shmem: shrink shmem_inode_info: dir_offsets in a union

Patch series "shmem,tmpfs: general maintenance".

Mostly just cosmetic mods in mm/shmem.c, but the last two enforcing the
"size=" limit better.  8/8 goes into percpu counter territory, and could
stand alone.


This patch (of 8):

Shave 32 bytes off (the 64-bit) shmem_inode_info.  There was a 4-byte
pahole after stop_eviction, better filled by fsflags.  And the 24-byte
dir_offsets can only be used by directories, whereas shrinklist and
swaplist only by shmem_mapping() inodes (regular files or long symlinks):
so put those into a union.  No change in mm/shmem.c is required for this.

Link: https://lkml.kernel.org/r/c7441dc6-f3bb-dd60-c670-9f5cbd9f266@google.com
Link: https://lkml.kernel.org/r/86ebb4b-c571-b9e8-27f5-cb82ec50357e@google.comSigned-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Carlos Maiolino <cem@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Darrick J. Wong <djwong@kernel.org>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Tim Chen <tim.c.chen@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/shmem_fs.h

@@ -23,18 +23,22 @@ struct shmem_inode_info {
 	unsigned long		flags;
 	unsigned long		alloced;	/* data pages alloced to file */
 	unsigned long		swapped;	/* subtotal assigned to swap */
-	pgoff_t			fallocend;	/* highest fallocate endindex */
-	struct list_head        shrinklist;     /* shrinkable hpage inodes */
-	struct list_head	swaplist;	/* chain of maybes on swap */
+	union {
+	    struct offset_ctx	dir_offsets;	/* stable directory offsets */
+	    struct {
+		struct list_head shrinklist;	/* shrinkable hpage inodes */
+		struct list_head swaplist;	/* chain of maybes on swap */
+	    };
+	};
+	struct timespec64	i_crtime;	/* file creation time */
 	struct shared_policy	policy;		/* NUMA memory alloc policy */
 	struct simple_xattrs	xattrs;		/* list of xattrs */
+	pgoff_t			fallocend;	/* highest fallocate endindex */
+	unsigned int		fsflags;	/* for FS_IOC_[SG]ETFLAGS */
 	atomic_t		stop_eviction;	/* hold when working on inode */
-	struct timespec64	i_crtime;	/* file creation time */
-	unsigned int		fsflags;	/* flags for FS_IOC_[SG]ETFLAGS */
 #ifdef CONFIG_TMPFS_QUOTA
 	struct dquot		*i_dquot[MAXQUOTAS];
 #endif
-	struct offset_ctx	dir_offsets;	/* stable entry offsets */
 	struct inode		vfs_inode;
 };