/*
* 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 */
/*
* 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, int can_do_io)
{
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(!can_do_io)
return 0;
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,
int can_do_io)
{
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,
can_do_io);
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,
int can_do_io)
{
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,
can_do_io);
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, int can_do_io)
{
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,
can_do_io);
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, int can_do_io)
{
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,
can_do_io);
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, int can_do_io)
{
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;
}
/*
* kswapd should be more friendly to other processes.
*/
if (kswapd_awake)
shfrv = 10;
#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, can_do_io)) {
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, can_do_io;
/* we don't try as hard if we're not waiting.. */
stop = 3;
can_do_io = 1;
if (wait)
stop = 0;
if (priority == GFP_IO)
can_do_io = 0;
switch (state) {
do {
case 0:
if (shrink_mmap(i, dma, can_do_io))
return 1;
state = 1;
case 1:
if (can_do_io && shm_swap(i, dma))
return 1;
state = 2;
default:
if (swap_out(i, dma, wait, can_do_io))
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, reserved_pages;
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++;
/* Protect our reserved pages: */
i = 0;
reserved_pages = min_free_pages;
if (min_free_pages >= 48)
reserved_pages -= (12 + (reserved_pages>>3));
if (nr_free_pages <= reserved_pages)
i = (1+reserved_pages) - nr_free_pages;
/* Do the background pageout: */
for (i += kswapd_ctl.maxpages; i > 0; 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);
}
