_lock(&hugetlb_lock);
}
#else
@@ -2755,6 +2751,8 @@ 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;
+ LIST_HEAD(page_list);
NODEMASK_ALLOC(nodemask_t, node_alloc_noretry, GFP_KERNEL);
/*
@@ -2867,11 +2865,22 @@ static int set_max_huge_pages(struct hstate *h, unsigned long count, int nid,
min_count = h->resv_huge_pages + h->nr_huge_pages - h->free_huge_pages;
min_count = max(count, min_count);
try_to_free_low(h, min_count, nodes_allowed);
+
+ /*
+ * Collect pages to be removed on list without dropping lock
+ */
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);
+
+ list_add(&page->lru, &page_list);
}
+ /* free the pages after dropping lock */
+ spin_unlock(&hugetlb_lock);
+ update_and_free_pages_bulk(h, &page_list);
+ spin_lock(&hugetlb_lock);
+
while (count < persistent_huge_pages(h)) {
if (!adjust_pool_surplus(h, nodes_allowed, 1))
break;
--
2.30.2
On Mon, Apr 05, 2021 at 04:00:41PM -0700, Mike Kravetz wrote:
> 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.
>
> 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]>
It crossed my mind that we could use update_and_free_pages_bulk() from
dissolve_free_huge_pages() <-> dissolve_free_huge_page() but the latter
looks too hairy already and it is probably not worth it.
--
Oscar Salvador
SUSE L3