429 lines
15 KiB
C
429 lines
15 KiB
C
/* This file is concerned with allocating and freeing arbitrary-size blocks of
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* physical memory on behalf of the FORK and EXEC system calls. The key data
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* structure used is the hole table, which maintains a list of holes in memory.
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* It is kept sorted in order of increasing memory address. The addresses
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* it contains refers to physical memory, starting at absolute address 0
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* (i.e., they are not relative to the start of MM). During system
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* initialization, that part of memory containing the interrupt vectors,
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* kernel, and MM are "allocated" to mark them as not available and to
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* remove them from the hole list.
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*
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* The entry points into this file are:
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* alloc_mem: allocate a given sized chunk of memory
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* free_mem: release a previously allocated chunk of memory
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* mem_init: initialize the tables when MM start up
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* max_hole: returns the largest hole currently available
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*/
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#include "mm.h"
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#include <minix/com.h>
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#include <minix/callnr.h>
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#include <signal.h>
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#include "mproc.h"
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#include "../../kernel/const.h"
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#include "../../kernel/type.h"
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#define NR_HOLES (2*NR_PROCS) /* max # entries in hole table */
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#define NIL_HOLE (struct hole *) 0
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PRIVATE struct hole {
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struct hole *h_next; /* pointer to next entry on the list */
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phys_clicks h_base; /* where does the hole begin? */
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phys_clicks h_len; /* how big is the hole? */
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} hole[NR_HOLES];
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PRIVATE struct hole *hole_head; /* pointer to first hole */
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PRIVATE struct hole *free_slots;/* ptr to list of unused table slots */
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#if ENABLE_SWAP
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PRIVATE int swap_fd = -1; /* file descriptor of open swap file/device */
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PRIVATE u32_t swap_offset; /* offset to start of swap area on swap file */
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PRIVATE phys_clicks swap_base; /* memory offset chosen as swap base */
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PRIVATE phys_clicks swap_maxsize;/* maximum amount of swap "memory" possible */
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PRIVATE struct mproc *in_queue; /* queue of processes wanting to swap in */
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PRIVATE struct mproc *outswap = &mproc[LOW_USER]; /* outswap candidate? */
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#else /* !SWAP */
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#define swap_base ((phys_clicks) -1)
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#endif /* !SWAP */
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FORWARD _PROTOTYPE( void del_slot, (struct hole *prev_ptr, struct hole *hp) );
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FORWARD _PROTOTYPE( void merge, (struct hole *hp) );
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#if ENABLE_SWAP
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FORWARD _PROTOTYPE( int swap_out, (void) );
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#else
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#define swap_out() (0)
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#endif
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/*===========================================================================*
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* alloc_mem *
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*===========================================================================*/
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PUBLIC phys_clicks alloc_mem(clicks)
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phys_clicks clicks; /* amount of memory requested */
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{
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/* Allocate a block of memory from the free list using first fit. The block
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* consists of a sequence of contiguous bytes, whose length in clicks is
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* given by 'clicks'. A pointer to the block is returned. The block is
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* always on a click boundary. This procedure is called when memory is
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* needed for FORK or EXEC. Swap other processes out if needed.
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*/
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register struct hole *hp, *prev_ptr;
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phys_clicks old_base;
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do {
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hp = hole_head;
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while (hp != NIL_HOLE && hp->h_base < swap_base) {
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if (hp->h_len >= clicks) {
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/* We found a hole that is big enough. Use it. */
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old_base = hp->h_base; /* remember where it started */
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hp->h_base += clicks; /* bite a piece off */
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hp->h_len -= clicks; /* ditto */
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/* Delete the hole if used up completely. */
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if (hp->h_len == 0) del_slot(prev_ptr, hp);
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/* Return the start address of the acquired block. */
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return(old_base);
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}
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prev_ptr = hp;
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hp = hp->h_next;
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}
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} while (swap_out()); /* try to swap some other process out */
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return(NO_MEM);
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}
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/*===========================================================================*
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* free_mem *
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*===========================================================================*/
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PUBLIC void free_mem(base, clicks)
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phys_clicks base; /* base address of block to free */
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phys_clicks clicks; /* number of clicks to free */
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{
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/* Return a block of free memory to the hole list. The parameters tell where
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* the block starts in physical memory and how big it is. The block is added
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* to the hole list. If it is contiguous with an existing hole on either end,
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* it is merged with the hole or holes.
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*/
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register struct hole *hp, *new_ptr, *prev_ptr;
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if (clicks == 0) return;
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if ( (new_ptr = free_slots) == NIL_HOLE) panic("Hole table full", NO_NUM);
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new_ptr->h_base = base;
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new_ptr->h_len = clicks;
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free_slots = new_ptr->h_next;
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hp = hole_head;
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/* If this block's address is numerically less than the lowest hole currently
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* available, or if no holes are currently available, put this hole on the
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* front of the hole list.
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*/
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if (hp == NIL_HOLE || base <= hp->h_base) {
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/* Block to be freed goes on front of the hole list. */
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new_ptr->h_next = hp;
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hole_head = new_ptr;
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merge(new_ptr);
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return;
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}
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/* Block to be returned does not go on front of hole list. */
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while (hp != NIL_HOLE && base > hp->h_base) {
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prev_ptr = hp;
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hp = hp->h_next;
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}
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/* We found where it goes. Insert block after 'prev_ptr'. */
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new_ptr->h_next = prev_ptr->h_next;
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prev_ptr->h_next = new_ptr;
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merge(prev_ptr); /* sequence is 'prev_ptr', 'new_ptr', 'hp' */
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}
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/*===========================================================================*
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* del_slot *
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*===========================================================================*/
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PRIVATE void del_slot(prev_ptr, hp)
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register struct hole *prev_ptr; /* pointer to hole entry just ahead of 'hp' */
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register struct hole *hp; /* pointer to hole entry to be removed */
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{
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/* Remove an entry from the hole list. This procedure is called when a
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* request to allocate memory removes a hole in its entirety, thus reducing
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* the numbers of holes in memory, and requiring the elimination of one
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* entry in the hole list.
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*/
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if (hp == hole_head)
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hole_head = hp->h_next;
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else
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prev_ptr->h_next = hp->h_next;
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hp->h_next = free_slots;
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free_slots = hp;
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}
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/*===========================================================================*
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* merge *
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*===========================================================================*/
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PRIVATE void merge(hp)
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register struct hole *hp; /* ptr to hole to merge with its successors */
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{
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/* Check for contiguous holes and merge any found. Contiguous holes can occur
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* when a block of memory is freed, and it happens to abut another hole on
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* either or both ends. The pointer 'hp' points to the first of a series of
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* three holes that can potentially all be merged together.
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*/
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register struct hole *next_ptr;
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/* If 'hp' points to the last hole, no merging is possible. If it does not,
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* try to absorb its successor into it and free the successor's table entry.
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*/
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if ( (next_ptr = hp->h_next) == NIL_HOLE) return;
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if (hp->h_base + hp->h_len == next_ptr->h_base) {
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hp->h_len += next_ptr->h_len; /* first one gets second one's mem */
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del_slot(hp, next_ptr);
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} else {
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hp = next_ptr;
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}
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/* If 'hp' now points to the last hole, return; otherwise, try to absorb its
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* successor into it.
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*/
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if ( (next_ptr = hp->h_next) == NIL_HOLE) return;
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if (hp->h_base + hp->h_len == next_ptr->h_base) {
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hp->h_len += next_ptr->h_len;
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del_slot(hp, next_ptr);
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}
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}
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/*===========================================================================*
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* mem_init *
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*===========================================================================*/
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PUBLIC void mem_init(free)
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phys_clicks *free; /* memory size summaries */
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{
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/* Initialize hole lists. There are two lists: 'hole_head' points to a linked
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* list of all the holes (unused memory) in the system; 'free_slots' points to
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* a linked list of table entries that are not in use. Initially, the former
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* list has one entry for each chunk of physical memory, and the second
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* list links together the remaining table slots. As memory becomes more
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* fragmented in the course of time (i.e., the initial big holes break up into
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* smaller holes), new table slots are needed to represent them. These slots
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* are taken from the list headed by 'free_slots'.
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*/
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struct memory mem[NR_MEMS]; /* chunks of physical memory */
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int i;
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register struct hole *hp;
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phys_clicks base; /* base address of chunk */
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phys_clicks size; /* size of chunk */
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message mess;
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/* Get a copy of the physical memory chunks found at the kernel. */
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if ((i=sys_getmemchunks(mem)) != OK)
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panic("MM couldn't get mem chunks",i);
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/* Put all holes on the free list. */
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for (hp = &hole[0]; hp < &hole[NR_HOLES]; hp++) hp->h_next = hp + 1;
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hole[NR_HOLES-1].h_next = NIL_HOLE;
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hole_head = NIL_HOLE;
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free_slots = &hole[0];
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/* Ask the kernel for chunks of physical memory and allocate holes. */
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*free = 0;
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for (i=0; i<NR_MEMS; i++) {
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if (mem[i].size > 0) {
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free_mem(mem[i].base, mem[i].size);
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*free += mem[i].size;
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#if ENABLE_SWAP
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if (swap_base < mem[i].base + mem[i].size)
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swap_base = mem[i].base+mem[i].size;
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#endif
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}
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}
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#if ENABLE_SWAP
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/* The swap area is represented as a hole above and separate of regular
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* memory. A hole at the size of the swap file is allocated on "swapon".
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*/
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swap_base++; /* make separate */
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swap_maxsize = 0 - swap_base; /* maximum we can possibly use */
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#endif
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}
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#if ENABLE_SWAP
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/*===========================================================================*
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* swap_on *
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*===========================================================================*/
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PUBLIC int swap_on(file, offset, size)
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char *file; /* file to swap on */
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u32_t offset, size; /* area on swap file to use */
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{
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/* Turn swapping on. */
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if (swap_fd != -1) return(EBUSY); /* already have swap? */
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tell_fs(CHDIR, who, FALSE, 0); /* be like the caller for open() */
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if ((swap_fd = open(file, O_RDWR)) < 0) return(-errno);
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swap_offset = offset;
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size >>= CLICK_SHIFT;
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if (size > swap_maxsize) size = swap_maxsize;
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if (size > 0) free_mem(swap_base, (phys_clicks) size);
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}
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/*===========================================================================*
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* swap_off *
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*===========================================================================*/
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PUBLIC int swap_off()
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{
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/* Turn swapping off. */
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struct mproc *rmp;
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struct hole *hp, *prev_ptr;
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if (swap_fd == -1) return(OK); /* can't turn off what isn't on */
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/* Put all swapped out processes on the inswap queue and swap in. */
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for (rmp = &mproc[LOW_USER]; rmp < &mproc[NR_PROCS]; rmp++) {
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if (rmp->mp_flags & ONSWAP) swap_inqueue(rmp);
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}
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swap_in();
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/* All in memory? */
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for (rmp = &mproc[LOW_USER]; rmp < &mproc[NR_PROCS]; rmp++) {
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if (rmp->mp_flags & ONSWAP) return(ENOMEM);
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}
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/* Yes. Remove the swap hole and close the swap file descriptor. */
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for (hp = hole_head; hp != NIL_HOLE; prev_ptr = hp, hp = hp->h_next) {
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if (hp->h_base >= swap_base) {
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del_slot(prev_ptr, hp);
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hp = hole_head;
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}
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}
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close(swap_fd);
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swap_fd = -1;
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return(OK);
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}
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/*===========================================================================*
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* swap_inqueue *
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*===========================================================================*/
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PUBLIC void swap_inqueue(rmp)
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register struct mproc *rmp; /* process to add to the queue */
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{
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/* Put a swapped out process on the queue of processes to be swapped in. This
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* happens when such a process gets a signal, or if a reply message must be
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* sent, like when a process doing a wait() has a child that exits.
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*/
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struct mproc **pmp;
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if (rmp->mp_flags & SWAPIN) return; /* already queued */
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for (pmp = &in_queue; *pmp != NULL; pmp = &(*pmp)->mp_swapq) {}
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*pmp = rmp;
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rmp->mp_swapq = NULL;
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rmp->mp_flags |= SWAPIN;
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}
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/*===========================================================================*
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* swap_in *
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*===========================================================================*/
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PUBLIC void swap_in()
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{
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/* Try to swap in a process on the inswap queue. We want to send it a message,
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* interrupt it, or something.
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*/
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struct mproc **pmp, *rmp;
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phys_clicks old_base, new_base, size;
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off_t off;
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int proc_nr;
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pmp = &in_queue;
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while ((rmp = *pmp) != NULL) {
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proc_nr = (rmp - mproc);
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size = rmp->mp_seg[S].mem_vir + rmp->mp_seg[S].mem_len
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- rmp->mp_seg[D].mem_vir;
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if (!(rmp->mp_flags & SWAPIN)) {
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/* Guess it got killed. (Queue is cleaned here.) */
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*pmp = rmp->mp_swapq;
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continue;
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} else
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if ((new_base = alloc_mem(size)) == NO_MEM) {
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/* No memory for this one, try the next. */
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pmp = &rmp->mp_swapq;
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} else {
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/* We've found memory. Update map and swap in. */
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old_base = rmp->mp_seg[D].mem_phys;
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rmp->mp_seg[D].mem_phys = new_base;
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rmp->mp_seg[S].mem_phys = rmp->mp_seg[D].mem_phys +
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(rmp->mp_seg[S].mem_vir - rmp->mp_seg[D].mem_vir);
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sys_newmap(proc_nr, rmp->mp_seg);
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off = swap_offset + ((off_t) (old_base-swap_base)<<CLICK_SHIFT);
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lseek(swap_fd, off, SEEK_SET);
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rw_seg(0, swap_fd, proc_nr, D, (phys_bytes)size << CLICK_SHIFT);
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free_mem(old_base, size);
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rmp->mp_flags &= ~(ONSWAP|SWAPIN);
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*pmp = rmp->mp_swapq;
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check_pending(rmp); /* a signal may have waked this one */
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}
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}
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}
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/*===========================================================================*
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* swap_out *
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*===========================================================================*/
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PRIVATE int swap_out()
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{
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/* Try to find a process that can be swapped out. Candidates are those blocked
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* on a system call that MM handles, like wait(), pause() or sigsuspend().
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*/
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struct mproc *rmp;
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struct hole *hp, *prev_ptr;
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phys_clicks old_base, new_base, size;
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off_t off;
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int proc_nr;
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rmp = outswap;
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do {
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if (++rmp == &mproc[NR_PROCS]) rmp = &mproc[LOW_USER];
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/* A candidate? */
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if (!(rmp->mp_flags & (PAUSED | WAITING | SIGSUSPENDED))) continue;
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/* Already on swap or otherwise to be avoided? */
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if (rmp->mp_flags & (TRACED | REPLY | ONSWAP)) continue;
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/* Got one, find a swap hole and swap it out. */
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proc_nr = (rmp - mproc);
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size = rmp->mp_seg[S].mem_vir + rmp->mp_seg[S].mem_len
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- rmp->mp_seg[D].mem_vir;
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prev_ptr = NIL_HOLE;
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for (hp = hole_head; hp != NIL_HOLE; prev_ptr = hp, hp = hp->h_next) {
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if (hp->h_base >= swap_base && hp->h_len >= size) break;
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}
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if (hp == NIL_HOLE) continue; /* oops, not enough swapspace */
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new_base = hp->h_base;
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hp->h_base += size;
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hp->h_len -= size;
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if (hp->h_len == 0) del_slot(prev_ptr, hp);
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off = swap_offset + ((off_t) (new_base - swap_base) << CLICK_SHIFT);
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lseek(swap_fd, off, SEEK_SET);
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rw_seg(1, swap_fd, proc_nr, D, (phys_bytes)size << CLICK_SHIFT);
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old_base = rmp->mp_seg[D].mem_phys;
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rmp->mp_seg[D].mem_phys = new_base;
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rmp->mp_seg[S].mem_phys = rmp->mp_seg[D].mem_phys +
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(rmp->mp_seg[S].mem_vir - rmp->mp_seg[D].mem_vir);
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sys_newmap(proc_nr, rmp->mp_seg);
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free_mem(old_base, size);
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rmp->mp_flags |= ONSWAP;
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outswap = rmp; /* next time start here */
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return(TRUE);
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} while (rmp != outswap);
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return(FALSE); /* no candidate found */
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}
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#endif /* SWAP */
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