mm/shmem.c: make shmem_mapping() inline

shmem_mapping() isn't worth an out-of-line call from any callsite.

So make it inline by
 - make shmem_aops global
 - export shmem_aops
 - inline the shmem_mapping()

and replace the direct call 'shmem_aops' with shmem_mapping()
in shmem.c.

Link: https://lkml.kernel.org/r/20201115165207.GA265355@rlkSigned-off-by: Hui Su <sh_def@163.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/shmem_fs.h

@@ -67,7 +67,11 @@ extern unsigned long shmem_get_unmapped_area(struct file *, unsigned long addr,
 		unsigned long len, unsigned long pgoff, unsigned long flags);
 extern int shmem_lock(struct file *file, int lock, struct user_struct *user);
 #ifdef CONFIG_SHMEM
-extern bool shmem_mapping(struct address_space *mapping);
+extern const struct address_space_operations shmem_aops;
+static inline bool shmem_mapping(struct address_space *mapping)
+{
+	return mapping->a_ops == &shmem_aops;
+}
 #else
 static inline bool shmem_mapping(struct address_space *mapping)
 {

mm/shmem.c

@@ -246,7 +246,7 @@ static inline void shmem_inode_unacct_blocks(struct inode *inode, long pages)
 }
 
 static const struct super_operations shmem_ops;
-static const struct address_space_operations shmem_aops;
+const struct address_space_operations shmem_aops;
 static const struct file_operations shmem_file_operations;
 static const struct inode_operations shmem_inode_operations;
 static const struct inode_operations shmem_dir_inode_operations;
@@ -1152,7 +1152,7 @@ static void shmem_evict_inode(struct inode *inode)
 	struct shmem_inode_info *info = SHMEM_I(inode);
 	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
 
-	if (inode->i_mapping->a_ops == &shmem_aops) {
+	if (shmem_mapping(inode->i_mapping)) {
 		shmem_unacct_size(info->flags, inode->i_size);
 		inode->i_size = 0;
 		shmem_truncate_range(inode, 0, (loff_t)-1);
@@ -1858,7 +1858,7 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
 	}
 
 	/* shmem_symlink() */
-	if (mapping->a_ops != &shmem_aops)
+	if (!shmem_mapping(mapping))
 		goto alloc_nohuge;
 	if (shmem_huge == SHMEM_HUGE_DENY || sgp_huge == SGP_NOHUGE)
 		goto alloc_nohuge;
@@ -2352,11 +2352,6 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
 	return inode;
 }
 
-bool shmem_mapping(struct address_space *mapping)
-{
-	return mapping->a_ops == &shmem_aops;
-}
-
 static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
 				  pmd_t *dst_pmd,
 				  struct vm_area_struct *dst_vma,
@@ -3865,7 +3860,7 @@ static void shmem_destroy_inodecache(void)
 	kmem_cache_destroy(shmem_inode_cachep);
 }
 
-static const struct address_space_operations shmem_aops = {
+const struct address_space_operations shmem_aops = {
 	.writepage	= shmem_writepage,
 	.set_page_dirty	= __set_page_dirty_no_writeback,
 #ifdef CONFIG_TMPFS
@@ -3877,6 +3872,7 @@ static const struct address_space_operations shmem_aops = {
 #endif
 	.error_remove_page = generic_error_remove_page,
 };
+EXPORT_SYMBOL(shmem_aops);
 
 static const struct file_operations shmem_file_operations = {
 	.mmap		= shmem_mmap,
@@ -4312,7 +4308,7 @@ struct page *shmem_read_mapping_page_gfp(struct address_space *mapping,
 	struct page *page;
 	int error;
 
-	BUG_ON(mapping->a_ops != &shmem_aops);
+	BUG_ON(!shmem_mapping(mapping));
 	error = shmem_getpage_gfp(inode, index, &page, SGP_CACHE,
 				  gfp, NULL, NULL, NULL);
 	if (error)