mm: zpool: add interfaces for object read/write APIs

Patch series "Switch zswap to object read/write APIs".

This patch series updates zswap to use the new object read/write APIs
defined by zsmalloc in [1], and remove the old object mapping APIs and the
related code from zpool and zsmalloc.


This patch (of 5):

Zsmalloc introduced new APIs to read/write objects besides mapping them. 
Add the necessary zpool interfaces.

Link: https://lkml.kernel.org/r/20250305061134.4105762-1-yosry.ahmed@linux.dev
Link: https://lkml.kernel.org/r/20250305061134.4105762-2-yosry.ahmed@linux.dev
Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Nhat Pham <nphamcs@gmail.com>
Cc: Chengming Zhou <chengming.zhou@linux.dev>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/zpool.h

@@ -52,6 +52,16 @@ void *zpool_map_handle(struct zpool *pool, unsigned long handle,
 
 void zpool_unmap_handle(struct zpool *pool, unsigned long handle);
 
+
+void *zpool_obj_read_begin(struct zpool *zpool, unsigned long handle,
+			   void *local_copy);
+
+void zpool_obj_read_end(struct zpool *zpool, unsigned long handle,
+			void *handle_mem);
+
+void zpool_obj_write(struct zpool *zpool, unsigned long handle,
+		     void *handle_mem, size_t mem_len);
+
 u64 zpool_get_total_pages(struct zpool *pool);
 
 
@@ -90,6 +100,13 @@ struct zpool_driver {
 				enum zpool_mapmode mm);
 	void (*unmap)(void *pool, unsigned long handle);
 
+	void *(*obj_read_begin)(void *pool, unsigned long handle,
+				void *local_copy);
+	void (*obj_read_end)(void *pool, unsigned long handle,
+			     void *handle_mem);
+	void (*obj_write)(void *pool, unsigned long handle,
+			  void *handle_mem, size_t mem_len);
+
 	u64 (*total_pages)(void *pool);
 };
 

mm/zpool.c

@@ -320,6 +320,54 @@ void zpool_unmap_handle(struct zpool *zpool, unsigned long handle)
 	zpool->driver->unmap(zpool->pool, handle);
 }
 
+/**
+ * zpool_obj_read_begin() - Start reading from a previously allocated handle.
+ * @zpool:	The zpool that the handle was allocated from
+ * @handle:	The handle to read from
+ * @local_copy:	A local buffer to use if needed.
+ *
+ * This starts a read operation of a previously allocated handle. The passed
+ * @local_copy buffer may be used if needed by copying the memory into.
+ * zpool_obj_read_end() MUST be called after the read is completed to undo any
+ * actions taken (e.g. release locks).
+ *
+ * Returns: A pointer to the handle memory to be read, if @local_copy is used,
+ * the returned pointer is @local_copy.
+ */
+void *zpool_obj_read_begin(struct zpool *zpool, unsigned long handle,
+			   void *local_copy)
+{
+	return zpool->driver->obj_read_begin(zpool->pool, handle, local_copy);
+}
+
+/**
+ * zpool_obj_read_end() - Finish reading from a previously allocated handle.
+ * @zpool:	The zpool that the handle was allocated from
+ * @handle:	The handle to read from
+ * @handle_mem:	The pointer returned by zpool_obj_read_begin()
+ *
+ * Finishes a read operation previously started by zpool_obj_read_begin().
+ */
+void zpool_obj_read_end(struct zpool *zpool, unsigned long handle,
+			void *handle_mem)
+{
+	zpool->driver->obj_read_end(zpool->pool, handle, handle_mem);
+}
+
+/**
+ * zpool_obj_write() - Write to a previously allocated handle.
+ * @zpool:	The zpool that the handle was allocated from
+ * @handle:	The handle to read from
+ * @handle_mem:	The memory to copy from into the handle.
+ * @mem_len:	The length of memory to be written.
+ *
+ */
+void zpool_obj_write(struct zpool *zpool, unsigned long handle,
+		     void *handle_mem, size_t mem_len)
+{
+	zpool->driver->obj_write(zpool->pool, handle, handle_mem, mem_len);
+}
+
 /**
  * zpool_get_total_pages() - The total size of the pool
  * @zpool:	The zpool to check

mm/zsmalloc.c

@@ -507,6 +507,24 @@ static void zs_zpool_unmap(void *pool, unsigned long handle)
 	zs_unmap_object(pool, handle);
 }
 
+static void *zs_zpool_obj_read_begin(void *pool, unsigned long handle,
+				     void *local_copy)
+{
+	return zs_obj_read_begin(pool, handle, local_copy);
+}
+
+static void zs_zpool_obj_read_end(void *pool, unsigned long handle,
+				  void *handle_mem)
+{
+	zs_obj_read_end(pool, handle, handle_mem);
+}
+
+static void zs_zpool_obj_write(void *pool, unsigned long handle,
+			       void *handle_mem, size_t mem_len)
+{
+	zs_obj_write(pool, handle, handle_mem, mem_len);
+}
+
 static u64 zs_zpool_total_pages(void *pool)
 {
 	return zs_get_total_pages(pool);
@@ -522,6 +540,9 @@ static struct zpool_driver zs_zpool_driver = {
 	.free =			  zs_zpool_free,
 	.map =			  zs_zpool_map,
 	.unmap =		  zs_zpool_unmap,
+	.obj_read_begin =	  zs_zpool_obj_read_begin,
+	.obj_read_end  =	  zs_zpool_obj_read_end,
+	.obj_write =		  zs_zpool_obj_write,
 	.total_pages =		  zs_zpool_total_pages,
 };