source: trunk/minix/servers/pm/alloc.c@ 22

/* This file is concerned with allocating and freeing arbitrary-size blocks of
 * physical memory on behalf of the FORK and EXEC system calls.  The key data
 * structure used is the hole table, which maintains a list of holes in memory.
 * It is kept sorted in order of increasing memory address. The addresses
 * it contains refers to physical memory, starting at absolute address 0
 * (i.e., they are not relative to the start of PM).  During system
 * initialization, that part of memory containing the interrupt vectors,
 * kernel, and PM are "allocated" to mark them as not available and to
 * remove them from the hole list.
 *
 * The entry points into this file are:
 *   alloc_mem: allocate a given sized chunk of memory
 *   free_mem:  release a previously allocated chunk of memory
 *   mem_init:  initialize the tables when PM start up
 *   max_hole:  returns the largest hole currently available
 *   mem_holes_copy: for outsiders who want a copy of the hole-list
 */

#include "pm.h"
#include <minix/com.h>
#include <minix/callnr.h>
#include <minix/type.h>
#include <minix/config.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include "mproc.h"
#include "../../kernel/const.h"
#include "../../kernel/config.h"
#include "../../kernel/type.h"

#define NIL_HOLE (struct hole *) 0

PRIVATE struct hole hole[_NR_HOLES];
PRIVATE u32_t high_watermark = 0;

PRIVATE struct hole *hole_head; /* pointer to first hole */
PRIVATE struct hole *free_slots;/* ptr to list of unused table slots */
#if ENABLE_SWAP
PRIVATE int swap_fd = -1;       /* file descriptor of open swap file/device */
PRIVATE u32_t swap_offset;      /* offset to start of swap area on swap file */
PRIVATE phys_clicks swap_base;  /* memory offset chosen as swap base */
PRIVATE phys_clicks swap_maxsize;/* maximum amount of swap "memory" possible */
PRIVATE struct mproc *in_queue; /* queue of processes wanting to swap in */
PRIVATE struct mproc *outswap = &mproc[0];       /* outswap candidate? */
#else /* ! ENABLE_SWAP */
#define swap_base ((phys_clicks) -1)
#endif /* ENABLE_SWAP */

FORWARD _PROTOTYPE( void del_slot, (struct hole *prev_ptr, struct hole *hp) );
FORWARD _PROTOTYPE( void merge, (struct hole *hp)                           );
#if ENABLE_SWAP
FORWARD _PROTOTYPE( int swap_out, (void)                                    );
#else
#define swap_out()      (0)
#endif

/*===========================================================================*
 *                              alloc_mem                                    *
 *===========================================================================*/
PUBLIC phys_clicks alloc_mem(clicks)
phys_clicks clicks;             /* amount of memory requested */
{
/* Allocate a block of memory from the free list using first fit. The block
 * consists of a sequence of contiguous bytes, whose length in clicks is
 * given by 'clicks'.  A pointer to the block is returned.  The block is
 * always on a click boundary.  This procedure is called when memory is
 * needed for FORK or EXEC.  Swap other processes out if needed.
 */
  register struct hole *hp, *prev_ptr;
  phys_clicks old_base;

  do {
        prev_ptr = NIL_HOLE;
        hp = hole_head;
        while (hp != NIL_HOLE && hp->h_base < swap_base) {
                if (hp->h_len >= clicks) {
                        /* We found a hole that is big enough.  Use it. */
                        old_base = hp->h_base;  /* remember where it started */
                        hp->h_base += clicks;   /* bite a piece off */
                        hp->h_len -= clicks;    /* ditto */

                        /* Remember new high watermark of used memory. */
                        if(hp->h_base > high_watermark)
                                high_watermark = hp->h_base;

                        /* Delete the hole if used up completely. */
                        if (hp->h_len == 0) del_slot(prev_ptr, hp);

                        /* Return the start address of the acquired block. */
                        return(old_base);
                }

                prev_ptr = hp;
                hp = hp->h_next;
        }
  } while (swap_out());         /* try to swap some other process out */
  return(NO_MEM);
}

/*===========================================================================*
 *                              free_mem                                     *
 *===========================================================================*/
PUBLIC void free_mem(base, clicks)
phys_clicks base;               /* base address of block to free */
phys_clicks clicks;             /* number of clicks to free */
{
/* Return a block of free memory to the hole list.  The parameters tell where
 * the block starts in physical memory and how big it is.  The block is added
 * to the hole list.  If it is contiguous with an existing hole on either end,
 * it is merged with the hole or holes.
 */
  register struct hole *hp, *new_ptr, *prev_ptr;

  if (clicks == 0) return;
  if ( (new_ptr = free_slots) == NIL_HOLE) 
        panic(__FILE__,"hole table full", NO_NUM);
  new_ptr->h_base = base;
  new_ptr->h_len = clicks;
  free_slots = new_ptr->h_next;
  hp = hole_head;

  /* If this block's address is numerically less than the lowest hole currently
   * available, or if no holes are currently available, put this hole on the
   * front of the hole list.
   */
  if (hp == NIL_HOLE || base <= hp->h_base) {
        /* Block to be freed goes on front of the hole list. */
        new_ptr->h_next = hp;
        hole_head = new_ptr;
        merge(new_ptr);
        return;
  }

  /* Block to be returned does not go on front of hole list. */
  prev_ptr = NIL_HOLE;
  while (hp != NIL_HOLE && base > hp->h_base) {
        prev_ptr = hp;
        hp = hp->h_next;
  }

  /* We found where it goes.  Insert block after 'prev_ptr'. */
  new_ptr->h_next = prev_ptr->h_next;
  prev_ptr->h_next = new_ptr;
  merge(prev_ptr);              /* sequence is 'prev_ptr', 'new_ptr', 'hp' */
}

/*===========================================================================*
 *                              del_slot                                     *
 *===========================================================================*/
PRIVATE void del_slot(prev_ptr, hp)
/* pointer to hole entry just ahead of 'hp' */
register struct hole *prev_ptr;
/* pointer to hole entry to be removed */
register struct hole *hp;       
{
/* Remove an entry from the hole list.  This procedure is called when a
 * request to allocate memory removes a hole in its entirety, thus reducing
 * the numbers of holes in memory, and requiring the elimination of one
 * entry in the hole list.
 */
  if (hp == hole_head)
        hole_head = hp->h_next;
  else
        prev_ptr->h_next = hp->h_next;

  hp->h_next = free_slots;
  hp->h_base = hp->h_len = 0;
  free_slots = hp;
}

/*===========================================================================*
 *                              merge                                        *
 *===========================================================================*/
PRIVATE void merge(hp)
register struct hole *hp;       /* ptr to hole to merge with its successors */
{
/* Check for contiguous holes and merge any found.  Contiguous holes can occur
 * when a block of memory is freed, and it happens to abut another hole on
 * either or both ends.  The pointer 'hp' points to the first of a series of
 * three holes that can potentially all be merged together.
 */
  register struct hole *next_ptr;

  /* If 'hp' points to the last hole, no merging is possible.  If it does not,
   * try to absorb its successor into it and free the successor's table entry.
   */
  if ( (next_ptr = hp->h_next) == NIL_HOLE) return;
  if (hp->h_base + hp->h_len == next_ptr->h_base) {
        hp->h_len += next_ptr->h_len;   /* first one gets second one's mem */
        del_slot(hp, next_ptr);
  } else {
        hp = next_ptr;
  }

  /* If 'hp' now points to the last hole, return; otherwise, try to absorb its
   * successor into it.
   */
  if ( (next_ptr = hp->h_next) == NIL_HOLE) return;
  if (hp->h_base + hp->h_len == next_ptr->h_base) {
        hp->h_len += next_ptr->h_len;
        del_slot(hp, next_ptr);
  }
}

/*===========================================================================*
 *                              mem_init                                     *
 *===========================================================================*/
PUBLIC void mem_init(chunks, free)
struct memory *chunks;          /* list of free memory chunks */
phys_clicks *free;              /* memory size summaries */
{
/* Initialize hole lists.  There are two lists: 'hole_head' points to a linked
 * list of all the holes (unused memory) in the system; 'free_slots' points to
 * a linked list of table entries that are not in use.  Initially, the former
 * list has one entry for each chunk of physical memory, and the second
 * list links together the remaining table slots.  As memory becomes more
 * fragmented in the course of time (i.e., the initial big holes break up into
 * smaller holes), new table slots are needed to represent them.  These slots
 * are taken from the list headed by 'free_slots'.
 */
  int i;
  register struct hole *hp;

  /* Put all holes on the free list. */
  for (hp = &hole[0]; hp < &hole[_NR_HOLES]; hp++) {
        hp->h_next = hp + 1;
        hp->h_base = hp->h_len = 0;
  }
  hole[_NR_HOLES-1].h_next = NIL_HOLE;
  hole_head = NIL_HOLE;
  free_slots = &hole[0];

  /* Use the chunks of physical memory to allocate holes. */
  *free = 0;
  for (i=NR_MEMS-1; i>=0; i--) {
        if (chunks[i].size > 0) {
                free_mem(chunks[i].base, chunks[i].size);
                *free += chunks[i].size;
#if ENABLE_SWAP
                if (swap_base < chunks[i].base + chunks[i].size) 
                        swap_base = chunks[i].base + chunks[i].size;
#endif
        }
  }

#if ENABLE_SWAP
  /* The swap area is represented as a hole above and separate of regular
   * memory.  A hole at the size of the swap file is allocated on "swapon".
   */
  swap_base++;                          /* make separate */
  swap_maxsize = 0 - swap_base;         /* maximum we can possibly use */
#endif
}

/*===========================================================================*
 *                              mem_holes_copy                               *
 *===========================================================================*/
PUBLIC int mem_holes_copy(struct hole *holecopies, size_t *bytes, u32_t *hi)
{
        if(*bytes < sizeof(hole)) return ENOSPC;
        memcpy(holecopies, hole, sizeof(hole));
        *bytes = sizeof(hole);
        *hi = high_watermark;
        return OK;
}

#if ENABLE_SWAP
/*===========================================================================*
 *                              swap_on                                      *
 *===========================================================================*/
PUBLIC int swap_on(file, offset, size)
char *file;                             /* file to swap on */
u32_t offset, size;                     /* area on swap file to use */
{
/* Turn swapping on. */

  if (swap_fd != -1) return(EBUSY);     /* already have swap? */

  tell_fs(CHDIR, who_e, FALSE, 0);      /* be like the caller for open() */
  if ((swap_fd = open(file, O_RDWR)) < 0) return(-errno);
  swap_offset = offset;
  size >>= CLICK_SHIFT;
  if (size > swap_maxsize) size = swap_maxsize;
  if (size > 0) free_mem(swap_base, (phys_clicks) size);
  return(OK);
}

/*===========================================================================*
 *                              swap_off                                     *
 *===========================================================================*/
PUBLIC int swap_off()
{
/* Turn swapping off. */
  struct mproc *rmp;
  struct hole *hp, *prev_ptr;

  if (swap_fd == -1) return(OK);        /* can't turn off what isn't on */

  /* Put all swapped out processes on the inswap queue and swap in. */
  for (rmp = &mproc[0]; rmp < &mproc[NR_PROCS]; rmp++) {
        if (rmp->mp_flags & ONSWAP) swap_inqueue(rmp);
  }
  swap_in();

  /* All in memory? */
  for (rmp = &mproc[0]; rmp < &mproc[NR_PROCS]; rmp++) {
        if (rmp->mp_flags & ONSWAP) return(ENOMEM);
  }

  /* Yes.  Remove the swap hole and close the swap file descriptor. */
  for (hp = hole_head; hp != NIL_HOLE; prev_ptr = hp, hp = hp->h_next) {
        if (hp->h_base >= swap_base) {
                del_slot(prev_ptr, hp);
                hp = hole_head;
        }
  }
  close(swap_fd);
  swap_fd = -1;
  return(OK);
}

/*===========================================================================*
 *                              swap_inqueue                                 *
 *===========================================================================*/
PUBLIC void swap_inqueue(rmp)
register struct mproc *rmp;             /* process to add to the queue */
{
/* Put a swapped out process on the queue of processes to be swapped in.  This
 * happens when such a process gets a signal, or if a reply message must be
 * sent, like when a process doing a wait() has a child that exits.
 */
  struct mproc **pmp;

  if (rmp->mp_flags & SWAPIN) return;   /* already queued */

  
  for (pmp = &in_queue; *pmp != NULL; pmp = &(*pmp)->mp_swapq) {}
  *pmp = rmp;
  rmp->mp_swapq = NULL;
  rmp->mp_flags |= SWAPIN;
}

/*===========================================================================*
 *                              swap_in                                      *
 *===========================================================================*/
PUBLIC void swap_in()
{
/* Try to swap in a process on the inswap queue.  We want to send it a message,
 * interrupt it, or something.
 */
  struct mproc **pmp, *rmp;
  phys_clicks old_base, new_base, size;
  off_t off;
  int proc_nr;

  pmp = &in_queue;
  while ((rmp = *pmp) != NULL) {
        proc_nr = (rmp - mproc);
        size = rmp->mp_seg[S].mem_vir + rmp->mp_seg[S].mem_len
                - rmp->mp_seg[D].mem_vir;

        if (!(rmp->mp_flags & SWAPIN)) {
                /* Guess it got killed.  (Queue is cleaned here.) */
                *pmp = rmp->mp_swapq;
                continue;
        } else
        if ((new_base = alloc_mem(size)) == NO_MEM) {
                /* No memory for this one, try the next. */
                pmp = &rmp->mp_swapq;
        } else {
                /* We've found memory.  Update map and swap in. */
                old_base = rmp->mp_seg[D].mem_phys;
                rmp->mp_seg[D].mem_phys = new_base;
                rmp->mp_seg[S].mem_phys = rmp->mp_seg[D].mem_phys + 
                        (rmp->mp_seg[S].mem_vir - rmp->mp_seg[D].mem_vir);
                sys_newmap(rmp->mp_endpoint, rmp->mp_seg);
                off = swap_offset + ((off_t) (old_base-swap_base)<<CLICK_SHIFT);
                lseek(swap_fd, off, SEEK_SET);
                rw_seg(0, swap_fd, rmp->mp_endpoint, D, (phys_bytes)size << CLICK_SHIFT);
                free_mem(old_base, size);
                rmp->mp_flags &= ~(ONSWAP|SWAPIN);
                *pmp = rmp->mp_swapq;
                check_pending(rmp);     /* a signal may have waked this one */
        }
  }
}

/*===========================================================================*
 *                              swap_out                                     *
 *===========================================================================*/
PRIVATE int swap_out()
{
/* Try to find a process that can be swapped out.  Candidates are those blocked
 * on a system call that PM handles, like wait(), pause() or sigsuspend().
 */
  struct mproc *rmp;
  struct hole *hp, *prev_ptr;
  phys_clicks old_base, new_base, size;
  off_t off;
  int proc_nr;

  rmp = outswap;
  do {
        if (++rmp == &mproc[NR_PROCS]) rmp = &mproc[0];

        /* A candidate? */
        if (!(rmp->mp_flags & (PAUSED | WAITING | SIGSUSPENDED))) continue;

        /* Already on swap or otherwise to be avoided? */
        if (rmp->mp_flags & (DONT_SWAP | TRACED | REPLY | ONSWAP)) continue;

        /* Got one, find a swap hole and swap it out. */
        proc_nr = (rmp - mproc);
        size = rmp->mp_seg[S].mem_vir + rmp->mp_seg[S].mem_len
                - rmp->mp_seg[D].mem_vir;

        prev_ptr = NIL_HOLE;
        for (hp = hole_head; hp != NIL_HOLE; prev_ptr = hp, hp = hp->h_next) {
                if (hp->h_base >= swap_base && hp->h_len >= size) break;
        }
        if (hp == NIL_HOLE) continue;   /* oops, not enough swapspace */
        new_base = hp->h_base;
        hp->h_base += size;
        hp->h_len -= size;
        if (hp->h_len == 0) del_slot(prev_ptr, hp);

        off = swap_offset + ((off_t) (new_base - swap_base) << CLICK_SHIFT);
        lseek(swap_fd, off, SEEK_SET);
        rw_seg(1, swap_fd, rmp->mp_endpoint, D, (phys_bytes)size << CLICK_SHIFT);
        old_base = rmp->mp_seg[D].mem_phys;
        rmp->mp_seg[D].mem_phys = new_base;
        rmp->mp_seg[S].mem_phys = rmp->mp_seg[D].mem_phys + 
                (rmp->mp_seg[S].mem_vir - rmp->mp_seg[D].mem_vir);
        sys_newmap(rmp->mp_endpoint, rmp->mp_seg);
        free_mem(old_base, size);
        rmp->mp_flags |= ONSWAP;

        outswap = rmp;          /* next time start here */
        return(TRUE);
  } while (rmp != outswap);

  return(FALSE);        /* no candidate found */
}
#endif /* SWAP */