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Subject[RFC PATCH v1 11/13] mm: use lru_batch locking in release_pages
Date
Introduce LRU batch locking in release_pages.  This is the code path
where I see lru_lock contention most often, so this is the one I used in
this prototype.

Signed-off-by: Daniel Jordan <daniel.m.jordan@oracle.com>
---
mm/swap.c | 45 +++++++++++++++++----------------------------
1 file changed, 17 insertions(+), 28 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index 2bb28fcb7cc0..fae766e035a4 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -745,31 +745,21 @@ void release_pages(struct page **pages, int nr)
int i;
LIST_HEAD(pages_to_free);
struct pglist_data *locked_pgdat = NULL;
+ spinlock_t *locked_lru_batch = NULL;
struct lruvec *lruvec;
unsigned long uninitialized_var(flags);
- unsigned int uninitialized_var(lock_batch);

for (i = 0; i < nr; i++) {
struct page *page = pages[i];

- /*
- * Make sure the IRQ-safe lock-holding time does not get
- * excessive with a continuous string of pages from the
- * same pgdat. The lock is held only if pgdat != NULL.
- */
- if (locked_pgdat && ++lock_batch == SWAP_CLUSTER_MAX) {
- lru_unlock_all(locked_pgdat, &flags);
- locked_pgdat = NULL;
- }
-
if (is_huge_zero_page(page))
continue;

/* Device public page can not be huge page */
if (is_device_public_page(page)) {
- if (locked_pgdat) {
- lru_unlock_all(locked_pgdat, &flags);
- locked_pgdat = NULL;
+ if (locked_lru_batch) {
+ lru_batch_unlock(NULL, &locked_lru_batch,
+ &locked_pgdat, &flags);
}
put_zone_device_private_or_public_page(page);
continue;
@@ -780,26 +770,23 @@ void release_pages(struct page **pages, int nr)
continue;

if (PageCompound(page)) {
- if (locked_pgdat) {
- lru_unlock_all(locked_pgdat, &flags);
- locked_pgdat = NULL;
+ if (locked_lru_batch) {
+ lru_batch_unlock(NULL, &locked_lru_batch,
+ &locked_pgdat, &flags);
}
__put_compound_page(page);
continue;
}

if (PageLRU(page)) {
- struct pglist_data *pgdat = page_pgdat(page);
-
- if (pgdat != locked_pgdat) {
- if (locked_pgdat)
- lru_unlock_all(locked_pgdat, &flags);
- lock_batch = 0;
- locked_pgdat = pgdat;
- lru_lock_all(locked_pgdat, &flags);
+ if (locked_lru_batch) {
+ lru_batch_unlock(page, &locked_lru_batch,
+ &locked_pgdat, &flags);
}
+ lru_batch_lock(page, &locked_lru_batch, &locked_pgdat,
+ &flags);

- lruvec = mem_cgroup_page_lruvec(page, locked_pgdat);
+ lruvec = mem_cgroup_page_lruvec(page, page_pgdat(page));
VM_BUG_ON_PAGE(!PageLRU(page), page);
__ClearPageLRU(page);
del_page_from_lru_list(page, lruvec, page_off_lru(page));
@@ -811,8 +798,10 @@ void release_pages(struct page **pages, int nr)

list_add(&page->lru, &pages_to_free);
}
- if (locked_pgdat)
- lru_unlock_all(locked_pgdat, &flags);
+ if (locked_lru_batch) {
+ lru_batch_unlock(NULL, &locked_lru_batch, &locked_pgdat,
+ &flags);
+ }

mem_cgroup_uncharge_list(&pages_to_free);
free_unref_page_list(&pages_to_free);
--
2.16.1
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