mm: add comments for allocation helpers explaining why they are macros

A number of allocation helper functions were converted into macros to
account them at the call sites.  Add a comment for each converted
allocation helper explaining why it has to be a macro and why we typecast
the return value wherever required.  The patch also moves
acpi_os_acquire_object() closer to other allocation helpers to group them
together under the same comment.  The patch has no functional changes.

Link: https://lkml.kernel.org/r/20240703174225.3891393-1-surenb@google.com
Fixes: 2c321f3f70 ("mm: change inlined allocation helpers to account at the call site")
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Suggested-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Christian König <christian.koenig@amd.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jan Kara <jack@suse.cz>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Thorsten Blum <thorsten.blum@toblux.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/nfs/iostat.h

@@ -46,6 +46,10 @@ static inline void nfs_add_stats(const struct inode *inode,
 	nfs_add_server_stats(NFS_SERVER(inode), stat, addend);
 }
 
+/*
+ * This specialized allocator has to be a macro for its allocations to be
+ * accounted separately (to have a separate alloc_tag).
+ */
 #define nfs_alloc_iostats()	alloc_percpu(struct nfs_iostats)
 
 static inline void nfs_free_iostats(struct nfs_iostats __percpu *stats)

include/acpi/platform/aclinuxex.h

@@ -46,6 +46,9 @@ acpi_status acpi_os_terminate(void);
  * Interrupts are off during resume, just like they are for boot.
  * However, boot has  (system_state != SYSTEM_RUNNING)
  * to quiet __might_sleep() in kmalloc() and resume does not.
+ *
+ * These specialized allocators have to be macros for their allocations to be
+ * accounted separately (to have separate alloc_tag).
  */
 #define acpi_os_allocate(_size)	\
 		kmalloc(_size, irqs_disabled() ? GFP_ATOMIC : GFP_KERNEL)
@@ -53,14 +56,14 @@ acpi_status acpi_os_terminate(void);
 #define acpi_os_allocate_zeroed(_size)	\
 		kzalloc(_size, irqs_disabled() ? GFP_ATOMIC : GFP_KERNEL)
 
+#define acpi_os_acquire_object(_cache)	\
+		kmem_cache_zalloc(_cache, irqs_disabled() ? GFP_ATOMIC : GFP_KERNEL)
+
 static inline void acpi_os_free(void *memory)
 {
 	kfree(memory);
 }
 
-#define acpi_os_acquire_object(_cache)	\
-		kmem_cache_zalloc(_cache, irqs_disabled() ? GFP_ATOMIC : GFP_KERNEL)
-
 static inline acpi_thread_id acpi_os_get_thread_id(void)
 {
 	return (acpi_thread_id) (unsigned long)current;

include/linux/bpf.h

@@ -2261,6 +2261,10 @@ void *bpf_map_kvcalloc(struct bpf_map *map, size_t n, size_t size,
 void __percpu *bpf_map_alloc_percpu(const struct bpf_map *map, size_t size,
 				    size_t align, gfp_t flags);
 #else
+/*
+ * These specialized allocators have to be macros for their allocations to be
+ * accounted separately (to have separate alloc_tag).
+ */
 #define bpf_map_kmalloc_node(_map, _size, _flags, _node)	\
 		kmalloc_node(_size, _flags, _node)
 #define bpf_map_kzalloc(_map, _size, _flags)			\

include/linux/dma-fence-chain.h

@@ -85,6 +85,10 @@ dma_fence_chain_contained(struct dma_fence *fence)
  * dma_fence_chain_alloc
  *
  * Returns a new struct dma_fence_chain object or NULL on failure.
+ *
+ * This specialized allocator has to be a macro for its allocations to be
+ * accounted separately (to have a separate alloc_tag). The typecast is
+ * intentional to enforce typesafety.
  */
 #define dma_fence_chain_alloc()	\
 		((struct dma_fence_chain *)kmalloc(sizeof(struct dma_fence_chain), GFP_KERNEL))

include/linux/hid_bpf.h

@@ -152,6 +152,11 @@ static inline int hid_bpf_connect_device(struct hid_device *hdev) { return 0; }
 static inline void hid_bpf_disconnect_device(struct hid_device *hdev) {}
 static inline void hid_bpf_destroy_device(struct hid_device *hid) {}
 static inline void hid_bpf_device_init(struct hid_device *hid) {}
+/*
+ * This specialized allocator has to be a macro for its allocations to be
+ * accounted separately (to have a separate alloc_tag). The typecast is
+ * intentional to enforce typesafety.
+ */
 #define call_hid_bpf_rdesc_fixup(_hdev, _rdesc, _size)	\
 		((u8 *)kmemdup(_rdesc, *(_size), GFP_KERNEL))
 

include/linux/jbd2.h

@@ -1588,6 +1588,11 @@ void jbd2_journal_put_journal_head(struct journal_head *jh);
  */
 extern struct kmem_cache *jbd2_handle_cache;
 
+/*
+ * This specialized allocator has to be a macro for its allocations to be
+ * accounted separately (to have a separate alloc_tag). The typecast is
+ * intentional to enforce typesafety.
+ */
 #define jbd2_alloc_handle(_gfp_flags)	\
 		((handle_t *)kmem_cache_zalloc(jbd2_handle_cache, _gfp_flags))
 
@@ -1602,6 +1607,11 @@ static inline void jbd2_free_handle(handle_t *handle)
  */
 extern struct kmem_cache *jbd2_inode_cache;
 
+/*
+ * This specialized allocator has to be a macro for its allocations to be
+ * accounted separately (to have a separate alloc_tag). The typecast is
+ * intentional to enforce typesafety.
+ */
 #define jbd2_alloc_inode(_gfp_flags)	\
 		((struct jbd2_inode *)kmem_cache_alloc(jbd2_inode_cache, _gfp_flags))
 

include/linux/skbuff.h

@@ -3400,6 +3400,10 @@ static inline struct page *__dev_alloc_pages_noprof(gfp_t gfp_mask,
 }
 #define __dev_alloc_pages(...)	alloc_hooks(__dev_alloc_pages_noprof(__VA_ARGS__))
 
+/*
+ * This specialized allocator has to be a macro for its allocations to be
+ * accounted separately (to have a separate alloc_tag).
+ */
 #define dev_alloc_pages(_order) __dev_alloc_pages(GFP_ATOMIC | __GFP_NOWARN, _order)
 
 /**
@@ -3416,6 +3420,10 @@ static inline struct page *__dev_alloc_page_noprof(gfp_t gfp_mask)
 }
 #define __dev_alloc_page(...)	alloc_hooks(__dev_alloc_page_noprof(__VA_ARGS__))
 
+/*
+ * This specialized allocator has to be a macro for its allocations to be
+ * accounted separately (to have a separate alloc_tag).
+ */
 #define dev_alloc_page()	dev_alloc_pages(0)
 
 /**

include/linux/skmsg.h

@@ -414,6 +414,11 @@ void sk_psock_stop_verdict(struct sock *sk, struct sk_psock *psock);
 int sk_psock_msg_verdict(struct sock *sk, struct sk_psock *psock,
 			 struct sk_msg *msg);
 
+/*
+ * This specialized allocator has to be a macro for its allocations to be
+ * accounted separately (to have a separate alloc_tag). The typecast is
+ * intentional to enforce typesafety.
+ */
 #define sk_psock_init_link()	\
 		((struct sk_psock_link *)kzalloc(sizeof(struct sk_psock_link),	\
 						 GFP_ATOMIC | __GFP_NOWARN))