svn commit: r363891 - head/sys/kern

[Don Lewis]

On  5 Aug, Mateusz Guzik wrote:
> Author: mjg
> Date: Wed Aug  5 09:24:38 2020
> New Revision: 363891
> URL: https://svnweb.freebsd.org/changeset/base/363891
> 
> Log:
>   cache: reduce zone alignment to 8 bytes
>   
>   It used to be sizeof of the given struct to accomodate for 32 bit mips
>   doing 64 bit loads, but the same can be achieved with requireing just
>   64 bit alignment.
>   
>   While here reorder struct namecache so that most commonly used fields
>   are closer.
> 
> Modified:
>   head/sys/kern/vfs_cache.c
> 
> Modified: head/sys/kern/vfs_cache.c
> ==============================================================================
> --- head/sys/kern/vfs_cache.c	Wed Aug  5 09:24:00 2020	(r363890)
> +++ head/sys/kern/vfs_cache.c	Wed Aug  5 09:24:38 2020	(r363891)
> @@ -122,9 +122,9 @@ _Static_assert(sizeof(struct negstate) <= sizeof(struc
>      "the state must fit in a union with a pointer without growing it");
>  
>  struct	namecache {
> -	CK_LIST_ENTRY(namecache) nc_hash;/* hash chain */
>  	LIST_ENTRY(namecache) nc_src;	/* source vnode list */
>  	TAILQ_ENTRY(namecache) nc_dst;	/* destination vnode list */
> +	CK_LIST_ENTRY(namecache) nc_hash;/* hash chain */
>  	struct	vnode *nc_dvp;		/* vnode of parent of name */
>  	union {
>  		struct	vnode *nu_vp;	/* vnode the name refers to */
> @@ -142,6 +142,8 @@ struct	namecache {
>   * to be stored.  The nc_dotdottime field is used when a cache entry is mapping
>   * both a non-dotdot directory name plus dotdot for the directory's
>   * parent.
> + *
> + * See below for alignment requirement.
>   */
>  struct	namecache_ts {
>  	struct	timespec nc_time;	/* timespec provided by fs */
> @@ -150,6 +152,14 @@ struct	namecache_ts {
>  	struct namecache nc_nc;
>  };
>  
> +/*
> + * At least mips n32 performs 64-bit accesses to timespec as found
> + * in namecache_ts and requires them to be aligned. Since others
> + * may be in the same spot suffer a little bit and enforce the
> + * alignment for everyone. Note this is a nop for 64-bit platforms.
> + */
> +#define CACHE_ZONE_ALIGNMENT	UMA_ALIGNOF(time_t)

time_t is only 32 bits on i386