[PATCH 2/6] mm/zswap: invalidate zswap entry when swap entry free

Chengming Zhou
2024-02-01T15:50:24Z

During testing I found there are some times the zswap_writeback_entry()
return -ENOMEM, which is not we expected:

bpftrace -e 'kr:zswap_writeback_entry {@[(int32)retval]=count()}'
@[-12]: 1563
@[0]: 277221

The reason is that __read_swap_cache_async() return NULL because
swapcache_prepare() failed. The reason is that we won't invalidate
zswap entry when swap entry freed to the per-cpu pool, these zswap
entries are still on the zswap tree and lru list.

This patch moves the invalidation ahead to when swap entry freed
to the per-cpu pool, since there is no any benefit to leave trashy
zswap entry on the tree and lru list.

With this patch:
bpftrace -e 'kr:zswap_writeback_entry {@[(int32)retval]=count()}'
@[0]: 259744

Note: large folio can't have zswap entry for now, so don't bother
to add zswap entry invalidation in the large folio swap free path.

Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com>
---
include/linux/zswap.h | 4 ++--
mm/swap_slots.c | 2 ++
mm/swapfile.c | 1 -
mm/zswap.c | 5 +++--
4 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/linux/zswap.h b/include/linux/zswap.h
index 91895ce1fdbc..341aea490070 100644
--- a/include/linux/zswap.h
+++ b/include/linux/zswap.h
@@ -29,7 +29,7 @@ struct zswap_lruvec_state {

bool zswap_store(struct folio *folio);
bool zswap_load(struct folio *folio);
-void zswap_invalidate(int type, pgoff_t offset);
+void zswap_invalidate(swp_entry_t swp);
int zswap_swapon(int type, unsigned long nr_pages);
void zswap_swapoff(int type);
void zswap_memcg_offline_cleanup(struct mem_cgroup *memcg);
@@ -50,7 +50,7 @@ static inline bool zswap_load(struct folio *folio)
return false;
}

-static inline void zswap_invalidate(int type, pgoff_t offset) {}
+static inline void zswap_invalidate(swp_entry_t swp) {}
static inline int zswap_swapon(int type, unsigned long nr_pages)
{
return 0;
diff --git a/mm/swap_slots.c b/mm/swap_slots.c
index 0bec1f705f8e..d24cdea26daa 100644
--- a/mm/swap_slots.c
+++ b/mm/swap_slots.c
@@ -273,6 +273,8 @@ void free_swap_slot(swp_entry_t entry)
{
struct swap_slots_cache *cache;

+ zswap_invalidate(entry);
+
cache = raw_cpu_ptr(&swp_slots);
if (likely(use_swap_slot_cache && cache->slots_ret)) {
spin_lock_irq(&cache->free_lock);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 0580bb3e34d7..65b49db89b36 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -744,7 +744,6 @@ static void swap_range_free(struct swap_info_struct *si, unsigned long offset,
swap_slot_free_notify = NULL;
while (offset <= end) {
arch_swap_invalidate_page(si->type, offset);
- zswap_invalidate(si->type, offset);
if (swap_slot_free_notify)
swap_slot_free_notify(si->bdev, offset);
offset++;
diff --git a/mm/zswap.c b/mm/zswap.c
index 735f1a6ef336..d8bb0e06e2b0 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1738,9 +1738,10 @@ bool zswap_load(struct folio *folio)
return true;
}

-void zswap_invalidate(int type, pgoff_t offset)
+void zswap_invalidate(swp_entry_t swp)
{
- struct zswap_tree *tree = swap_zswap_tree(swp_entry(type, offset));
+ pgoff_t offset = swp_offset(swp);
+ struct zswap_tree *tree = swap_zswap_tree(swp);
struct zswap_entry *entry;

spin_lock(&tree->lock);

--
b4 0.10.1