[PATCH v1 5/8] mm: zswap: Store the folio's node id in the zswap_entry.

[Kanchana P. Sridhar]

When storing a folio in zswap, save the folio's node id in the zswap
entry instead of relying on the zswap_entry being allocated on the same
node. This enables optimizations such as batch allocation of zswap
entries for large folios using kmem_cache_alloc_bulk() that does not
support specifying a node id.

The size of the zswap_entry remains unchanged as 'referenced' is lumped
in with the 'length' (as it doesn't need a full unsigned int anyway).

Suggested-by: Nhat Pham <nphamcs@xxxxxxxxx>
Suggested-by: Yosry Ahmed <yosry.ahmed@xxxxxxxxx>
Signed-off-by: Kanchana P Sridhar <kanchana.p.sridhar@xxxxxxxxx>
Signed-off-by: Kanchana P. Sridhar <kanchanapsridhar2026@xxxxxxxxx>
---
 mm/zswap.c | 23 +++++++++++------------
 1 file changed, 11 insertions(+), 12 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index ca513a9f89e3..c2731d3acb2c 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -194,6 +194,7 @@ static struct shrinker *zswap_shrinker;
  *              writeback logic. The entry is only reclaimed by the writeback
  *              logic if referenced is unset. See comments in the shrinker
  *              section for context.
+ * nid - NUMA node id of the page for which this is the zswap entry.
  * pool_idx - id of the zswap_pool that the entry's data is in.
  * handle - zsmalloc allocation handle that stores the compressed page data
  * objcg - the obj_cgroup that the compressed memory is charged to
@@ -201,8 +202,11 @@ static struct shrinker *zswap_shrinker;
  */
 struct zswap_entry {
 	swp_entry_t swpentry;
-	unsigned int length;
-	bool referenced;
+	struct {
+		unsigned int length:31;
+		bool referenced:1;
+	};
+	int nid;
 	u8 pool_idx;
 	unsigned long handle;
 	struct obj_cgroup *objcg;
@@ -672,14 +676,8 @@ static int zswap_enabled_param_set(const char *val,
 * lru functions
 **********************************/
 
-static inline int entry_to_nid(struct zswap_entry *entry)
-{
-	return page_to_nid(virt_to_page(entry));
-}
-
 static void zswap_lru_add(struct zswap_entry *entry)
 {
-	int nid = entry_to_nid(entry);
 	struct mem_cgroup *memcg;
 
 	/*
@@ -696,19 +694,18 @@ static void zswap_lru_add(struct zswap_entry *entry)
 	rcu_read_lock();
 	memcg = obj_cgroup_memcg(entry->objcg);
 	/* will always succeed */
-	list_lru_add(&zswap_list_lru, &entry->lru, nid, memcg);
+	list_lru_add(&zswap_list_lru, &entry->lru, entry->nid, memcg);
 	rcu_read_unlock();
 }
 
 static void zswap_lru_del(struct zswap_entry *entry)
 {
-	int nid = entry_to_nid(entry);
 	struct mem_cgroup *memcg;
 
 	rcu_read_lock();
 	memcg = obj_cgroup_memcg(entry->objcg);
 	/* will always succeed */
-	list_lru_del(&zswap_list_lru, &entry->lru, nid, memcg);
+	list_lru_del(&zswap_list_lru, &entry->lru, entry->nid, memcg);
 	rcu_read_unlock();
 }
 
@@ -1449,9 +1446,10 @@ static bool zswap_store_page(struct folio *folio, long index,
 {
 	swp_entry_t page_swpentry = folio_swap_entry(folio, index);
 	struct zswap_entry *entry, *old;
+	int nid = folio_nid(folio);
 
 	/* allocate entry */
-	entry = zswap_entry_cache_alloc(GFP_KERNEL, folio_nid(folio));
+	entry = zswap_entry_cache_alloc(GFP_KERNEL, nid);
 	if (!entry) {
 		zswap_reject_kmemcache_fail++;
 		return false;
@@ -1466,6 +1464,7 @@ static bool zswap_store_page(struct folio *folio, long index,
 	 * to an unrelated live pool.
 	 */
 	entry->pool_idx = pool->idx;
+	entry->nid = nid;
 
 	old = xa_store(swap_zswap_tree(page_swpentry),
 		       swp_offset(page_swpentry),
-- 
2.39.5