* better

[mascara-docs.git] / i386 / linux-2.3.21 / mm / vmscan.c

/*
 *  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
 *  Removed kswapd_ctl limits, and swap out as many pages as needed
 *  to bring the system back to freepages.high: 2.4.97, Rik van Riel.
 *  Version: $Id: vmscan.c,v 1.5 1998/02/23 22:14:28 sct Exp $
 */

#include <linux/slab.h>
#include <linux/kernel_stat.h>
#include <linux/swap.h>
#include <linux/swapctl.h>
#include <linux/smp_lock.h>
#include <linux/pagemap.h>
#include <linux/init.h>
#include <linux/bigmem.h>

#include <asm/pgtable.h>

/*
 * 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 int try_to_swap_out(struct vm_area_struct* vma, unsigned long address, pte_t * page_table, int gfp_mask)
{
        pte_t pte;
        unsigned long entry;
        unsigned long page_addr;
        struct page * page;

        pte = *page_table;
        if (!pte_present(pte))
                goto out_failed;
        page_addr = pte_page(pte);
        if (MAP_NR(page_addr) >= max_mapnr)
                goto out_failed;

        page = mem_map + MAP_NR(page_addr);
        spin_lock(&vma->vm_mm->page_table_lock);
        if (pte_val(pte) != pte_val(*page_table))
                goto out_failed_unlock;

        /* Don't look at this pte if it's been accessed recently. */
        if (pte_young(pte)) {
                /*
                 * Transfer the "accessed" bit from the page
                 * tables to the global page map.
                 */
                set_pte(page_table, pte_mkold(pte));
                set_bit(PG_referenced, &page->flags);
                goto out_failed_unlock;
        }

        if (PageReserved(page)
            || PageLocked(page)
            || ((gfp_mask & __GFP_DMA) && !PageDMA(page))
            || (!(gfp_mask & __GFP_BIGMEM) && PageBIGMEM(page)))
                goto out_failed_unlock;

        /*
         * Is the page already in the swap cache? If so, then
         * we can just drop our reference to it without doing
         * any IO - it's already up-to-date on disk.
         *
         * Return 0, as we didn't actually free any real
         * memory, and we should just continue our scan.
         */
        if (PageSwapCache(page)) {
                entry = page->offset;
                swap_duplicate(entry);
                set_pte(page_table, __pte(entry));
drop_pte:
                vma->vm_mm->rss--;
                flush_tlb_page(vma, address);
                __free_page(page);
                goto out_failed_unlock;
        }

        /*
         * Is it a clean page? Then it must be recoverable
         * by just paging it in again, and we can just drop
         * it..
         *
         * However, this won't actually free any real
         * memory, as the page will just be in the page cache
         * somewhere, and as such we should just continue
         * our scan.
         *
         * Basically, this just makes it possible for us to do
         * some real work in the future in "shrink_mmap()".
         */
        if (!pte_dirty(pte)) {
                pte_clear(page_table);
                goto drop_pte;
        }

        /*
         * Don't go down into the swap-out stuff if
         * we cannot do I/O! Avoid recursing on FS
         * locks etc.
         */
        if (!(gfp_mask & __GFP_IO))
                goto out_failed_unlock;

        /*
         * Ok, it's really dirty. That means that
         * we should either create a new swap cache
         * entry for it, or we should write it back
         * to its own backing store.
         *
         * Note that in neither case do we actually
         * know that we make a page available, but
         * as we potentially sleep we can no longer
         * continue scanning, so we migth as well
         * assume we free'd something.
         *
         * NOTE NOTE NOTE! This should just set a
         * dirty bit in 'page', and just drop the
         * pte. All the hard work would be done by
         * shrink_mmap().
         *
         * That would get rid of a lot of problems.
         */
        flush_cache_page(vma, address);
        if (vma->vm_ops && vma->vm_ops->swapout) {
                int error;
                pte_clear(page_table);
                spin_unlock(&vma->vm_mm->page_table_lock);
                flush_tlb_page(vma, address);
                vma->vm_mm->rss--;
                error = vma->vm_ops->swapout(vma, page);
                if (!error)
                        goto out_free_success;
                __free_page(page);
                return error;
        }

        /*
         * This is a dirty, swappable page.  First of all,
         * get a suitable swap entry for it, and make sure
         * we have the swap cache set up to associate the
         * page with that swap entry.
         */
        entry = acquire_swap_entry(page);
        if (!entry)
                goto out_failed_unlock; /* No swap space left */
                
        if (!(page = prepare_bigmem_swapout(page)))
                goto out_swap_free_unlock;

        vma->vm_mm->rss--;
        set_pte(page_table, __pte(entry));
        spin_unlock(&vma->vm_mm->page_table_lock);

        flush_tlb_page(vma, address);
        swap_duplicate(entry);  /* One for the process, one for the swap cache */

        /* This will also lock the page */
        add_to_swap_cache(page, entry);

        /* OK, do a physical asynchronous write to swap.  */
        rw_swap_page(WRITE, page, 0);

out_free_success:
        __free_page(page);
        return 1;
out_failed_unlock:
        spin_unlock(&vma->vm_mm->page_table_lock);
out_failed:
        return 0;
out_swap_free_unlock:
        swap_free(entry);
        spin_unlock(&vma->vm_mm->page_table_lock);
        return 0;

}

/*
 * 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 vm_area_struct * vma, pmd_t *dir, unsigned long address, unsigned long end, int gfp_mask)
{
        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;
                vma->vm_mm->swap_address = address + PAGE_SIZE;
                result = try_to_swap_out(vma, address, pte, gfp_mask);
                if (result)
                        return result;
                address += PAGE_SIZE;
                pte++;
        } while (address < end);
        return 0;
}

static inline int swap_out_pgd(struct vm_area_struct * vma, pgd_t *dir, unsigned long address, unsigned long end, int gfp_mask)
{
        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(vma, pmd, address, end, gfp_mask);
                if (result)
                        return result;
                address = (address + PMD_SIZE) & PMD_MASK;
                pmd++;
        } while (address < end);
        return 0;
}

static int swap_out_vma(struct vm_area_struct * vma, unsigned long address, int gfp_mask)
{
        pgd_t *pgdir;
        unsigned long end;

        /* Don't swap out areas which are locked down */
        if (vma->vm_flags & VM_LOCKED)
                return 0;

        pgdir = pgd_offset(vma->vm_mm, address);

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

static int swap_out_mm(struct mm_struct * mm, int gfp_mask)
{
        unsigned long address;
        struct vm_area_struct* vma;

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

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

                for (;;) {
                        int result = swap_out_vma(vma, address, gfp_mask);
                        if (result)
                                return result;
                        vma = vma->vm_next;
                        if (!vma)
                                break;
                        address = vma->vm_start;
                }
        }

        /* We didn't find anything for the process */
        mm->swap_cnt = 0;
        mm->swap_address = 0;
        return 0;
}

/*
 * Select the task with maximal swap_cnt and try to swap out a page.
 * N.B. This function returns only 0 or 1.  Return values != 1 from
 * the lower level routines result in continued processing.
 */
static int swap_out(unsigned int priority, int gfp_mask)
{
        struct task_struct * p;
        int counter;
        int __ret = 0;

        lock_kernel();
        /* 
         * We make one or two passes through the task list, indexed by 
         * assign = {0, 1}:
         *   Pass 1: select the swappable task with maximal RSS that has
         *         not yet been swapped out. 
         *   Pass 2: re-assign rss swap_cnt values, then select as above.
         *
         * With this approach, there's no need to remember the last task
         * swapped out.  If the swap-out fails, we clear swap_cnt so the 
         * task won't be selected again until all others have been tried.
         *
         * Think of swap_cnt as a "shadow rss" - it tells us which process
         * we want to page out (always try largest first).
         */
        counter = nr_threads / (priority+1);
        if (counter < 1)
                counter = 1;
        if (counter > nr_threads)
                counter = nr_threads;

        for (; counter >= 0; counter--) {
                int assign = 0;
                int max_cnt = 0;
                struct mm_struct *best = NULL;
                int pid = 0;
        select:
                read_lock(&tasklist_lock);
                p = init_task.next_task;
                for (; p != &init_task; p = p->next_task) {
                        struct mm_struct *mm = p->mm;
                        if (!p->swappable || !mm)
                                continue;
                        if (mm->rss <= 0)
                                continue;
                        /* Refresh swap_cnt? */
                        if (assign)
                                mm->swap_cnt = mm->rss;
                        if (mm->swap_cnt > max_cnt) {
                                max_cnt = mm->swap_cnt;
                                best = mm;
                                pid = p->pid;
                        }
                }
                read_unlock(&tasklist_lock);
                if (!best) {
                        if (!assign) {
                                assign = 1;
                                goto select;
                        }
                        goto out;
                } else {
                        int ret;

                        atomic_inc(&best->mm_count);
                        ret = swap_out_mm(best, gfp_mask);
                        mmdrop(best);

                        if (!ret)
                                continue;

                        if (ret < 0)
                                kill_proc(pid, SIGBUS, 1);
                        __ret = 1;
                        goto out;
                }
        }
out:
        unlock_kernel();
        return __ret;
}

/*
 * We need to make the locks finer granularity, but right
 * now we need this so that we can do page allocations
 * without holding the kernel lock etc.
 *
 * We want to try to free "count" pages, and we need to 
 * cluster them so that we get good swap-out behaviour. See
 * the "free_memory()" macro for details.
 */
static int do_try_to_free_pages(unsigned int gfp_mask)
{
        int priority;
        int count = SWAP_CLUSTER_MAX;

        /* Always trim SLAB caches when memory gets low. */
        kmem_cache_reap(gfp_mask);

        priority = 6;
        do {
                while (shrink_mmap(priority, gfp_mask)) {
                        if (!--count)
                                goto done;
                }

                /* don't be too light against the d/i cache since
                   shrink_mmap() almost never fail when there's
                   really plenty of memory free. */
                count -= shrink_dcache_memory(priority, gfp_mask);
                count -= shrink_icache_memory(priority, gfp_mask);
                if (count <= 0)
                        goto done;

                /* Try to get rid of some shared memory pages.. */
                if (gfp_mask & __GFP_IO) {
                        while (shm_swap(priority, gfp_mask)) {
                                if (!--count)
                                        goto done;
                        }
                }

                /* Then, try to page stuff out.. */
                while (swap_out(priority, gfp_mask)) {
                        if (!--count)
                                goto done;
                }
        } while (--priority >= 0);
done:

        return priority >= 0;
}

static struct task_struct *kswapd_process;

/*
 * The background pageout daemon, started as a kernel thread
 * from the init process. 
 *
 * This basically executes once a second, trickling out pages
 * so that we have _some_ free memory available even if there
 * is no other activity that frees anything up. This is needed
 * for things like routing etc, where we otherwise might have
 * all activity going on in asynchronous contexts that cannot
 * page things out.
 *
 * If there are applications that are active memory-allocators
 * (most normal use), this basically shouldn't matter.
 */
int kswapd(void *unused)
{
        struct task_struct *tsk = current;

        kswapd_process = tsk;
        tsk->session = 1;
        tsk->pgrp = 1;
        strcpy(tsk->comm, "kswapd");
        sigfillset(&tsk->blocked);
        
        /*
         * Tell the memory management that we're a "memory allocator",
         * and that if we need more memory we should get access to it
         * regardless (see "__get_free_pages()"). "kswapd" should
         * never get caught in the normal page freeing logic.
         *
         * (Kswapd normally doesn't need memory anyway, but sometimes
         * you need a small amount of memory in order to be able to
         * page out something else, and this flag essentially protects
         * us from recursively trying to free more memory as we're
         * trying to free the first piece of memory in the first place).
         */
        tsk->flags |= PF_MEMALLOC;

        while (1) {
                /*
                 * Wake up once a second to see if we need to make
                 * more memory available.
                 *
                 * If we actually get into a low-memory situation,
                 * the processes needing more memory will wake us
                 * up on a more timely basis.
                 */
                do {
                        /* kswapd is critical to provide GFP_ATOMIC
                           allocations (not GFP_BIGMEM ones). */
                        if (nr_free_pages - nr_free_bigpages >= freepages.high)
                                break;

                        if (!do_try_to_free_pages(GFP_KSWAPD))
                                break;
                        run_task_queue(&tq_disk);
                } while (!tsk->need_resched);
                tsk->state = TASK_INTERRUPTIBLE;
                schedule_timeout(HZ);
        }
}

/*
 * Called by non-kswapd processes when they want more
 * memory.
 *
 * In a perfect world, this should just wake up kswapd
 * and return. We don't actually want to swap stuff out
 * from user processes, because the locking issues are
 * nasty to the extreme (file write locks, and MM locking)
 *
 * One option might be to let kswapd do all the page-out
 * and VM page table scanning that needs locking, and this
 * process thread could do just the mmap shrink stage that
 * can be done by just dropping cached pages without having
 * any deadlock issues.
 */
int try_to_free_pages(unsigned int gfp_mask)
{
        int retval = 1;

        wake_up_process(kswapd_process);
        if (gfp_mask & __GFP_WAIT)
                retval = do_try_to_free_pages(gfp_mask);
        return retval;
}

static int __init kswapd_init(void)
{
        printk("Starting kswapd v1.6\n");
        swap_setup();
        kernel_thread(kswapd, NULL, CLONE_FS | CLONE_FILES | CLONE_SIGHAND);
        return 0;
}

module_init(kswapd_init)