initial version

Book-Lite/linux-0.12/mm/Makefile

@@ -0,0 +1,44 @@
+CC	=gcc
+CFLAGS	=-O -Wall -fstrength-reduce -fcombine-regs -fomit-frame-pointer \
+	-finline-functions -nostdinc -I../include
+AS	=gas
+AR	=gar
+LD	=gld
+CPP	=gcc -E -nostdinc -I../include
+
+.c.o:
+	$(CC) $(CFLAGS) \
+	-c -o $*.o $<
+.s.o:
+	$(AS) -o $*.o $<
+.c.s:
+	$(CC) $(CFLAGS) \
+	-S -o $*.s $<
+
+OBJS	= memory.o swap.o page.o
+
+all: mm.o
+
+mm.o: $(OBJS)
+	$(LD) -r -o mm.o $(OBJS)
+
+clean:
+	rm -f core *.o *.a tmp_make
+	for i in *.c;do rm -f `basename $$i .c`.s;done
+
+dep:
+	sed '/\#\#\# Dependencies/q' < Makefile > tmp_make
+	(for i in *.c;do $(CPP) -M $$i;done) >> tmp_make
+	cp tmp_make Makefile
+
+### Dependencies:
+memory.o : memory.c ../include/signal.h ../include/sys/types.h \
+  ../include/asm/system.h ../include/linux/sched.h ../include/linux/head.h \
+  ../include/linux/fs.h ../include/linux/mm.h ../include/linux/kernel.h \
+  ../include/sys/param.h ../include/sys/time.h ../include/time.h \
+  ../include/sys/resource.h 
+swap.o : swap.c ../include/string.h ../include/linux/sched.h \
+  ../include/linux/head.h ../include/linux/fs.h ../include/sys/types.h \
+  ../include/linux/mm.h ../include/linux/kernel.h ../include/signal.h \
+  ../include/sys/param.h ../include/sys/time.h ../include/time.h \
+  ../include/sys/resource.h 

Book-Lite/linux-0.12/mm/memory.c

@@ -0,0 +1,502 @@
+/*
+ *  linux/mm/memory.c
+ *
+ *  (C) 1991  Linus Torvalds
+ */
+
+/*
+ * demand-loading started 01.12.91 - seems it is high on the list of
+ * things wanted, and it should be easy to implement. - Linus
+ */
+
+/*
+ * Ok, demand-loading was easy, shared pages a little bit tricker. Shared
+ * pages started 02.12.91, seems to work. - Linus.
+ *
+ * Tested sharing by executing about 30 /bin/sh: under the old kernel it
+ * would have taken more than the 6M I have free, but it worked well as
+ * far as I could see.
+ *
+ * Also corrected some "invalidate()"s - I wasn't doing enough of them.
+ */
+
+/*
+ * Real VM (paging to/from disk) started 18.12.91. Much more work and
+ * thought has to go into this. Oh, well..
+ * 19.12.91  -  works, somewhat. Sometimes I get faults, don't know why.
+ *		Found it. Everything seems to work now.
+ * 20.12.91  -  Ok, making the swap-device changeable like the root.
+ */
+
+#include <signal.h>
+
+#include <asm/system.h>
+
+#include <linux/sched.h>
+#include <linux/head.h>
+#include <linux/kernel.h>
+
+#define CODE_SPACE(addr) ((((addr)+4095)&~4095) < \
+current->start_code + current->end_code)
+
+unsigned long HIGH_MEMORY = 0;
+
+#define copy_page(from,to) \
+__asm__("cld ; rep ; movsl"::"S" (from),"D" (to),"c" (1024):"cx","di","si")
+
+unsigned char mem_map [ PAGING_PAGES ] = {0,};
+
+/*
+ * Free a page of memory at physical address 'addr'. Used by
+ * 'free_page_tables()'
+ */
+void free_page(unsigned long addr)
+{
+	if (addr < LOW_MEM) return;
+	if (addr >= HIGH_MEMORY)
+		panic("trying to free nonexistent page");
+	addr -= LOW_MEM;
+	addr >>= 12;
+	if (mem_map[addr]--) return;
+	mem_map[addr]=0;
+	panic("trying to free free page");
+}
+
+/*
+ * This function frees a continuos block of page tables, as needed
+ * by 'exit()'. As does copy_page_tables(), this handles only 4Mb blocks.
+ */
+int free_page_tables(unsigned long from,unsigned long size)
+{
+	unsigned long *pg_table;
+	unsigned long * dir, nr;
+
+	if (from & 0x3fffff)
+		panic("free_page_tables called with wrong alignment");
+	if (!from)
+		panic("Trying to free up swapper memory space");
+	size = (size + 0x3fffff) >> 22;
+	dir = (unsigned long *) ((from>>20) & 0xffc); /* _pg_dir = 0 */
+	for ( ; size-->0 ; dir++) {
+		if (!(1 & *dir))
+			continue;
+		pg_table = (unsigned long *) (0xfffff000 & *dir);
+		for (nr=0 ; nr<1024 ; nr++) {
+			if (*pg_table) {
+				if (1 & *pg_table)
+					free_page(0xfffff000 & *pg_table);
+				else
+					swap_free(*pg_table >> 1);
+				*pg_table = 0;
+			}
+			pg_table++;
+		}
+		free_page(0xfffff000 & *dir);
+		*dir = 0;
+	}
+	invalidate();
+	return 0;
+}
+
+/*
+ *  Well, here is one of the most complicated functions in mm. It
+ * copies a range of linerar addresses by copying only the pages.
+ * Let's hope this is bug-free, 'cause this one I don't want to debug :-)
+ *
+ * Note! We don't copy just any chunks of memory - addresses have to
+ * be divisible by 4Mb (one page-directory entry), as this makes the
+ * function easier. It's used only by fork anyway.
+ *
+ * NOTE 2!! When from==0 we are copying kernel space for the first
+ * fork(). Then we DONT want to copy a full page-directory entry, as
+ * that would lead to some serious memory waste - we just copy the
+ * first 160 pages - 640kB. Even that is more than we need, but it
+ * doesn't take any more memory - we don't copy-on-write in the low
+ * 1 Mb-range, so the pages can be shared with the kernel. Thus the
+ * special case for nr=xxxx.
+ */
+int copy_page_tables(unsigned long from,unsigned long to,long size)
+{
+	unsigned long * from_page_table;
+	unsigned long * to_page_table;
+	unsigned long this_page;
+	unsigned long * from_dir, * to_dir;
+	unsigned long new_page;
+	unsigned long nr;
+
+	if ((from&0x3fffff) || (to&0x3fffff))
+		panic("copy_page_tables called with wrong alignment");
+	from_dir = (unsigned long *) ((from>>20) & 0xffc); /* _pg_dir = 0 */
+	to_dir = (unsigned long *) ((to>>20) & 0xffc);
+	size = ((unsigned) (size+0x3fffff)) >> 22;
+	for( ; size-->0 ; from_dir++,to_dir++) {
+		if (1 & *to_dir)
+			panic("copy_page_tables: already exist");
+		if (!(1 & *from_dir))
+			continue;
+		from_page_table = (unsigned long *) (0xfffff000 & *from_dir);
+		if (!(to_page_table = (unsigned long *) get_free_page()))
+			return -1;	/* Out of memory, see freeing */
+		*to_dir = ((unsigned long) to_page_table) | 7;
+		nr = (from==0)?0xA0:1024;
+		for ( ; nr-- > 0 ; from_page_table++,to_page_table++) {
+			this_page = *from_page_table;
+			if (!this_page)
+				continue;
+			if (!(1 & this_page)) {
+				if (!(new_page = get_free_page()))
+					return -1;
+				read_swap_page(this_page>>1, (char *) new_page);
+				*to_page_table = this_page;
+				*from_page_table = new_page | (PAGE_DIRTY | 7);
+				continue;
+			}
+			this_page &= ~2;
+			*to_page_table = this_page;
+			if (this_page > LOW_MEM) {
+				*from_page_table = this_page;
+				this_page -= LOW_MEM;
+				this_page >>= 12;
+				mem_map[this_page]++;
+			}
+		}
+	}
+	invalidate();
+	return 0;
+}
+
+/*
+ * This function puts a page in memory at the wanted address.
+ * It returns the physical address of the page gotten, 0 if
+ * out of memory (either when trying to access page-table or
+ * page.)
+ */
+static unsigned long put_page(unsigned long page,unsigned long address)
+{
+	unsigned long tmp, *page_table;
+
+/* NOTE !!! This uses the fact that _pg_dir=0 */
+
+	if (page < LOW_MEM || page >= HIGH_MEMORY)
+		printk("Trying to put page %p at %p\n",page,address);
+	if (mem_map[(page-LOW_MEM)>>12] != 1)
+		printk("mem_map disagrees with %p at %p\n",page,address);
+	page_table = (unsigned long *) ((address>>20) & 0xffc);
+	if ((*page_table)&1)
+		page_table = (unsigned long *) (0xfffff000 & *page_table);
+	else {
+		if (!(tmp=get_free_page()))
+			return 0;
+		*page_table = tmp | 7;
+		page_table = (unsigned long *) tmp;
+	}
+	page_table[(address>>12) & 0x3ff] = page | 7;
+/* no need for invalidate */
+	return page;
+}
+
+/*
+ * The previous function doesn't work very well if you also want to mark
+ * the page dirty: exec.c wants this, as it has earlier changed the page,
+ * and we want the dirty-status to be correct (for VM). Thus the same
+ * routine, but this time we mark it dirty too.
+ */
+unsigned long put_dirty_page(unsigned long page, unsigned long address)
+{
+	unsigned long tmp, *page_table;
+
+/* NOTE !!! This uses the fact that _pg_dir=0 */
+
+	if (page < LOW_MEM || page >= HIGH_MEMORY)
+		printk("Trying to put page %p at %p\n",page,address);
+	if (mem_map[(page-LOW_MEM)>>12] != 1)
+		printk("mem_map disagrees with %p at %p\n",page,address);
+	page_table = (unsigned long *) ((address>>20) & 0xffc);
+	if ((*page_table)&1)
+		page_table = (unsigned long *) (0xfffff000 & *page_table);
+	else {
+		if (!(tmp=get_free_page()))
+			return 0;
+		*page_table = tmp|7;
+		page_table = (unsigned long *) tmp;
+	}
+	page_table[(address>>12) & 0x3ff] = page | (PAGE_DIRTY | 7);
+/* no need for invalidate */
+	return page;
+}
+
+void un_wp_page(unsigned long * table_entry)
+{
+	unsigned long old_page,new_page;
+
+	old_page = 0xfffff000 & *table_entry;
+	if (old_page >= LOW_MEM && mem_map[MAP_NR(old_page)]==1) {
+		*table_entry |= 2;
+		invalidate();
+		return;
+	}
+	if (!(new_page=get_free_page()))
+		oom();
+	if (old_page >= LOW_MEM)
+		mem_map[MAP_NR(old_page)]--;
+	copy_page(old_page,new_page);
+	*table_entry = new_page | 7;
+	invalidate();
+}	
+
+/*
+ * This routine handles present pages, when users try to write
+ * to a shared page. It is done by copying the page to a new address
+ * and decrementing the shared-page counter for the old page.
+ *
+ * If it's in code space we exit with a segment error.
+ */
+void do_wp_page(unsigned long error_code,unsigned long address)
+{
+	if (address < TASK_SIZE)
+		printk("\n\rBAD! KERNEL MEMORY WP-ERR!\n\r");
+	if (address - current->start_code > TASK_SIZE) {
+		printk("Bad things happen: page error in do_wp_page\n\r");
+		do_exit(SIGSEGV);
+	}
+#if 0
+/* we cannot do this yet: the estdio library writes to code space */
+/* stupid, stupid. I really want the libc.a from GNU */
+	if (CODE_SPACE(address))
+		do_exit(SIGSEGV);
+#endif
+	un_wp_page((unsigned long *)
+		(((address>>10) & 0xffc) + (0xfffff000 &
+		*((unsigned long *) ((address>>20) &0xffc)))));
+
+}
+
+void write_verify(unsigned long address)
+{
+	unsigned long page;
+
+	if (!( (page = *((unsigned long *) ((address>>20) & 0xffc)) )&1))
+		return;
+	page &= 0xfffff000;
+	page += ((address>>10) & 0xffc);
+	if ((3 & *(unsigned long *) page) == 1)  /* non-writeable, present */
+		un_wp_page((unsigned long *) page);
+	return;
+}
+
+void get_empty_page(unsigned long address)
+{
+	unsigned long tmp;
+
+	if (!(tmp=get_free_page()) || !put_page(tmp,address)) {
+		free_page(tmp);		/* 0 is ok - ignored */
+		oom();
+	}
+}
+
+/*
+ * try_to_share() checks the page at address "address" in the task "p",
+ * to see if it exists, and if it is clean. If so, share it with the current
+ * task.
+ *
+ * NOTE! This assumes we have checked that p != current, and that they
+ * share the same executable or library.
+ */
+static int try_to_share(unsigned long address, struct task_struct * p)
+{
+	unsigned long from;
+	unsigned long to;
+	unsigned long from_page;
+	unsigned long to_page;
+	unsigned long phys_addr;
+
+	from_page = to_page = ((address>>20) & 0xffc);
+	from_page += ((p->start_code>>20) & 0xffc);
+	to_page += ((current->start_code>>20) & 0xffc);
+/* is there a page-directory at from? */
+	from = *(unsigned long *) from_page;
+	if (!(from & 1))
+		return 0;
+	from &= 0xfffff000;
+	from_page = from + ((address>>10) & 0xffc);
+	phys_addr = *(unsigned long *) from_page;
+/* is the page clean and present? */
+	if ((phys_addr & 0x41) != 0x01)
+		return 0;
+	phys_addr &= 0xfffff000;
+	if (phys_addr >= HIGH_MEMORY || phys_addr < LOW_MEM)
+		return 0;
+	to = *(unsigned long *) to_page;
+	if (!(to & 1))
+		if (to = get_free_page())
+			*(unsigned long *) to_page = to | 7;
+		else
+			oom();
+	to &= 0xfffff000;
+	to_page = to + ((address>>10) & 0xffc);
+	if (1 & *(unsigned long *) to_page)
+		panic("try_to_share: to_page already exists");
+/* share them: write-protect */
+	*(unsigned long *) from_page &= ~2;
+	*(unsigned long *) to_page = *(unsigned long *) from_page;
+	invalidate();
+	phys_addr -= LOW_MEM;
+	phys_addr >>= 12;
+	mem_map[phys_addr]++;
+	return 1;
+}
+
+/*
+ * share_page() tries to find a process that could share a page with
+ * the current one. Address is the address of the wanted page relative
+ * to the current data space.
+ *
+ * We first check if it is at all feasible by checking executable->i_count.
+ * It should be >1 if there are other tasks sharing this inode.
+ */
+static int share_page(struct m_inode * inode, unsigned long address)
+{
+	struct task_struct ** p;
+
+	if (inode->i_count < 2 || !inode)
+		return 0;
+	for (p = &LAST_TASK ; p > &FIRST_TASK ; --p) {
+		if (!*p)
+			continue;
+		if (current == *p)
+			continue;
+		if (address < LIBRARY_OFFSET) {
+			if (inode != (*p)->executable)
+				continue;
+		} else {
+			if (inode != (*p)->library)
+				continue;
+		}
+		if (try_to_share(address,*p))
+			return 1;
+	}
+	return 0;
+}
+
+void do_no_page(unsigned long error_code,unsigned long address)
+{
+	int nr[4];
+	unsigned long tmp;
+	unsigned long page;
+	int block,i;
+	struct m_inode * inode;
+
+	if (address < TASK_SIZE)
+		printk("\n\rBAD!! KERNEL PAGE MISSING\n\r");
+	if (address - current->start_code > TASK_SIZE) {
+		printk("Bad things happen: nonexistent page error in do_no_page\n\r");
+		do_exit(SIGSEGV);
+	}
+	page = *(unsigned long *) ((address >> 20) & 0xffc);
+	if (page & 1) {
+		page &= 0xfffff000;
+		page += (address >> 10) & 0xffc;
+		tmp = *(unsigned long *) page;
+		if (tmp && !(1 & tmp)) {
+			swap_in((unsigned long *) page);
+			return;
+		}
+	}
+	address &= 0xfffff000;
+	tmp = address - current->start_code;
+	if (tmp >= LIBRARY_OFFSET ) {
+		inode = current->library;
+		block = 1 + (tmp-LIBRARY_OFFSET) / BLOCK_SIZE;
+	} else if (tmp < current->end_data) {
+		inode = current->executable;
+		block = 1 + tmp / BLOCK_SIZE;
+	} else {
+		inode = NULL;
+		block = 0;
+	}
+	if (!inode) {
+		get_empty_page(address);
+		return;
+	}
+	if (share_page(inode,tmp))
+		return;
+	if (!(page = get_free_page()))
+		oom();
+/* remember that 1 block is used for header */
+	for (i=0 ; i<4 ; block++,i++)
+		nr[i] = bmap(inode,block);
+	bread_page(page,inode->i_dev,nr);
+	i = tmp + 4096 - current->end_data;
+	if (i>4095)
+		i = 0;
+	tmp = page + 4096;
+	while (i-- > 0) {
+		tmp--;
+		*(char *)tmp = 0;
+	}
+	if (put_page(page,address))
+		return;
+	free_page(page);
+	oom();
+}
+
+void mem_init(long start_mem, long end_mem)
+{
+	int i;
+
+	HIGH_MEMORY = end_mem;
+	for (i=0 ; i<PAGING_PAGES ; i++)
+		mem_map[i] = USED;
+	i = MAP_NR(start_mem);
+	end_mem -= start_mem;
+	end_mem >>= 12;
+	while (end_mem-->0)
+		mem_map[i++]=0;
+}
+
+void show_mem(void)
+{
+	int i,j,k,free=0,total=0;
+	int shared=0;
+	unsigned long * pg_tbl;
+
+	printk("Mem-info:\n\r");
+	for(i=0 ; i<PAGING_PAGES ; i++) {
+		if (mem_map[i] == USED)
+			continue;
+		total++;
+		if (!mem_map[i])
+			free++;
+		else
+			shared += mem_map[i]-1;
+	}
+	printk("%d free pages of %d\n\r",free,total);
+	printk("%d pages shared\n\r",shared);
+	k = 0;
+	for(i=4 ; i<1024 ;) {
+		if (1&pg_dir[i]) {
+			if (pg_dir[i]>HIGH_MEMORY) {
+				printk("page directory[%d]: %08X\n\r",
+					i,pg_dir[i]);
+				continue;
+			}
+			if (pg_dir[i]>LOW_MEM)
+				free++,k++;
+			pg_tbl=(unsigned long *) (0xfffff000 & pg_dir[i]);
+			for(j=0 ; j<1024 ; j++)
+				if ((pg_tbl[j]&1) && pg_tbl[j]>LOW_MEM)
+					if (pg_tbl[j]>HIGH_MEMORY)
+						printk("page_dir[%d][%d]: %08X\n\r",
+							i,j, pg_tbl[j]);
+					else
+						k++,free++;
+		}
+		i++;
+		if (!(i&15) && k) {
+			k++,free++;	/* one page/process for task_struct */
+			printk("Process %d: %d pages\n\r",(i>>4)-1,k);
+			k = 0;
+		}
+	}
+	printk("Memory found: %d (%d)\n\r",free-shared,total);
+}

Book-Lite/linux-0.12/mm/page.s

@@ -0,0 +1,40 @@
+/*
+ *  linux/mm/page.s
+ *
+ *  (C) 1991  Linus Torvalds
+ */
+
+/*
+ * page.s contains the low-level page-exception code.
+ * the real work is done in mm.c
+ */
+
+.globl _page_fault
+
+_page_fault:
+	xchgl %eax,(%esp)
+	pushl %ecx
+	pushl %edx
+	push %ds
+	push %es
+	push %fs
+	movl $0x10,%edx
+	mov %dx,%ds
+	mov %dx,%es
+	mov %dx,%fs
+	movl %cr2,%edx
+	pushl %edx
+	pushl %eax
+	testl $1,%eax
+	jne 1f
+	call _do_no_page
+	jmp 2f
+1:	call _do_wp_page
+2:	addl $8,%esp
+	pop %fs
+	pop %es
+	pop %ds
+	popl %edx
+	popl %ecx
+	popl %eax
+	iret

Book-Lite/linux-0.12/mm/swap.c

@@ -0,0 +1,253 @@
+/*
+ *  linux/mm/swap.c
+ *
+ *  (C) 1991  Linus Torvalds
+ */
+
+/*
+ * This file should contain most things doing the swapping from/to disk.
+ * Started 18.12.91
+ */
+
+#include <string.h>
+
+#include <linux/mm.h>
+#include <linux/sched.h>
+#include <linux/head.h>
+#include <linux/kernel.h>
+
+#define SWAP_BITS (4096<<3)
+
+#define bitop(name,op) \
+static inline int name(char * addr,unsigned int nr) \
+{ \
+int __res; \
+__asm__ __volatile__("bt" op " %1,%2; adcl $0,%0" \
+:"=g" (__res) \
+:"r" (nr),"m" (*(addr)),"0" (0)); \
+return __res; \
+}
+
+bitop(bit,"")
+bitop(setbit,"s")
+bitop(clrbit,"r")
+
+static char * swap_bitmap = NULL;
+int SWAP_DEV = 0;
+
+/*
+ * We never page the pages in task[0] - kernel memory.
+ * We page all other pages.
+ */
+#define FIRST_VM_PAGE (TASK_SIZE>>12)
+#define LAST_VM_PAGE (1024*1024)
+#define VM_PAGES (LAST_VM_PAGE - FIRST_VM_PAGE)
+
+static int get_swap_page(void)
+{
+	int nr;
+
+	if (!swap_bitmap)
+		return 0;
+	for (nr = 1; nr < 32768 ; nr++)
+		if (clrbit(swap_bitmap,nr))
+			return nr;
+	return 0;
+}
+
+void swap_free(int swap_nr)
+{
+	if (!swap_nr)
+		return;
+	if (swap_bitmap && swap_nr < SWAP_BITS)
+		if (!setbit(swap_bitmap,swap_nr))
+			return;
+	printk("Swap-space bad (swap_free())\n\r");
+	return;
+}
+
+void swap_in(unsigned long *table_ptr)
+{
+	int swap_nr;
+	unsigned long page;
+
+	if (!swap_bitmap) {
+		printk("Trying to swap in without swap bit-map");
+		return;
+	}
+	if (1 & *table_ptr) {
+		printk("trying to swap in present page\n\r");
+		return;
+	}
+	swap_nr = *table_ptr >> 1;
+	if (!swap_nr) {
+		printk("No swap page in swap_in\n\r");
+		return;
+	}
+	if (!(page = get_free_page()))
+		oom();
+	read_swap_page(swap_nr, (char *) page);
+	if (setbit(swap_bitmap,swap_nr))
+		printk("swapping in multiply from same page\n\r");
+	*table_ptr = page | (PAGE_DIRTY | 7);
+}
+
+int try_to_swap_out(unsigned long * table_ptr)
+{
+	unsigned long page;
+	unsigned long swap_nr;
+
+	page = *table_ptr;
+	if (!(PAGE_PRESENT & page))
+		return 0;
+	if (page - LOW_MEM > PAGING_MEMORY)
+		return 0;
+	if (PAGE_DIRTY & page) {
+		page &= 0xfffff000;
+		if (mem_map[MAP_NR(page)] != 1)
+			return 0;
+		if (!(swap_nr = get_swap_page()))
+			return 0;
+		*table_ptr = swap_nr<<1;
+		invalidate();
+		write_swap_page(swap_nr, (char *) page);
+		free_page(page);
+		return 1;
+	}
+	*table_ptr = 0;
+	invalidate();
+	free_page(page);
+	return 1;
+}
+
+/*
+ * Ok, this has a rather intricate logic - the idea is to make good
+ * and fast machine code. If we didn't worry about that, things would
+ * be easier.
+ */
+int swap_out(void)
+{
+	static int dir_entry = FIRST_VM_PAGE>>10;
+	static int page_entry = -1;
+	int counter = VM_PAGES;
+	int pg_table;
+
+	while (counter>0) {
+		pg_table = pg_dir[dir_entry];
+		if (pg_table & 1)
+			break;
+		counter -= 1024;
+		dir_entry++;
+		if (dir_entry >= 1024)
+			dir_entry = FIRST_VM_PAGE>>10;
+	}
+	pg_table &= 0xfffff000;
+	while (counter-- > 0) {
+		page_entry++;
+		if (page_entry >= 1024) {
+			page_entry = 0;
+		repeat:
+			dir_entry++;
+			if (dir_entry >= 1024)
+				dir_entry = FIRST_VM_PAGE>>10;
+			pg_table = pg_dir[dir_entry];
+			if (!(pg_table&1))
+				if ((counter -= 1024) > 0)
+					goto repeat;
+				else
+					break;
+			pg_table &= 0xfffff000;
+		}
+		if (try_to_swap_out(page_entry + (unsigned long *) pg_table))
+			return 1;
+	}
+	printk("Out of swap-memory\n\r");
+	return 0;
+}
+
+/*
+ * Get physical address of first (actually last :-) free page, and mark it
+ * used. If no free pages left, return 0.
+ */
+unsigned long get_free_page(void)
+{
+register unsigned long __res asm("ax");
+
+repeat:
+	__asm__("std ; repne ; scasb\n\t"
+		"jne 1f\n\t"
+		"movb $1,1(%%edi)\n\t"
+		"sall $12,%%ecx\n\t"
+		"addl %2,%%ecx\n\t"
+		"movl %%ecx,%%edx\n\t"
+		"movl $1024,%%ecx\n\t"
+		"leal 4092(%%edx),%%edi\n\t"
+		"rep ; stosl\n\t"
+		"movl %%edx,%%eax\n"
+		"1:"
+		:"=a" (__res)
+		:"0" (0),"i" (LOW_MEM),"c" (PAGING_PAGES),
+		"D" (mem_map+PAGING_PAGES-1)
+		:"di","cx","dx");
+	if (__res >= HIGH_MEMORY)
+		goto repeat;
+	if (!__res && swap_out())
+		goto repeat;
+	return __res;
+}
+
+void init_swapping(void)
+{
+	extern int *blk_size[];
+	int swap_size,i,j;
+
+	if (!SWAP_DEV)
+		return;
+	if (!blk_size[MAJOR(SWAP_DEV)]) {
+		printk("Unable to get size of swap device\n\r");
+		return;
+	}
+	swap_size = blk_size[MAJOR(SWAP_DEV)][MINOR(SWAP_DEV)];
+	if (!swap_size)
+		return;
+	if (swap_size < 100) {
+		printk("Swap device too small (%d blocks)\n\r",swap_size);
+		return;
+	}
+	swap_size >>= 2;
+	if (swap_size > SWAP_BITS)
+		swap_size = SWAP_BITS;
+	swap_bitmap = (char *) get_free_page();
+	if (!swap_bitmap) {
+		printk("Unable to start swapping: out of memory :-)\n\r");
+		return;
+	}
+	read_swap_page(0,swap_bitmap);
+	if (strncmp("SWAP-SPACE",swap_bitmap+4086,10)) {
+		printk("Unable to find swap-space signature\n\r");
+		free_page((long) swap_bitmap);
+		swap_bitmap = NULL;
+		return;
+	}
+	memset(swap_bitmap+4086,0,10);
+	for (i = 0 ; i < SWAP_BITS ; i++) {
+		if (i == 1)
+			i = swap_size;
+		if (bit(swap_bitmap,i)) {
+			printk("Bad swap-space bit-map\n\r");
+			free_page((long) swap_bitmap);
+			swap_bitmap = NULL;
+			return;
+		}
+	}
+	j = 0;
+	for (i = 1 ; i < swap_size ; i++)
+		if (bit(swap_bitmap,i))
+			j++;
+	if (!j) {
+		free_page((long) swap_bitmap);
+		swap_bitmap = NULL;
+		return;
+	}
+	printk("Swap device ok: %d pages (%d bytes) swap-space\n\r",j,j*4096);
+}