/*
 *  linux/mm/vmscan.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *
 *  Swap reorganised 29.12.95, Stephen Tweedie.
 *  kswapd added: 7.1.96  sct
 *  Version: $Id: vmscan.c,v 1.4.2.2 1996/01/20 18:22:47 linux Exp $
 */

#include <linux/mm.h>
#include <linux/sched.h>
#include <linux/head.h>
#include <linux/kernel.h>
#include <linux/kernel_stat.h>
#include <linux/errno.h>
#include <linux/string.h>
#include <linux/stat.h>
#include <linux/swap.h>
#include <linux/fs.h>
#include <linux/swapctl.h>
#include <linux/pagemap.h>
#include <linux/smp_lock.h>

#include <asm/dma.h>
#include <asm/system.h> /* for cli()/sti() */
#include <asm/segment.h> /* for memcpy_to/fromfs */
#include <asm/bitops.h>
#include <asm/pgtable.h>

/*
 * To check memory consuming code elsewhere set this to 1
 */
#define MM_DEBUG 0

/* 
 * When are we next due for a page scan? 
 */
static int next_swap_jiffies = 0;

/*
 * Was the last kswapd wakeup caused by
 *     nr_free_pages < free_pages_low
 */
static int last_wakeup_low = 0;

/* 
 * How often do we do a pageout scan during normal conditions?
 * Default is four times a second.
 */
int swapout_interval = HZ / 4;

/* 
 * The wait queue for waking up the pageout daemon:
 */
static struct wait_queue * kswapd_wait = NULL;

/* 
 * We avoid doing a reschedule if the pageout daemon is already awake;
 */
static int kswapd_awake = 0;

/*
 * sysctl-modifiable parameters to control the aggressiveness of the
 * page-searching within the kswapd page recovery daemon.
 */
kswapd_control_t kswapd_ctl = {4, -1, -1, -1, -1};

static void init_swap_timer(void);

/*
 * The swap-out functions return 1 if they successfully
 * threw something out, and we got a free page. It returns
 * zero if it couldn't do anything, and any other value
 * indicates it decreased rss, but the page was shared.
 *
 * NOTE! If it sleeps, it *must* return 1 to make sure we
 * don't continue with the swap-out. Otherwise we may be
 * using a process that no longer actually exists (it might
 * have died while we slept).
 */
static inline int try_to_swap_out(struct task_struct * tsk, struct vm_area_struct* vma,
	unsigned long address, pte_t * page_table, int dma, int wait)
{
	pte_t pte;
	unsigned long entry;
	unsigned long page;
	struct page * page_map;

	pte = *page_table;
	if (!pte_present(pte))
		return 0;
	page = pte_page(pte);
	if (MAP_NR(page) >= MAP_NR(high_memory))
		return 0;

	page_map = mem_map + MAP_NR(page);
	if (PageReserved(page_map)
	    || PageLocked(page_map)
	    || (dma && !PageDMA(page_map)))
		return 0;
	/* Deal with page aging.  Pages age from being unused; they
	 * rejuvenate on being accessed.  Only swap old pages (age==0
	 * is oldest). */
	if ((pte_dirty(pte) && delete_from_swap_cache(MAP_NR(page))) 
	    || pte_young(pte))  {
		set_pte(page_table, pte_mkold(pte));
		touch_page(page_map);
		return 0;
	}
	age_page(page_map);
	if (page_map->age)
		return 0;
	if (pte_dirty(pte)) {
		if (vma->vm_ops && vma->vm_ops->swapout) {
			pid_t pid = tsk->pid;
			vma->vm_mm->rss--;
			if (vma->vm_ops->swapout(vma, address - vma->vm_start + vma->vm_offset, page_table))
				kill_proc(pid, SIGBUS, 1);
		} else {
			if (page_map->count != 1)
				return 0;
			if (!(entry = get_swap_page()))
				return 0;
			vma->vm_mm->rss--;
			flush_cache_page(vma, address);
			set_pte(page_table, __pte(entry));
			flush_tlb_page(vma, address);
			tsk->nswap++;
			rw_swap_page(WRITE, entry, (char *) page, wait);
		}
		free_page(page);
		return 1;	/* we slept: the process may not exist any more */
	}
        if ((entry = find_in_swap_cache(MAP_NR(page))))  {
		if (page_map->count != 1) {
			set_pte(page_table, pte_mkdirty(pte));
			printk("Aiee.. duplicated cached swap-cache entry\n");
			return 0;
		}
		vma->vm_mm->rss--;
		flush_cache_page(vma, address);
		set_pte(page_table, __pte(entry));
		flush_tlb_page(vma, address);
		free_page(page);
		return 1;
	} 
	vma->vm_mm->rss--;
	flush_cache_page(vma, address);
	pte_clear(page_table);
	flush_tlb_page(vma, address);
	entry = page_unuse(page);
	free_page(page);
	return entry;
}

/*
 * A new implementation of swap_out().  We do not swap complete processes,
 * but only a small number of blocks, before we continue with the next
 * process.  The number of blocks actually swapped is determined on the
 * number of page faults, that this process actually had in the last time,
 * so we won't swap heavily used processes all the time ...
 *
 * Note: the priority argument is a hint on much CPU to waste with the
 *       swap block search, not a hint, of how much blocks to swap with
 *       each process.
 *
 * (C) 1993 Kai Petzke, wpp@marie.physik.tu-berlin.de
 */

static inline int swap_out_pmd(struct task_struct * tsk, struct vm_area_struct * vma,
	pmd_t *dir, unsigned long address, unsigned long end, int dma, int wait)
{
	pte_t * pte;
	unsigned long pmd_end;

	if (pmd_none(*dir))
		return 0;
	if (pmd_bad(*dir)) {
		printk("swap_out_pmd: bad pmd (%08lx)\n", pmd_val(*dir));
		pmd_clear(dir);
		return 0;
	}
	
	pte = pte_offset(dir, address);
	
	pmd_end = (address + PMD_SIZE) & PMD_MASK;
	if (end > pmd_end)
		end = pmd_end;

	do {
		int result;
		tsk->swap_address = address + PAGE_SIZE;
		result = try_to_swap_out(tsk, vma, address, pte, dma, wait);
		if (result)
			return result;
		address += PAGE_SIZE;
		pte++;
	} while (address < end);
	return 0;
}

static inline int swap_out_pgd(struct task_struct * tsk, struct vm_area_struct * vma,
	pgd_t *dir, unsigned long address, unsigned long end, int dma, int wait)
{
	pmd_t * pmd;
	unsigned long pgd_end;

	if (pgd_none(*dir))
		return 0;
	if (pgd_bad(*dir)) {
		printk("swap_out_pgd: bad pgd (%08lx)\n", pgd_val(*dir));
		pgd_clear(dir);
		return 0;
	}

	pmd = pmd_offset(dir, address);

	pgd_end = (address + PGDIR_SIZE) & PGDIR_MASK;	
	if (end > pgd_end)
		end = pgd_end;
	
	do {
		int result = swap_out_pmd(tsk, vma, pmd, address, end, dma, wait);
		if (result)
			return result;
		address = (address + PMD_SIZE) & PMD_MASK;
		pmd++;
	} while (address < end);
	return 0;
}

static int swap_out_vma(struct task_struct * tsk, struct vm_area_struct * vma,
	pgd_t *pgdir, unsigned long start, int dma, int wait)
{
	unsigned long end;

	/* Don't swap out areas like shared memory which have their
	    own separate swapping mechanism or areas which are locked down */
	if (vma->vm_flags & (VM_SHM | VM_LOCKED))
		return 0;

	end = vma->vm_end;
	while (start < end) {
		int result = swap_out_pgd(tsk, vma, pgdir, start, end, dma, wait);
		if (result)
			return result;
		start = (start + PGDIR_SIZE) & PGDIR_MASK;
		pgdir++;
	}
	return 0;
}

static int swap_out_process(struct task_struct * p, int dma, int wait)
{
	unsigned long address;
	struct vm_area_struct* vma;

	/*
	 * Go through process' page directory.
	 */
	address = p->swap_address;
	p->swap_address = 0;

	/*
	 * Find the proper vm-area
	 */
	vma = find_vma(p->mm, address);
	if (!vma)
		return 0;
	if (address < vma->vm_start)
		address = vma->vm_start;

	for (;;) {
		int result = swap_out_vma(p, vma, pgd_offset(p->mm, address), address, dma, wait);
		if (result)
			return result;
		vma = vma->vm_next;
		if (!vma)
			break;
		address = vma->vm_start;
	}
	p->swap_address = 0;
	return 0;
}

static int swap_out(unsigned int priority, int dma, int wait)
{
	static int swap_task;
	int loop, counter, shfrv;
	struct task_struct *p;

#ifdef MM_DEBUG
	shfrv = 10;
#else
	/*
	 * Trouble due ageing pages: In some situations it is possible that we cross only tasks
	 * which are swapped out or which have only physical pages with age >= 3.
	 * High values of swap_cnt for memory consuming tasks do aggravate such situations.
	 *
	 * If PAGEOUT_WEIGHT has a value of 8192 a right shift value of 10 leads to
	 *     (8 * nr_tasks) >> priority
	 * Together with a high number of tasks, say 100, we have counters (due priority)
	 *     12(6) + 25(5) + 50(4) + 100(3) + 200(2) + 400(1) + 800(0)
	 * and as total result 1587 scans of swap_out() to swap out a task page.
	 *
	 * Just assume 80 tasks are swapped out and the remaining tasks have a swap_cnt value >= 40
	 * together with pages with age >= 3.  Then we need approx 20*40*2 = 1600 scans to get a
	 * free page.
	 * And now assume that the amount of cached pages, buffers, and ipc pages are really low.
	 */
	switch (priority) {
		case 6: case 5: case 4:  /* be friendly */
			shfrv = 10;
			break;
		case 3: case 2: case 1:  /* more intensive */
			shfrv =  9;
			break;
		case 0: default:         /* sorry we need a page */
			shfrv =  8;
			break;
	}
#endif

	counter = ((PAGEOUT_WEIGHT * nr_tasks) >> shfrv) >> priority;
	for(; counter >= 0; counter--) {
		/*
		 * Check that swap_task is suitable for swapping.  If not, look for
		 * the next suitable process.
		 */
		loop = 0;
		while(1) {
			if (swap_task >= NR_TASKS) {
				swap_task = 1;
				if (loop)
					/* all processes are unswappable or already swapped out */
					return 0;
				loop = 1;
			}

			p = task[swap_task];
			if (p && p->swappable && p->mm->rss)
				break;

			swap_task++;
		}

		/*
		 * Determine the number of pages to swap from this process.
		 */
		if (!p->swap_cnt) {
 			/*
			 * Normalise the number of pages swapped by
			 * multiplying by (RSS / 1MB)
			 */
			p->swap_cnt = AGE_CLUSTER_SIZE(p->mm->rss);
		}
		if (!--p->swap_cnt)
			swap_task++;
		switch (swap_out_process(p, dma, wait)) {
			case 0:
				if (p->state == TASK_STOPPED)
					/* Stopped task occupy nonused ram */
					break;
				if (p->swap_cnt)
					swap_task++;
				break;
			case 1:
				return 1;
			default:
				break;
		}
	}
#ifdef MM_DEBUG
	if (!priority) {
		printk("swap_out: physical ram %6dkB, min pages   %6dkB\n",
			(int)(high_memory>>10), min_free_pages<<(PAGE_SHIFT-10));
		printk("swap_out:   free pages %6dkB, async pages %6dkB\n",
			nr_free_pages<<(PAGE_SHIFT-10), nr_async_pages<<(PAGE_SHIFT-10));
	}
#endif
	return 0;
}

/*
 * We are much more aggressive about trying to swap out than we used
 * to be.  This works out OK, because we now do proper aging on page
 * contents. 
 */
int try_to_free_page(int priority, int dma, int wait)
{
	static int state = 0;
	int i=6;
	int stop;

	/* we don't try as hard if we're not waiting.. */
	stop = 3;
	if (wait)
		stop = 0;
	switch (state) {
		do {
		case 0:
			if (shrink_mmap(i, dma))
				return 1;
			state = 1;
		case 1:
			if (shm_swap(i, dma))
				return 1;
			state = 2;
		default:
			if (swap_out(i, dma, wait))
				return 1;
			state = 0;
		i--;
		} while ((i - stop) >= 0);
	}
	return 0;
}

/*
 * Before we start the kernel thread, print out the 
 * kswapd initialization message (otherwise the init message 
 * may be printed in the middle of another driver's init 
 * message).  It looks very bad when that happens.
 */
void kswapd_setup(void)
{
       int i;
       char *revision="$Revision: 1.4.2.2 $", *s, *e;

       if ((s = strchr(revision, ':')) &&
           (e = strchr(s, '$')))
               s++, i = e - s;
       else
               s = revision, i = -1;
       printk ("Starting kswapd v%.*s\n", i, s);
}

/*
 * The background pageout daemon.
 * Started as a kernel thread from the init process.
 */
int kswapd(void *unused)
{
	int i;
	
	current->session = 1;
	current->pgrp = 1;
	sprintf(current->comm, "kswapd");
	current->blocked = ~0UL;
	
	/*
	 *	As a kernel thread we want to tamper with system buffers
	 *	and other internals and thus be subject to the SMP locking
	 *	rules. (On a uniprocessor box this does nothing).
	 */
	 
#ifdef __SMP__
	lock_kernel();
	syscall_count++;
#endif

	/* Give kswapd a realtime priority. */
	current->policy = SCHED_FIFO;
	current->priority = 32;  /* Fixme --- we need to standardise our
				    namings for POSIX.4 realtime scheduling
				    priorities.  */

	init_swap_timer();
	
	while (1) {
		/* low on memory, we need to start swapping soon */
		next_swap_jiffies = jiffies +
			(last_wakeup_low ? swapout_interval >> 1 : swapout_interval);
		kswapd_awake = 0;
		current->signal = 0;
		run_task_queue(&tq_disk);
		interruptible_sleep_on(&kswapd_wait);
		kswapd_awake = 1;
		swapstats.wakeups++;
		/* Do the background pageout: */
		for (i=0; i < kswapd_ctl.maxpages; i++)
			try_to_free_page(GFP_KERNEL, 0,
					 (nr_free_pages < min_free_pages));
	}
}

/* 
 * The swap_tick function gets called on every clock tick.
 */

void swap_tick(void)
{
	int	want_wakeup = 0;

	if ((nr_free_pages + nr_async_pages) < free_pages_low) {
		if (last_wakeup_low)
			want_wakeup = (jiffies >= next_swap_jiffies);
		else
			last_wakeup_low = want_wakeup = 1;
	}
	else if (((nr_free_pages + nr_async_pages) < free_pages_high) && 
	         (jiffies >= next_swap_jiffies)) {
		last_wakeup_low = 0;
		want_wakeup = 1;
	}

	if (want_wakeup) {
		if (!kswapd_awake && kswapd_ctl.maxpages > 0) {
			wake_up(&kswapd_wait);
			need_resched = 1;
		}
	}
	timer_active |= (1<<SWAP_TIMER);
}


/* 
 * Initialise the swap timer
 */

void init_swap_timer(void)
{
	timer_table[SWAP_TIMER].expires = 0;
	timer_table[SWAP_TIMER].fn = swap_tick;
	timer_active |= (1<<SWAP_TIMER);
}