[PATCH 1/8] shmem: shrink shmem_inode_info: dir_offsets in a union

Hugh Dickins
2023-09-30T03:25:58Z

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.

Signed-off-by: Hugh Dickins <hughd@google.com>
---
include/linux/shmem_fs.h | 16 ++++++++++------
1 file 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;
};

--
2.35.3