zsmalloc: prefer the the original page's node for compressed data

Currently, zsmalloc, zswap's and zram's backend memory allocator, does not
enforce any policy for the allocation of memory for the compressed data,
instead just adopting the memory policy of the task entering reclaim, or
the default policy (prefer local node) if no such policy is specified. 
This can lead to several pathological behaviors in multi-node NUMA
systems:

1. Systems with CXL-based memory tiering can encounter the following
   inversion with zswap/zram: the coldest pages demoted to the CXL tier
   can return to the high tier when they are reclaimed to compressed swap,
   creating memory pressure on the high tier.

2. Consider a direct reclaimer scanning nodes in order of allocation
   preference.  If it ventures into remote nodes, the memory it compresses
   there should stay there.  Trying to shift those contents over to the
   reclaiming thread's preferred node further *increases* its local
   pressure, and provoking more spills.  The remote node is also the most
   likely to refault this data again.  This undesirable behavior was
   pointed out by Johannes Weiner in [1].

3. For zswap writeback, the zswap entries are organized in
   node-specific LRUs, based on the node placement of the original pages,
   allowing for targeted zswap writeback for specific nodes.

   However, the compressed data of a zswap entry can be placed on a
   different node from the LRU it is placed on.  This means that reclaim
   targeted at one node might not free up memory used for zswap entries in
   that node, but instead reclaiming memory in a different node.

All of these issues will be resolved if the compressed data go to the same
node as the original page.  This patch encourages this behavior by having
zswap and zram pass the node of the original page to zsmalloc, and have
zsmalloc prefer the specified node if we need to allocate new (zs)pages
for the compressed data.

Note that we are not strictly binding the allocation to the preferred
node.  We still allow the allocation to fall back to other nodes when the
preferred node is full, or if we have zspages with slots available on a
different node.  This is OK, and still a strict improvement over the
status quo:

1. On a system with demotion enabled, we will generally prefer
   demotions over compressed swapping, and only swap when pages have
   already gone to the lowest tier.  This patch should achieve the desired
   effect for the most part.

2. If the preferred node is out of memory, letting the compressed data
   going to other nodes can be better than the alternative (OOMs, keeping
   cold memory unreclaimed, disk swapping, etc.).

3. If the allocation go to a separate node because we have a zspage
   with slots available, at least we're not creating extra immediate
   memory pressure (since the space is already allocated).

3. While there can be mixings, we generally reclaim pages in same-node
   batches, which encourage zspage grouping that is more likely to go to
   the right node.

4. A strict binding would require partitioning zsmalloc by node, which
   is more complicated, and more prone to regression, since it reduces the
   storage density of zsmalloc.  We need to evaluate the tradeoff and
   benchmark carefully before adopting such an involved solution.

[1]: https://lore.kernel.org/linux-mm/20250331165306.GC2110528@cmpxchg.org/

[senozhatsky@chromium.org: coding-style fixes]
  Link: https://lkml.kernel.org/r/mnvexa7kseswglcqbhlot4zg3b3la2ypv2rimdl5mh5glbmhvz@wi6bgqn47hge
Link: https://lkml.kernel.org/r/20250402204416.3435994-1-nphamcs@gmail.com
Signed-off-by: Nhat Pham <nphamcs@gmail.com>
Suggested-by: Gregory Price <gourry@gourry.net>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev>
Acked-by: Sergey Senozhatsky <senozhatsky@chromium.org>	[zram, zsmalloc]
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Yosry Ahmed <yosry.ahmed@linux.dev>	[zswap/zsmalloc]
Cc: "Huang, Ying" <ying.huang@linux.alibaba.com>
Cc: Joanthan Cameron <Jonathan.Cameron@huawei.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: SeongJae Park <sj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

3 files changed, 17 insertions, 13 deletions

diff --git a/mm/zpool.c b/mm/zpool.c
index 6d6d88930932..0a71d03369f1 100644
--- a/mm/zpool.c
+++ b/mm/zpool.c
@@ -226,20 +226,22 @@ const char *zpool_get_type(struct zpool *zpool)
  * @size:	The amount of memory to allocate.
  * @gfp:	The GFP flags to use when allocating memory.
  * @handle:	Pointer to the handle to set
+ * @nid:	The preferred node id.
  *
  * This allocates the requested amount of memory from the pool.
  * The gfp flags will be used when allocating memory, if the
  * implementation supports it.  The provided @handle will be
- * set to the allocated object handle.
+ * set to the allocated object handle. The allocation will
+ * prefer the NUMA node specified by @nid.
  *
  * Implementations must guarantee this to be thread-safe.
  *
  * Returns: 0 on success, negative value on error.
  */
 int zpool_malloc(struct zpool *zpool, size_t size, gfp_t gfp,
-			unsigned long *handle)
+		 unsigned long *handle, const int nid)
 {
-	return zpool->driver->malloc(zpool->pool, size, gfp, handle);
+	return zpool->driver->malloc(zpool->pool, size, gfp, handle, nid);
 }
 
 /**
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index d14a7e317ac8..513b08c7c941 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -243,9 +243,9 @@ static inline void zpdesc_dec_zone_page_state(struct zpdesc *zpdesc)
 	dec_zone_page_state(zpdesc_page(zpdesc), NR_ZSPAGES);
 }
 
-static inline struct zpdesc *alloc_zpdesc(gfp_t gfp)
+static inline struct zpdesc *alloc_zpdesc(gfp_t gfp, const int nid)
 {
-	struct page *page = alloc_page(gfp);
+	struct page *page = alloc_pages_node(nid, gfp, 0);
 
 	return page_zpdesc(page);
 }
@@ -462,9 +462,9 @@ static void zs_zpool_destroy(void *pool)
 }
 
 static int zs_zpool_malloc(void *pool, size_t size, gfp_t gfp,
-			unsigned long *handle)
+			   unsigned long *handle, const int nid)
 {
-	*handle = zs_malloc(pool, size, gfp);
+	*handle = zs_malloc(pool, size, gfp, nid);
 
 	if (IS_ERR_VALUE(*handle))
 		return PTR_ERR((void *)*handle);
@@ -1043,8 +1043,8 @@ static void create_page_chain(struct size_class *class, struct zspage *zspage,
  * Allocate a zspage for the given size class
  */
 static struct zspage *alloc_zspage(struct zs_pool *pool,
-					struct size_class *class,
-					gfp_t gfp)
+				   struct size_class *class,
+				   gfp_t gfp, const int nid)
 {
 	int i;
 	struct zpdesc *zpdescs[ZS_MAX_PAGES_PER_ZSPAGE];
@@ -1061,7 +1061,7 @@ static struct zspage *alloc_zspage(struct zs_pool *pool,
 	for (i = 0; i < class->pages_per_zspage; i++) {
 		struct zpdesc *zpdesc;
 
-		zpdesc = alloc_zpdesc(gfp);
+		zpdesc = alloc_zpdesc(gfp, nid);
 		if (!zpdesc) {
 			while (--i >= 0) {
 				zpdesc_dec_zone_page_state(zpdescs[i]);
@@ -1336,12 +1336,14 @@ static unsigned long obj_malloc(struct zs_pool *pool,
  * @pool: pool to allocate from
  * @size: size of block to allocate
  * @gfp: gfp flags when allocating object
+ * @nid: The preferred node id to allocate new zspage (if needed)
  *
  * On success, handle to the allocated object is returned,
  * otherwise an ERR_PTR().
  * Allocation requests with size > ZS_MAX_ALLOC_SIZE will fail.
  */
-unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp)
+unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp,
+			const int nid)
 {
 	unsigned long handle;
 	struct size_class *class;
@@ -1376,7 +1378,7 @@ unsigned long zs_malloc(struct zs_pool *pool, size_t size, gfp_t gfp)
 
 	spin_unlock(&class->lock);
 
-	zspage = alloc_zspage(pool, class, gfp);
+	zspage = alloc_zspage(pool, class, gfp, nid);
 	if (!zspage) {
 		cache_free_handle(pool, handle);
 		return (unsigned long)ERR_PTR(-ENOMEM);
diff --git a/mm/zswap.c b/mm/zswap.c
index 204fb59da33c..455e9425c5f5 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -981,7 +981,7 @@ static bool zswap_compress(struct page *page, struct zswap_entry *entry,
 
 	zpool = pool->zpool;
 	gfp = GFP_NOWAIT | __GFP_NORETRY | __GFP_HIGHMEM | __GFP_MOVABLE;
-	alloc_ret = zpool_malloc(zpool, dlen, gfp, &handle);
+	alloc_ret = zpool_malloc(zpool, dlen, gfp, &handle, page_to_nid(page));
 	if (alloc_ret)
 		goto unlock;