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remove whole-process swapping
Long before Unix supported paging, it used process swapping to reclaim
memory.  The code is there and in theory it runs when we get *extremely* low
on memory.  In practice, it never runs since the definition of low-on-memory
is antiquated. (XXX: define what antiquated means)
You can check the number of swapout/swapin events with kstats:
$ kstat -p ::vm:swapin ::vm:swapout
remove xhat
The xhat infrastructure was added to support hardware such as the zulu
graphics card - hardware which had on-board MMUs.  The VM used the xhat code
to keep the CPU's and Zulu's page tables in-sync.  Since the only xhat user
was zulu (which is gone), we can safely remove it simplifying the whole VM
subsystem.
Assorted notes:
- AS_BUSY flag was used solely by xhat


 108         kmutex_t a_contents;    /* protect certain fields in the structure */
 109         uchar_t  a_flags;       /* as attributes */
 110         uchar_t a_vbits;        /* used for collecting statistics */
 111         kcondvar_t a_cv;        /* used by as_rangelock */
 112         struct  hat *a_hat;     /* hat structure */
 113         struct  hrmstat *a_hrm; /* ref and mod bits */
 114         caddr_t a_userlimit;    /* highest allowable address in this as */
 115         struct seg *a_seglast;  /* last segment hit on the addr space */
 116         krwlock_t a_lock;       /* protects segment related fields */
 117         size_t  a_size;         /* total size of address space */
 118         struct seg *a_lastgap;  /* last seg found by as_gap() w/ AS_HI (mmap) */
 119         struct seg *a_lastgaphl; /* last seg saved in as_gap() either for */
 120                                 /* AS_HI or AS_LO used in as_addseg() */
 121         avl_tree_t a_segtree;   /* segments in this address space. (AVL tree) */
 122         avl_tree_t a_wpage;     /* watched pages (procfs) */
 123         uchar_t a_updatedir;    /* mappings changed, rebuild a_objectdir */
 124         timespec_t a_updatetime;        /* time when mappings last changed */
 125         vnode_t **a_objectdir;  /* object directory (procfs) */
 126         size_t  a_sizedir;      /* size of object directory */
 127         struct as_callback *a_callbacks; /* callback list */
 128         void *a_xhat;           /* list of xhat providers */
 129         proc_t  *a_proc;        /* back pointer to proc */
 130         size_t  a_resvsize;     /* size of reserved part of address space */
 131 };
 132 
 133 #define AS_PAGLCK               0x80
 134 #define AS_CLAIMGAP             0x40
 135 #define AS_UNMAPWAIT            0x20
 136 #define AS_NEEDSPURGE           0x10    /* mostly for seg_nf, see as_purge() */
 137 #define AS_NOUNMAPWAIT          0x02
 138 #define AS_BUSY                 0x01    /* needed by XHAT framework */
 139 
 140 #define AS_ISPGLCK(as)          ((as)->a_flags & AS_PAGLCK)
 141 #define AS_ISCLAIMGAP(as)       ((as)->a_flags & AS_CLAIMGAP)
 142 #define AS_ISUNMAPWAIT(as)      ((as)->a_flags & AS_UNMAPWAIT)
 143 #define AS_ISBUSY(as)           ((as)->a_flags & AS_BUSY)
 144 #define AS_ISNOUNMAPWAIT(as)    ((as)->a_flags & AS_NOUNMAPWAIT)
 145 
 146 #define AS_SETPGLCK(as)         ((as)->a_flags |= AS_PAGLCK)
 147 #define AS_SETCLAIMGAP(as)      ((as)->a_flags |= AS_CLAIMGAP)
 148 #define AS_SETUNMAPWAIT(as)     ((as)->a_flags |= AS_UNMAPWAIT)
 149 #define AS_SETBUSY(as)          ((as)->a_flags |= AS_BUSY)
 150 #define AS_SETNOUNMAPWAIT(as)   ((as)->a_flags |= AS_NOUNMAPWAIT)
 151 
 152 #define AS_CLRPGLCK(as)         ((as)->a_flags &= ~AS_PAGLCK)
 153 #define AS_CLRCLAIMGAP(as)      ((as)->a_flags &= ~AS_CLAIMGAP)
 154 #define AS_CLRUNMAPWAIT(as)     ((as)->a_flags &= ~AS_UNMAPWAIT)
 155 #define AS_CLRBUSY(as)          ((as)->a_flags &= ~AS_BUSY)
 156 #define AS_CLRNOUNMAPWAIT(as)   ((as)->a_flags &= ~AS_NOUNMAPWAIT)
 157 
 158 #define AS_TYPE_64BIT(as)       \
 159             (((as)->a_userlimit > (caddr_t)UINT32_MAX) ? 1 : 0)
 160 
 161 /*
 162  * Flags for as_map/as_map_ansegs
 163  */
 164 #define AS_MAP_NO_LPOOB         ((uint_t)-1)
 165 #define AS_MAP_HEAP             ((uint_t)-2)
 166 #define AS_MAP_STACK            ((uint_t)-3)
 167 
 168 /*
 169  * The as_callback is the basic structure which supports the ability to
 170  * inform clients of specific events pertaining to address space management.
 171  * A user calls as_add_callback to register an address space callback
 172  * for a range of pages, specifying the events that need to occur.
 173  * When as_do_callbacks is called and finds a 'matching' entry, the
 174  * callback is called once, and the callback function MUST call
 175  * as_delete_callback when all callback activities are complete.


 271 int     as_dup(struct as *as, struct proc *forkedproc);
 272 struct  seg *as_findseg(struct as *as, caddr_t addr, int tail);
 273 int     as_addseg(struct as *as, struct seg *newseg);
 274 struct  seg *as_removeseg(struct as *as, struct seg *seg);
 275 faultcode_t as_fault(struct hat *hat, struct as *as, caddr_t addr, size_t size,
 276                 enum fault_type type, enum seg_rw rw);
 277 faultcode_t as_faulta(struct as *as, caddr_t addr, size_t size);
 278 int     as_setprot(struct as *as, caddr_t addr, size_t size, uint_t prot);
 279 int     as_checkprot(struct as *as, caddr_t addr, size_t size, uint_t prot);
 280 int     as_unmap(struct as *as, caddr_t addr, size_t size);
 281 int     as_map(struct as *as, caddr_t addr, size_t size, int ((*crfp)()),
 282                 void *argsp);
 283 void    as_purge(struct as *as);
 284 int     as_gap(struct as *as, size_t minlen, caddr_t *basep, size_t *lenp,
 285                 uint_t flags, caddr_t addr);
 286 int     as_gap_aligned(struct as *as, size_t minlen, caddr_t *basep,
 287             size_t *lenp, uint_t flags, caddr_t addr, size_t align,
 288             size_t redzone, size_t off);
 289 
 290 int     as_memory(struct as *as, caddr_t *basep, size_t *lenp);
 291 size_t  as_swapout(struct as *as);
 292 int     as_incore(struct as *as, caddr_t addr, size_t size, char *vec,
 293                 size_t *sizep);
 294 int     as_ctl(struct as *as, caddr_t addr, size_t size, int func, int attr,
 295                 uintptr_t arg, ulong_t *lock_map, size_t pos);
 296 int     as_pagelock(struct as *as, struct page ***ppp, caddr_t addr,
 297                 size_t size, enum seg_rw rw);
 298 void    as_pageunlock(struct as *as, struct page **pp, caddr_t addr,
 299                 size_t size, enum seg_rw rw);
 300 int     as_setpagesize(struct as *as, caddr_t addr, size_t size, uint_t szc,
 301                 boolean_t wait);
 302 int     as_set_default_lpsize(struct as *as, caddr_t addr, size_t size);
 303 void    as_setwatch(struct as *as);
 304 void    as_clearwatch(struct as *as);
 305 int     as_getmemid(struct as *, caddr_t, memid_t *);
 306 
 307 int     as_add_callback(struct as *, void (*)(), void *, uint_t,
 308                         caddr_t, size_t, int);
 309 uint_t  as_delete_callback(struct as *, void *);
 310 
 311 #endif  /* _KERNEL */


 108         kmutex_t a_contents;    /* protect certain fields in the structure */
 109         uchar_t  a_flags;       /* as attributes */
 110         uchar_t a_vbits;        /* used for collecting statistics */
 111         kcondvar_t a_cv;        /* used by as_rangelock */
 112         struct  hat *a_hat;     /* hat structure */
 113         struct  hrmstat *a_hrm; /* ref and mod bits */
 114         caddr_t a_userlimit;    /* highest allowable address in this as */
 115         struct seg *a_seglast;  /* last segment hit on the addr space */
 116         krwlock_t a_lock;       /* protects segment related fields */
 117         size_t  a_size;         /* total size of address space */
 118         struct seg *a_lastgap;  /* last seg found by as_gap() w/ AS_HI (mmap) */
 119         struct seg *a_lastgaphl; /* last seg saved in as_gap() either for */
 120                                 /* AS_HI or AS_LO used in as_addseg() */
 121         avl_tree_t a_segtree;   /* segments in this address space. (AVL tree) */
 122         avl_tree_t a_wpage;     /* watched pages (procfs) */
 123         uchar_t a_updatedir;    /* mappings changed, rebuild a_objectdir */
 124         timespec_t a_updatetime;        /* time when mappings last changed */
 125         vnode_t **a_objectdir;  /* object directory (procfs) */
 126         size_t  a_sizedir;      /* size of object directory */
 127         struct as_callback *a_callbacks; /* callback list */

 128         proc_t  *a_proc;        /* back pointer to proc */
 129         size_t  a_resvsize;     /* size of reserved part of address space */
 130 };
 131 
 132 #define AS_PAGLCK               0x80
 133 #define AS_CLAIMGAP             0x40
 134 #define AS_UNMAPWAIT            0x20
 135 #define AS_NEEDSPURGE           0x10    /* mostly for seg_nf, see as_purge() */
 136 #define AS_NOUNMAPWAIT          0x02

 137 
 138 #define AS_ISPGLCK(as)          ((as)->a_flags & AS_PAGLCK)
 139 #define AS_ISCLAIMGAP(as)       ((as)->a_flags & AS_CLAIMGAP)
 140 #define AS_ISUNMAPWAIT(as)      ((as)->a_flags & AS_UNMAPWAIT)

 141 #define AS_ISNOUNMAPWAIT(as)    ((as)->a_flags & AS_NOUNMAPWAIT)
 142 
 143 #define AS_SETPGLCK(as)         ((as)->a_flags |= AS_PAGLCK)
 144 #define AS_SETCLAIMGAP(as)      ((as)->a_flags |= AS_CLAIMGAP)
 145 #define AS_SETUNMAPWAIT(as)     ((as)->a_flags |= AS_UNMAPWAIT)

 146 #define AS_SETNOUNMAPWAIT(as)   ((as)->a_flags |= AS_NOUNMAPWAIT)
 147 
 148 #define AS_CLRPGLCK(as)         ((as)->a_flags &= ~AS_PAGLCK)
 149 #define AS_CLRCLAIMGAP(as)      ((as)->a_flags &= ~AS_CLAIMGAP)
 150 #define AS_CLRUNMAPWAIT(as)     ((as)->a_flags &= ~AS_UNMAPWAIT)

 151 #define AS_CLRNOUNMAPWAIT(as)   ((as)->a_flags &= ~AS_NOUNMAPWAIT)
 152 
 153 #define AS_TYPE_64BIT(as)       \
 154             (((as)->a_userlimit > (caddr_t)UINT32_MAX) ? 1 : 0)
 155 
 156 /*
 157  * Flags for as_map/as_map_ansegs
 158  */
 159 #define AS_MAP_NO_LPOOB         ((uint_t)-1)
 160 #define AS_MAP_HEAP             ((uint_t)-2)
 161 #define AS_MAP_STACK            ((uint_t)-3)
 162 
 163 /*
 164  * The as_callback is the basic structure which supports the ability to
 165  * inform clients of specific events pertaining to address space management.
 166  * A user calls as_add_callback to register an address space callback
 167  * for a range of pages, specifying the events that need to occur.
 168  * When as_do_callbacks is called and finds a 'matching' entry, the
 169  * callback is called once, and the callback function MUST call
 170  * as_delete_callback when all callback activities are complete.


 266 int     as_dup(struct as *as, struct proc *forkedproc);
 267 struct  seg *as_findseg(struct as *as, caddr_t addr, int tail);
 268 int     as_addseg(struct as *as, struct seg *newseg);
 269 struct  seg *as_removeseg(struct as *as, struct seg *seg);
 270 faultcode_t as_fault(struct hat *hat, struct as *as, caddr_t addr, size_t size,
 271                 enum fault_type type, enum seg_rw rw);
 272 faultcode_t as_faulta(struct as *as, caddr_t addr, size_t size);
 273 int     as_setprot(struct as *as, caddr_t addr, size_t size, uint_t prot);
 274 int     as_checkprot(struct as *as, caddr_t addr, size_t size, uint_t prot);
 275 int     as_unmap(struct as *as, caddr_t addr, size_t size);
 276 int     as_map(struct as *as, caddr_t addr, size_t size, int ((*crfp)()),
 277                 void *argsp);
 278 void    as_purge(struct as *as);
 279 int     as_gap(struct as *as, size_t minlen, caddr_t *basep, size_t *lenp,
 280                 uint_t flags, caddr_t addr);
 281 int     as_gap_aligned(struct as *as, size_t minlen, caddr_t *basep,
 282             size_t *lenp, uint_t flags, caddr_t addr, size_t align,
 283             size_t redzone, size_t off);
 284 
 285 int     as_memory(struct as *as, caddr_t *basep, size_t *lenp);

 286 int     as_incore(struct as *as, caddr_t addr, size_t size, char *vec,
 287                 size_t *sizep);
 288 int     as_ctl(struct as *as, caddr_t addr, size_t size, int func, int attr,
 289                 uintptr_t arg, ulong_t *lock_map, size_t pos);
 290 int     as_pagelock(struct as *as, struct page ***ppp, caddr_t addr,
 291                 size_t size, enum seg_rw rw);
 292 void    as_pageunlock(struct as *as, struct page **pp, caddr_t addr,
 293                 size_t size, enum seg_rw rw);
 294 int     as_setpagesize(struct as *as, caddr_t addr, size_t size, uint_t szc,
 295                 boolean_t wait);
 296 int     as_set_default_lpsize(struct as *as, caddr_t addr, size_t size);
 297 void    as_setwatch(struct as *as);
 298 void    as_clearwatch(struct as *as);
 299 int     as_getmemid(struct as *, caddr_t, memid_t *);
 300 
 301 int     as_add_callback(struct as *, void (*)(), void *, uint_t,
 302                         caddr_t, size_t, int);
 303 uint_t  as_delete_callback(struct as *, void *);
 304 
 305 #endif  /* _KERNEL */