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/[email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Hugh Dickins <[email protected]>
Reviewed-by: Chuck Lever <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Cc: Axel Rasmussen <[email protected]>
Cc: Carlos Maiolino <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Darrick J. Wong <[email protected]>
Cc: Dave Chinner <[email protected]>
Cc: Tim Chen <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

1 files changed, 10 insertions, 6 deletions

diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index 6b0c626620f5..2caa6b86106a 100644
--- a/include/linux/shmem_fs.h
+++ b/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;
 };