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

Jan Kara
2023-10-03T13:06:40Z

On Fri 29-09-23 20:25:38, Hugh Dickins wrote:
> 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>

Looks good to me. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> ---
> 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
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR