Linux-2.6.12-rc2v2.6.12-rc2

Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.

Let it rip!

1 files changed, 1311 insertions, 0 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
new file mode 100644
index 0000000..4003c05
--- /dev/null
+++ b/mm/vmscan.c
@@ -0,0 +1,1311 @@
+/*
+ *  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.
+ *  Zone aware kswapd started 02/00, Kanoj Sarcar (kanoj@sgi.com).
+ *  Multiqueue VM started 5.8.00, Rik van Riel.
+ */
+
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/kernel_stat.h>
+#include <linux/swap.h>
+#include <linux/pagemap.h>
+#include <linux/init.h>
+#include <linux/highmem.h>
+#include <linux/file.h>
+#include <linux/writeback.h>
+#include <linux/blkdev.h>
+#include <linux/buffer_head.h>	/* for try_to_release_page(),
+					buffer_heads_over_limit */
+#include <linux/mm_inline.h>
+#include <linux/pagevec.h>
+#include <linux/backing-dev.h>
+#include <linux/rmap.h>
+#include <linux/topology.h>
+#include <linux/cpu.h>
+#include <linux/cpuset.h>
+#include <linux/notifier.h>
+#include <linux/rwsem.h>
+
+#include <asm/tlbflush.h>
+#include <asm/div64.h>
+
+#include <linux/swapops.h>
+
+/* possible outcome of pageout() */
+typedef enum {
+	/* failed to write page out, page is locked */
+	PAGE_KEEP,
+	/* move page to the active list, page is locked */
+	PAGE_ACTIVATE,
+	/* page has been sent to the disk successfully, page is unlocked */
+	PAGE_SUCCESS,
+	/* page is clean and locked */
+	PAGE_CLEAN,
+} pageout_t;
+
+struct scan_control {
+	/* Ask refill_inactive_zone, or shrink_cache to scan this many pages */
+	unsigned long nr_to_scan;
+
+	/* Incremented by the number of inactive pages that were scanned */
+	unsigned long nr_scanned;
+
+	/* Incremented by the number of pages reclaimed */
+	unsigned long nr_reclaimed;
+
+	unsigned long nr_mapped;	/* From page_state */
+
+	/* How many pages shrink_cache() should reclaim */
+	int nr_to_reclaim;
+
+	/* Ask shrink_caches, or shrink_zone to scan at this priority */
+	unsigned int priority;
+
+	/* This context's GFP mask */
+	unsigned int gfp_mask;
+
+	int may_writepage;
+
+	/* This context's SWAP_CLUSTER_MAX. If freeing memory for
+	 * suspend, we effectively ignore SWAP_CLUSTER_MAX.
+	 * In this context, it doesn't matter that we scan the
+	 * whole list at once. */
+	int swap_cluster_max;
+};
+
+/*
+ * The list of shrinker callbacks used by to apply pressure to
+ * ageable caches.
+ */
+struct shrinker {
+	shrinker_t		shrinker;
+	struct list_head	list;
+	int			seeks;	/* seeks to recreate an obj */
+	long			nr;	/* objs pending delete */
+};
+
+#define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
+
+#ifdef ARCH_HAS_PREFETCH
+#define prefetch_prev_lru_page(_page, _base, _field)			\
+	do {								\
+		if ((_page)->lru.prev != _base) {			\
+			struct page *prev;				\
+									\
+			prev = lru_to_page(&(_page->lru));		\
+			prefetch(&prev->_field);			\
+		}							\
+	} while (0)
+#else
+#define prefetch_prev_lru_page(_page, _base, _field) do { } while (0)
+#endif
+
+#ifdef ARCH_HAS_PREFETCHW
+#define prefetchw_prev_lru_page(_page, _base, _field)			\
+	do {								\
+		if ((_page)->lru.prev != _base) {			\
+			struct page *prev;				\
+									\
+			prev = lru_to_page(&(_page->lru));		\
+			prefetchw(&prev->_field);			\
+		}							\
+	} while (0)
+#else
+#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
+#endif
+
+/*
+ * From 0 .. 100.  Higher means more swappy.
+ */
+int vm_swappiness = 60;
+static long total_memory;
+
+static LIST_HEAD(shrinker_list);
+static DECLARE_RWSEM(shrinker_rwsem);
+
+/*
+ * Add a shrinker callback to be called from the vm
+ */
+struct shrinker *set_shrinker(int seeks, shrinker_t theshrinker)
+{
+        struct shrinker *shrinker;
+
+        shrinker = kmalloc(sizeof(*shrinker), GFP_KERNEL);
+        if (shrinker) {
+	        shrinker->shrinker = theshrinker;
+	        shrinker->seeks = seeks;
+	        shrinker->nr = 0;
+	        down_write(&shrinker_rwsem);
+	        list_add_tail(&shrinker->list, &shrinker_list);
+	        up_write(&shrinker_rwsem);
+	}
+	return shrinker;
+}
+EXPORT_SYMBOL(set_shrinker);
+
+/*
+ * Remove one
+ */
+void remove_shrinker(struct shrinker *shrinker)
+{
+	down_write(&shrinker_rwsem);
+	list_del(&shrinker->list);
+	up_write(&shrinker_rwsem);
+	kfree(shrinker);
+}
+EXPORT_SYMBOL(remove_shrinker);
+
+#define SHRINK_BATCH 128
+/*
+ * Call the shrink functions to age shrinkable caches
+ *
+ * Here we assume it costs one seek to replace a lru page and that it also
+ * takes a seek to recreate a cache object.  With this in mind we age equal
+ * percentages of the lru and ageable caches.  This should balance the seeks
+ * generated by these structures.
+ *
+ * If the vm encounted mapped pages on the LRU it increase the pressure on
+ * slab to avoid swapping.
+ *
+ * We do weird things to avoid (scanned*seeks*entries) overflowing 32 bits.
+ *
+ * `lru_pages' represents the number of on-LRU pages in all the zones which
+ * are eligible for the caller's allocation attempt.  It is used for balancing
+ * slab reclaim versus page reclaim.
+ */
+static int shrink_slab(unsigned long scanned, unsigned int gfp_mask,
+			unsigned long lru_pages)
+{
+	struct shrinker *shrinker;
+
+	if (scanned == 0)
+		scanned = SWAP_CLUSTER_MAX;
+
+	if (!down_read_trylock(&shrinker_rwsem))
+		return 0;
+
+	list_for_each_entry(shrinker, &shrinker_list, list) {
+		unsigned long long delta;
+		unsigned long total_scan;
+
+		delta = (4 * scanned) / shrinker->seeks;
+		delta *= (*shrinker->shrinker)(0, gfp_mask);
+		do_div(delta, lru_pages + 1);
+		shrinker->nr += delta;
+		if (shrinker->nr < 0)
+			shrinker->nr = LONG_MAX;	/* It wrapped! */
+
+		total_scan = shrinker->nr;
+		shrinker->nr = 0;
+
+		while (total_scan >= SHRINK_BATCH) {
+			long this_scan = SHRINK_BATCH;
+			int shrink_ret;
+
+			shrink_ret = (*shrinker->shrinker)(this_scan, gfp_mask);
+			if (shrink_ret == -1)
+				break;
+			mod_page_state(slabs_scanned, this_scan);
+			total_scan -= this_scan;
+
+			cond_resched();
+		}
+
+		shrinker->nr += total_scan;
+	}
+	up_read(&shrinker_rwsem);
+	return 0;
+}
+
+/* Called without lock on whether page is mapped, so answer is unstable */
+static inline int page_mapping_inuse(struct page *page)
+{
+	struct address_space *mapping;
+
+	/* Page is in somebody's page tables. */
+	if (page_mapped(page))
+		return 1;
+
+	/* Be more reluctant to reclaim swapcache than pagecache */
+	if (PageSwapCache(page))
+		return 1;
+
+	mapping = page_mapping(page);
+	if (!mapping)
+		return 0;
+
+	/* File is mmap'd by somebody? */
+	return mapping_mapped(mapping);
+}
+
+static inline int is_page_cache_freeable(struct page *page)
+{
+	return page_count(page) - !!PagePrivate(page) == 2;
+}
+
+static int may_write_to_queue(struct backing_dev_info *bdi)
+{
+	if (current_is_kswapd())
+		return 1;
+	if (current_is_pdflush())	/* This is unlikely, but why not... */
+		return 1;
+	if (!bdi_write_congested(bdi))
+		return 1;
+	if (bdi == current->backing_dev_info)
+		return 1;
+	return 0;
+}
+
+/*
+ * We detected a synchronous write error writing a page out.  Probably
+ * -ENOSPC.  We need to propagate that into the address_space for a subsequent
+ * fsync(), msync() or close().
+ *
+ * The tricky part is that after writepage we cannot touch the mapping: nothing
+ * prevents it from being freed up.  But we have a ref on the page and once
+ * that page is locked, the mapping is pinned.
+ *
+ * We're allowed to run sleeping lock_page() here because we know the caller has
+ * __GFP_FS.
+ */
+static void handle_write_error(struct address_space *mapping,
+				struct page *page, int error)
+{
+	lock_page(page);
+	if (page_mapping(page) == mapping) {
+		if (error == -ENOSPC)
+			set_bit(AS_ENOSPC, &mapping->flags);
+		else
+			set_bit(AS_EIO, &mapping->flags);
+	}
+	unlock_page(page);
+}
+
+/*
+ * pageout is called by shrink_list() for each dirty page. Calls ->writepage().
+ */
+static pageout_t pageout(struct page *page, struct address_space *mapping)
+{
+	/*
+	 * If the page is dirty, only perform writeback if that write
+	 * will be non-blocking.  To prevent this allocation from being
+	 * stalled by pagecache activity.  But note that there may be
+	 * stalls if we need to run get_block().  We could test
+	 * PagePrivate for that.
+	 *
+	 * If this process is currently in generic_file_write() against
+	 * this page's queue, we can perform writeback even if that
+	 * will block.
+	 *
+	 * If the page is swapcache, write it back even if that would
+	 * block, for some throttling. This happens by accident, because
+	 * swap_backing_dev_info is bust: it doesn't reflect the
+	 * congestion state of the swapdevs.  Easy to fix, if needed.
+	 * See swapfile.c:page_queue_congested().
+	 */
+	if (!is_page_cache_freeable(page))
+		return PAGE_KEEP;
+	if (!mapping) {
+		/*
+		 * Some data journaling orphaned pages can have
+		 * page->mapping == NULL while being dirty with clean buffers.
+		 */
+		if (PageDirty(page) && PagePrivate(page)) {
+			if (try_to_free_buffers(page)) {
+				ClearPageDirty(page);
+				printk("%s: orphaned page\n", __FUNCTION__);
+				return PAGE_CLEAN;
+			}
+		}
+		return PAGE_KEEP;
+	}
+	if (mapping->a_ops->writepage == NULL)
+		return PAGE_ACTIVATE;
+	if (!may_write_to_queue(mapping->backing_dev_info))
+		return PAGE_KEEP;
+
+	if (clear_page_dirty_for_io(page)) {
+		int res;
+		struct writeback_control wbc = {
+			.sync_mode = WB_SYNC_NONE,
+			.nr_to_write = SWAP_CLUSTER_MAX,
+			.nonblocking = 1,
+			.for_reclaim = 1,
+		};
+
+		SetPageReclaim(page);
+		res = mapping->a_ops->writepage(page, &wbc);
+		if (res < 0)
+			handle_write_error(mapping, page, res);
+		if (res == WRITEPAGE_ACTIVATE) {
+			ClearPageReclaim(page);
+			return PAGE_ACTIVATE;
+		}
+		if (!PageWriteback(page)) {
+			/* synchronous write or broken a_ops? */
+			ClearPageReclaim(page);
+		}
+
+		return PAGE_SUCCESS;
+	}
+
+	return PAGE_CLEAN;
+}
+
+/*
+ * shrink_list adds the number of reclaimed pages to sc->nr_reclaimed
+ */
+static int shrink_list(struct list_head *page_list, struct scan_control *sc)
+{
+	LIST_HEAD(ret_pages);
+	struct pagevec freed_pvec;
+	int pgactivate = 0;
+	int reclaimed = 0;
+
+	cond_resched();
+
+	pagevec_init(&freed_pvec, 1);
+	while (!list_empty(page_list)) {
+		struct address_space *mapping;
+		struct page *page;
+		int may_enter_fs;
+		int referenced;
+
+		cond_resched();
+
+		page = lru_to_page(page_list);
+		list_del(&page->lru);
+
+		if (TestSetPageLocked(page))
+			goto keep;
+
+		BUG_ON(PageActive(page));
+
+		sc->nr_scanned++;
+		/* Double the slab pressure for mapped and swapcache pages */
+		if (page_mapped(page) || PageSwapCache(page))
+			sc->nr_scanned++;
+
+		if (PageWriteback(page))
+			goto keep_locked;
+
+		referenced = page_referenced(page, 1, sc->priority <= 0);
+		/* In active use or really unfreeable?  Activate it. */
+		if (referenced && page_mapping_inuse(page))
+			goto activate_locked;
+
+#ifdef CONFIG_SWAP
+		/*
+		 * Anonymous process memory has backing store?
+		 * Try to allocate it some swap space here.
+		 */
+		if (PageAnon(page) && !PageSwapCache(page)) {
+			if (!add_to_swap(page))
+				goto activate_locked;
+		}
+#endif /* CONFIG_SWAP */
+
+		mapping = page_mapping(page);
+		may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
+			(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
+
+		/*
+		 * The page is mapped into the page tables of one or more
+		 * processes. Try to unmap it here.
+		 */
+		if (page_mapped(page) && mapping) {
+			switch (try_to_unmap(page)) {
+			case SWAP_FAIL:
+				goto activate_locked;
+			case SWAP_AGAIN:
+				goto keep_locked;
+			case SWAP_SUCCESS:
+				; /* try to free the page below */
+			}
+		}
+
+		if (PageDirty(page)) {
+			if (referenced)
+				goto keep_locked;
+			if (!may_enter_fs)
+				goto keep_locked;
+			if (laptop_mode && !sc->may_writepage)
+				goto keep_locked;
+
+			/* Page is dirty, try to write it out here */
+			switch(pageout(page, mapping)) {
+			case PAGE_KEEP:
+				goto keep_locked;
+			case PAGE_ACTIVATE:
+				goto activate_locked;
+			case PAGE_SUCCESS:
+				if (PageWriteback(page) || PageDirty(page))
+					goto keep;
+				/*
+				 * A synchronous write - probably a ramdisk.  Go
+				 * ahead and try to reclaim the page.
+				 */
+				if (TestSetPageLocked(page))
+					goto keep;
+				if (PageDirty(page) || PageWriteback(page))
+					goto keep_locked;
+				mapping = page_mapping(page);
+			case PAGE_CLEAN:
+				; /* try to free the page below */
+			}
+		}
+
+		/*
+		 * If the page has buffers, try to free the buffer mappings
+		 * associated with this page. If we succeed we try to free
+		 * the page as well.
+		 *
+		 * We do this even if the page is PageDirty().
+		 * try_to_release_page() does not perform I/O, but it is
+		 * possible for a page to have PageDirty set, but it is actually
+		 * clean (all its buffers are clean).  This happens if the
+		 * buffers were written out directly, with submit_bh(). ext3
+		 * will do this, as well as the blockdev mapping. 
+		 * try_to_release_page() will discover that cleanness and will
+		 * drop the buffers and mark the page clean - it can be freed.
+		 *
+		 * Rarely, pages can have buffers and no ->mapping.  These are
+		 * the pages which were not successfully invalidated in
+		 * truncate_complete_page().  We try to drop those buffers here
+		 * and if that worked, and the page is no longer mapped into
+		 * process address space (page_count == 1) it can be freed.
+		 * Otherwise, leave the page on the LRU so it is swappable.
+		 */
+		if (PagePrivate(page)) {
+			if (!try_to_release_page(page, sc->gfp_mask))
+				goto activate_locked;
+			if (!mapping && page_count(page) == 1)
+				goto free_it;
+		}
+
+		if (!mapping)
+			goto keep_locked;	/* truncate got there first */
+
+		write_lock_irq(&mapping->tree_lock);
+
+		/*
+		 * The non-racy check for busy page.  It is critical to check
+		 * PageDirty _after_ making sure that the page is freeable and
+		 * not in use by anybody. 	(pagecache + us == 2)
+		 */
+		if (page_count(page) != 2 || PageDirty(page)) {
+			write_unlock_irq(&mapping->tree_lock);
+			goto keep_locked;
+		}
+
+#ifdef CONFIG_SWAP
+		if (PageSwapCache(page)) {
+			swp_entry_t swap = { .val = page->private };
+			__delete_from_swap_cache(page);
+			write_unlock_irq(&mapping->tree_lock);
+			swap_free(swap);
+			__put_page(page);	/* The pagecache ref */
+			goto free_it;
+		}
+#endif /* CONFIG_SWAP */
+
+		__remove_from_page_cache(page);
+		write_unlock_irq(&mapping->tree_lock);
+		__put_page(page);
+
+free_it:
+		unlock_page(page);
+		reclaimed++;
+		if (!pagevec_add(&freed_pvec, page))
+			__pagevec_release_nonlru(&freed_pvec);
+		continue;
+
+activate_locked:
+		SetPageActive(page);
+		pgactivate++;
+keep_locked:
+		unlock_page(page);
+keep:
+		list_add(&page->lru, &ret_pages);
+		BUG_ON(PageLRU(page));
+	}
+	list_splice(&ret_pages, page_list);
+	if (pagevec_count(&freed_pvec))
+		__pagevec_release_nonlru(&freed_pvec);
+	mod_page_state(pgactivate, pgactivate);
+	sc->nr_reclaimed += reclaimed;
+	return reclaimed;
+}
+
+/*
+ * zone->lru_lock is heavily contended.  Some of the functions that
+ * shrink the lists perform better by taking out a batch of pages
+ * and working on them outside the LRU lock.
+ *
+ * For pagecache intensive workloads, this function is the hottest
+ * spot in the kernel (apart from copy_*_user functions).
+ *
+ * Appropriate locks must be held before calling this function.
+ *
+ * @nr_to_scan:	The number of pages to look through on the list.
+ * @src:	The LRU list to pull pages off.
+ * @dst:	The temp list to put pages on to.
+ * @scanned:	The number of pages that were scanned.
+ *
+ * returns how many pages were moved onto *@dst.
+ */
+static int isolate_lru_pages(int nr_to_scan, struct list_head *src,
+			     struct list_head *dst, int *scanned)
+{
+	int nr_taken = 0;
+	struct page *page;
+	int scan = 0;
+
+	while (scan++ < nr_to_scan && !list_empty(src)) {
+		page = lru_to_page(src);
+		prefetchw_prev_lru_page(page, src, flags);
+
+		if (!TestClearPageLRU(page))
+			BUG();
+		list_del(&page->lru);
+		if (get_page_testone(page)) {
+			/*
+			 * It is being freed elsewhere
+			 */
+			__put_page(page);
+			SetPageLRU(page);
+			list_add(&page->lru, src);
+			continue;
+		} else {
+			list_add(&page->lru, dst);
+			nr_taken++;
+		}
+	}
+
+	*scanned = scan;
+	return nr_taken;
+}
+
+/*
+ * shrink_cache() adds the number of pages reclaimed to sc->nr_reclaimed
+ */
+static void shrink_cache(struct zone *zone, struct scan_control *sc)
+{
+	LIST_HEAD(page_list);
+	struct pagevec pvec;
+	int max_scan = sc->nr_to_scan;
+
+	pagevec_init(&pvec, 1);
+
+	lru_add_drain();
+	spin_lock_irq(&zone->lru_lock);
+	while (max_scan > 0) {
+		struct page *page;
+		int nr_taken;
+		int nr_scan;
+		int nr_freed;
+
+		nr_taken = isolate_lru_pages(sc->swap_cluster_max,
+					     &zone->inactive_list,
+					     &page_list, &nr_scan);
+		zone->nr_inactive -= nr_taken;
+		zone->pages_scanned += nr_scan;
+		spin_unlock_irq(&zone->lru_lock);
+
+		if (nr_taken == 0)
+			goto done;
+
+		max_scan -= nr_scan;
+		if (current_is_kswapd())
+			mod_page_state_zone(zone, pgscan_kswapd, nr_scan);
+		else
+			mod_page_state_zone(zone, pgscan_direct, nr_scan);
+		nr_freed = shrink_list(&page_list, sc);
+		if (current_is_kswapd())
+			mod_page_state(kswapd_steal, nr_freed);
+		mod_page_state_zone(zone, pgsteal, nr_freed);
+		sc->nr_to_reclaim -= nr_freed;
+
+		spin_lock_irq(&zone->lru_lock);
+		/*
+		 * Put back any unfreeable pages.
+		 */
+		while (!list_empty(&page_list)) {
+			page = lru_to_page(&page_list);
+			if (TestSetPageLRU(page))
+				BUG();
+			list_del(&page->lru);
+			if (PageActive(page))
+				add_page_to_active_list(zone, page);
+			else
+				add_page_to_inactive_list(zone, page);
+			if (!pagevec_add(&pvec, page)) {
+				spin_unlock_irq(&zone->lru_lock);
+				__pagevec_release(&pvec);
+				spin_lock_irq(&zone->lru_lock);
+			}
+		}
+  	}
+	spin_unlock_irq(&zone->lru_lock);
+done:
+	pagevec_release(&pvec);
+}
+
+/*
+ * This moves pages from the active list to the inactive list.
+ *
+ * We move them the other way if the page is referenced by one or more
+ * processes, from rmap.
+ *
+ * If the pages are mostly unmapped, the processing is fast and it is
+ * appropriate to hold zone->lru_lock across the whole operation.  But if
+ * the pages are mapped, the processing is slow (page_referenced()) so we
+ * should drop zone->lru_lock around each page.  It's impossible to balance
+ * this, so instead we remove the pages from the LRU while processing them.
+ * It is safe to rely on PG_active against the non-LRU pages in here because
+ * nobody will play with that bit on a non-LRU page.
+ *
+ * The downside is that we have to touch page->_count against each page.
+ * But we had to alter page->flags anyway.
+ */
+static void
+refill_inactive_zone(struct zone *zone, struct scan_control *sc)
+{
+	int pgmoved;
+	int pgdeactivate = 0;
+	int pgscanned;
+	int nr_pages = sc->nr_to_scan;
+	LIST_HEAD(l_hold);	/* The pages which were snipped off */
+	LIST_HEAD(l_inactive);	/* Pages to go onto the inactive_list */
+	LIST_HEAD(l_active);	/* Pages to go onto the active_list */
+	struct page *page;
+	struct pagevec pvec;
+	int reclaim_mapped = 0;
+	long mapped_ratio;
+	long distress;
+	long swap_tendency;
+
+	lru_add_drain();
+	spin_lock_irq(&zone->lru_lock);
+	pgmoved = isolate_lru_pages(nr_pages, &zone->active_list,
+				    &l_hold, &pgscanned);
+	zone->pages_scanned += pgscanned;
+	zone->nr_active -= pgmoved;
+	spin_unlock_irq(&zone->lru_lock);
+
+	/*
+	 * `distress' is a measure of how much trouble we're having reclaiming
+	 * pages.  0 -> no problems.  100 -> great trouble.
+	 */
+	distress = 100 >> zone->prev_priority;
+
+	/*
+	 * The point of this algorithm is to decide when to start reclaiming
+	 * mapped memory instead of just pagecache.  Work out how much memory
+	 * is mapped.
+	 */
+	mapped_ratio = (sc->nr_mapped * 100) / total_memory;
+
+	/*
+	 * Now decide how much we really want to unmap some pages.  The mapped
+	 * ratio is downgraded - just because there's a lot of mapped memory
+	 * doesn't necessarily mean that page reclaim isn't succeeding.
+	 *
+	 * The distress ratio is important - we don't want to start going oom.
+	 *
+	 * A 100% value of vm_swappiness overrides this algorithm altogether.
+	 */
+	swap_tendency = mapped_ratio / 2 + distress + vm_swappiness;
+
+	/*
+	 * Now use this metric to decide whether to start moving mapped memory
+	 * onto the inactive list.
+	 */
+	if (swap_tendency >= 100)
+		reclaim_mapped = 1;
+
+	while (!list_empty(&l_hold)) {
+		cond_resched();
+		page = lru_to_page(&l_hold);
+		list_del(&page->lru);
+		if (page_mapped(page)) {
+			if (!reclaim_mapped ||
+			    (total_swap_pages == 0 && PageAnon(page)) ||
+			    page_referenced(page, 0, sc->priority <= 0)) {
+				list_add(&page->lru, &l_active);
+				continue;
+			}
+		}
+		list_add(&page->lru, &l_inactive);
+	}
+
+	pagevec_init(&pvec, 1);
+	pgmoved = 0;
+	spin_lock_irq(&zone->lru_lock);
+	while (!list_empty(&l_inactive)) {
+		page = lru_to_page(&l_inactive);
+		prefetchw_prev_lru_page(page, &l_inactive, flags);
+		if (TestSetPageLRU(page))
+			BUG();
+		if (!TestClearPageActive(page))
+			BUG();
+		list_move(&page->lru, &zone->inactive_list);
+		pgmoved++;
+		if (!pagevec_add(&pvec, page)) {
+			zone->nr_inactive += pgmoved;
+			spin_unlock_irq(&zone->lru_lock);
+			pgdeactivate += pgmoved;
+			pgmoved = 0;
+			if (buffer_heads_over_limit)
+				pagevec_strip(&pvec);
+			__pagevec_release(&pvec);
+			spin_lock_irq(&zone->lru_lock);
+		}
+	}
+	zone->nr_inactive += pgmoved;
+	pgdeactivate += pgmoved;
+	if (buffer_heads_over_limit) {
+		spin_unlock_irq(&zone->lru_lock);
+		pagevec_strip(&pvec);
+		spin_lock_irq(&zone->lru_lock);
+	}
+
+	pgmoved = 0;
+	while (!list_empty(&l_active)) {
+		page = lru_to_page(&l_active);
+		prefetchw_prev_lru_page(page, &l_active, flags);
+		if (TestSetPageLRU(page))
+			BUG();
+		BUG_ON(!PageActive(page));
+		list_move(&page->lru, &zone->active_list);
+		pgmoved++;
+		if (!pagevec_add(&pvec, page)) {
+			zone->nr_active += pgmoved;
+			pgmoved = 0;
+			spin_unlock_irq(&zone->lru_lock);
+			__pagevec_release(&pvec);
+			spin_lock_irq(&zone->lru_lock);
+		}
+	}
+	zone->nr_active += pgmoved;
+	spin_unlock_irq(&zone->lru_lock);
+	pagevec_release(&pvec);
+
+	mod_page_state_zone(zone, pgrefill, pgscanned);
+	mod_page_state(pgdeactivate, pgdeactivate);
+}
+
+/*
+ * This is a basic per-zone page freer.  Used by both kswapd and direct reclaim.
+ */
+static void
+shrink_zone(struct zone *zone, struct scan_control *sc)
+{
+	unsigned long nr_active;
+	unsigned long nr_inactive;
+
+	/*
+	 * Add one to `nr_to_scan' just to make sure that the kernel will
+	 * slowly sift through the active list.
+	 */
+	zone->nr_scan_active += (zone->nr_active >> sc->priority) + 1;
+	nr_active = zone->nr_scan_active;
+	if (nr_active >= sc->swap_cluster_max)
+		zone->nr_scan_active = 0;
+	else
+		nr_active = 0;
+
+	zone->nr_scan_inactive += (zone->nr_inactive >> sc->priority) + 1;
+	nr_inactive = zone->nr_scan_inactive;
+	if (nr_inactive >= sc->swap_cluster_max)
+		zone->nr_scan_inactive = 0;
+	else
+		nr_inactive = 0;
+
+	sc->nr_to_reclaim = sc->swap_cluster_max;
+
+	while (nr_active || nr_inactive) {
+		if (nr_active) {
+			sc->nr_to_scan = min(nr_active,
+					(unsigned long)sc->swap_cluster_max);
+			nr_active -= sc->nr_to_scan;
+			refill_inactive_zone(zone, sc);
+		}
+
+		if (nr_inactive) {
+			sc->nr_to_scan = min(nr_inactive,
+					(unsigned long)sc->swap_cluster_max);
+			nr_inactive -= sc->nr_to_scan;
+			shrink_cache(zone, sc);
+			if (sc->nr_to_reclaim <= 0)
+				break;
+		}
+	}
+
+	throttle_vm_writeout();
+}
+
+/*
+ * This is the direct reclaim path, for page-allocating processes.  We only
+ * try to reclaim pages from zones which will satisfy the caller's allocation
+ * request.
+ *
+ * We reclaim from a zone even if that zone is over pages_high.  Because:
+ * a) The caller may be trying to free *extra* pages to satisfy a higher-order
+ *    allocation or
+ * b) The zones may be over pages_high but they must go *over* pages_high to
+ *    satisfy the `incremental min' zone defense algorithm.
+ *
+ * Returns the number of reclaimed pages.
+ *
+ * If a zone is deemed to be full of pinned pages then just give it a light
+ * scan then give up on it.
+ */
+static void
+shrink_caches(struct zone **zones, struct scan_control *sc)
+{
+	int i;
+
+	for (i = 0; zones[i] != NULL; i++) {
+		struct zone *zone = zones[i];
+
+		if (zone->present_pages == 0)
+			continue;
+
+		if (!cpuset_zone_allowed(zone))
+			continue;
+
+		zone->temp_priority = sc->priority;
+		if (zone->prev_priority > sc->priority)
+			zone->prev_priority = sc->priority;
+
+		if (zone->all_unreclaimable && sc->priority != DEF_PRIORITY)
+			continue;	/* Let kswapd poll it */
+
+		shrink_zone(zone, sc);
+	}
+}
+ 
+/*
+ * This is the main entry point to direct page reclaim.
+ *
+ * If a full scan of the inactive list fails to free enough memory then we
+ * are "out of memory" and something needs to be killed.
+ *
+ * If the caller is !__GFP_FS then the probability of a failure is reasonably
+ * high - the zone may be full of dirty or under-writeback pages, which this
+ * caller can't do much about.  We kick pdflush and take explicit naps in the
+ * hope that some of these pages can be written.  But if the allocating task
+ * holds filesystem locks which prevent writeout this might not work, and the
+ * allocation attempt will fail.
+ */
+int try_to_free_pages(struct zone **zones,
+		unsigned int gfp_mask, unsigned int order)
+{
+	int priority;
+	int ret = 0;
+	int total_scanned = 0, total_reclaimed = 0;
+	struct reclaim_state *reclaim_state = current->reclaim_state;
+	struct scan_control sc;
+	unsigned long lru_pages = 0;
+	int i;
+
+	sc.gfp_mask = gfp_mask;
+	sc.may_writepage = 0;
+
+	inc_page_state(allocstall);
+
+	for (i = 0; zones[i] != NULL; i++) {
+		struct zone *zone = zones[i];
+
+		if (!cpuset_zone_allowed(zone))
+			continue;
+
+		zone->temp_priority = DEF_PRIORITY;
+		lru_pages += zone->nr_active + zone->nr_inactive;
+	}
+
+	for (priority = DEF_PRIORITY; priority >= 0; priority--) {
+		sc.nr_mapped = read_page_state(nr_mapped);
+		sc.nr_scanned = 0;
+		sc.nr_reclaimed = 0;
+		sc.priority = priority;
+		sc.swap_cluster_max = SWAP_CLUSTER_MAX;
+		shrink_caches(zones, &sc);
+		shrink_slab(sc.nr_scanned, gfp_mask, lru_pages);
+		if (reclaim_state) {
+			sc.nr_reclaimed += reclaim_state->reclaimed_slab;
+			reclaim_state->reclaimed_slab = 0;
+		}
+		total_scanned += sc.nr_scanned;
+		total_reclaimed += sc.nr_reclaimed;
+		if (total_reclaimed >= sc.swap_cluster_max) {
+			ret = 1;
+			goto out;
+		}
+
+		/*
+		 * Try to write back as many pages as we just scanned.  This
+		 * tends to cause slow streaming writers to write data to the
+		 * disk smoothly, at the dirtying rate, which is nice.   But
+		 * that's undesirable in laptop mode, where we *want* lumpy
+		 * writeout.  So in laptop mode, write out the whole world.
+		 */
+		if (total_scanned > sc.swap_cluster_max + sc.swap_cluster_max/2) {
+			wakeup_bdflush(laptop_mode ? 0 : total_scanned);
+			sc.may_writepage = 1;
+		}
+
+		/* Take a nap, wait for some writeback to complete */
+		if (sc.nr_scanned && priority < DEF_PRIORITY - 2)
+			blk_congestion_wait(WRITE, HZ/10);
+	}
+out:
+	for (i = 0; zones[i] != 0; i++) {
+		struct zone *zone = zones[i];
+
+		if (!cpuset_zone_allowed(zone))
+			continue;
+
+		zone->prev_priority = zone->temp_priority;
+	}
+	return ret;
+}
+
+/*
+ * For kswapd, balance_pgdat() will work across all this node's zones until
+ * they are all at pages_high.
+ *
+ * If `nr_pages' is non-zero then it is the number of pages which are to be
+ * reclaimed, regardless of the zone occupancies.  This is a software suspend
+ * special.
+ *
+ * Returns the number of pages which were actually freed.
+ *
+ * There is special handling here for zones which are full of pinned pages.
+ * This can happen if the pages are all mlocked, or if they are all used by
+ * device drivers (say, ZONE_DMA).  Or if they are all in use by hugetlb.
+ * What we do is to detect the case where all pages in the zone have been
+ * scanned twice and there has been zero successful reclaim.  Mark the zone as
+ * dead and from now on, only perform a short scan.  Basically we're polling
+ * the zone for when the problem goes away.
+ *
+ * kswapd scans the zones in the highmem->normal->dma direction.  It skips
+ * zones which have free_pages > pages_high, but once a zone is found to have
+ * free_pages <= pages_high, we scan that zone and the lower zones regardless
+ * of the number of free pages in the lower zones.  This interoperates with
+ * the page allocator fallback scheme to ensure that aging of pages is balanced
+ * across the zones.
+ */
+static int balance_pgdat(pg_data_t *pgdat, int nr_pages, int order)
+{
+	int to_free = nr_pages;
+	int all_zones_ok;
+	int priority;
+	int i;
+	int total_scanned, total_reclaimed;
+	struct reclaim_state *reclaim_state = current->reclaim_state;
+	struct scan_control sc;
+
+loop_again:
+	total_scanned = 0;
+	total_reclaimed = 0;
+	sc.gfp_mask = GFP_KERNEL;
+	sc.may_writepage = 0;
+	sc.nr_mapped = read_page_state(nr_mapped);
+
+	inc_page_state(pageoutrun);
+
+	for (i = 0; i < pgdat->nr_zones; i++) {
+		struct zone *zone = pgdat->node_zones + i;
+
+		zone->temp_priority = DEF_PRIORITY;
+	}
+
+	for (priority = DEF_PRIORITY; priority >= 0; priority--) {
+		int end_zone = 0;	/* Inclusive.  0 = ZONE_DMA */
+		unsigned long lru_pages = 0;
+
+		all_zones_ok = 1;
+
+		if (nr_pages == 0) {
+			/*
+			 * Scan in the highmem->dma direction for the highest
+			 * zone which needs scanning
+			 */
+			for (i = pgdat->nr_zones - 1; i >= 0; i--) {
+				struct zone *zone = pgdat->node_zones + i;
+
+				if (zone->present_pages == 0)
+					continue;
+
+				if (zone->all_unreclaimable &&
+						priority != DEF_PRIORITY)
+					continue;
+
+				if (!zone_watermark_ok(zone, order,
+						zone->pages_high, 0, 0, 0)) {
+					end_zone = i;
+					goto scan;
+				}
+			}
+			goto out;
+		} else {
+			end_zone = pgdat->nr_zones - 1;
+		}
+scan:
+		for (i = 0; i <= end_zone; i++) {
+			struct zone *zone = pgdat->node_zones + i;
+
+			lru_pages += zone->nr_active + zone->nr_inactive;
+		}
+
+		/*
+		 * Now scan the zone in the dma->highmem direction, stopping
+		 * at the last zone which needs scanning.
+		 *
+		 * We do this because the page allocator works in the opposite
+		 * direction.  This prevents the page allocator from allocating
+		 * pages behind kswapd's direction of progress, which would
+		 * cause too much scanning of the lower zones.
+		 */
+		for (i = 0; i <= end_zone; i++) {
+			struct zone *zone = pgdat->node_zones + i;
+
+			if (zone->present_pages == 0)
+				continue;
+
+			if (zone->all_unreclaimable && priority != DEF_PRIORITY)
+				continue;
+
+			if (nr_pages == 0) {	/* Not software suspend */
+				if (!zone_watermark_ok(zone, order,
+						zone->pages_high, end_zone, 0, 0))
+					all_zones_ok = 0;
+			}
+			zone->temp_priority = priority;
+			if (zone->prev_priority > priority)
+				zone->prev_priority = priority;
+			sc.nr_scanned = 0;
+			sc.nr_reclaimed = 0;
+			sc.priority = priority;
+			sc.swap_cluster_max = nr_pages? nr_pages : SWAP_CLUSTER_MAX;
+			shrink_zone(zone, &sc);
+			reclaim_state->reclaimed_slab = 0;
+			shrink_slab(sc.nr_scanned, GFP_KERNEL, lru_pages);
+			sc.nr_reclaimed += reclaim_state->reclaimed_slab;
+			total_reclaimed += sc.nr_reclaimed;
+			total_scanned += sc.nr_scanned;
+			if (zone->all_unreclaimable)
+				continue;
+			if (zone->pages_scanned >= (zone->nr_active +
+							zone->nr_inactive) * 4)
+				zone->all_unreclaimable = 1;
+			/*
+			 * If we've done a decent amount of scanning and
+			 * the reclaim ratio is low, start doing writepage
+			 * even in laptop mode
+			 */
+			if (total_scanned > SWAP_CLUSTER_MAX * 2 &&
+			    total_scanned > total_reclaimed+total_reclaimed/2)
+				sc.may_writepage = 1;
+		}
+		if (nr_pages && to_free > total_reclaimed)
+			continue;	/* swsusp: need to do more work */
+		if (all_zones_ok)
+			break;		/* kswapd: all done */
+		/*
+		 * OK, kswapd is getting into trouble.  Take a nap, then take
+		 * another pass across the zones.
+		 */
+		if (total_scanned && priority < DEF_PRIORITY - 2)
+			blk_congestion_wait(WRITE, HZ/10);
+
+		/*
+		 * We do this so kswapd doesn't build up large priorities for
+		 * example when it is freeing in parallel with allocators. It
+		 * matches the direct reclaim path behaviour in terms of impact
+		 * on zone->*_priority.
+		 */
+		if ((total_reclaimed >= SWAP_CLUSTER_MAX) && (!nr_pages))
+			break;
+	}
+out:
+	for (i = 0; i < pgdat->nr_zones; i++) {
+		struct zone *zone = pgdat->node_zones + i;
+
+		zone->prev_priority = zone->temp_priority;
+	}
+	if (!all_zones_ok) {
+		cond_resched();
+		goto loop_again;
+	}
+
+	return total_reclaimed;
+}
+
+/*
+ * The background pageout daemon, started as a kernel thread
+ * from the init process. 
+ *
+ * This basically trickles 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.
+ */
+static int kswapd(void *p)
+{
+	unsigned long order;
+	pg_data_t *pgdat = (pg_data_t*)p;
+	struct task_struct *tsk = current;
+	DEFINE_WAIT(wait);
+	struct reclaim_state reclaim_state = {
+		.reclaimed_slab = 0,
+	};
+	cpumask_t cpumask;
+
+	daemonize("kswapd%d", pgdat->node_id);
+	cpumask = node_to_cpumask(pgdat->node_id);
+	if (!cpus_empty(cpumask))
+		set_cpus_allowed(tsk, cpumask);
+	current->reclaim_state = &reclaim_state;
+
+	/*
+	 * 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 "__alloc_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|PF_KSWAPD;
+
+	order = 0;
+	for ( ; ; ) {
+		unsigned long new_order;
+		if (current->flags & PF_FREEZE)
+			refrigerator(PF_FREEZE);
+
+		prepare_to_wait(&pgdat->kswapd_wait, &wait, TASK_INTERRUPTIBLE);
+		new_order = pgdat->kswapd_max_order;
+		pgdat->kswapd_max_order = 0;
+		if (order < new_order) {
+			/*
+			 * Don't sleep if someone wants a larger 'order'
+			 * allocation
+			 */
+			order = new_order;
+		} else {
+			schedule();
+			order = pgdat->kswapd_max_order;
+		}
+		finish_wait(&pgdat->kswapd_wait, &wait);
+
+		balance_pgdat(pgdat, 0, order);
+	}
+	return 0;
+}
+
+/*
+ * A zone is low on free memory, so wake its kswapd task to service it.
+ */
+void wakeup_kswapd(struct zone *zone, int order)
+{
+	pg_data_t *pgdat;
+
+	if (zone->present_pages == 0)
+		return;
+
+	pgdat = zone->zone_pgdat;
+	if (zone_watermark_ok(zone, order, zone->pages_low, 0, 0, 0))
+		return;
+	if (pgdat->kswapd_max_order < order)
+		pgdat->kswapd_max_order = order;
+	if (!cpuset_zone_allowed(zone))
+		return;
+	if (!waitqueue_active(&zone->zone_pgdat->kswapd_wait))
+		return;
+	wake_up_interruptible(&zone->zone_pgdat->kswapd_wait);
+}
+
+#ifdef CONFIG_PM
+/*
+ * Try to free `nr_pages' of memory, system-wide.  Returns the number of freed
+ * pages.
+ */
+int shrink_all_memory(int nr_pages)
+{
+	pg_data_t *pgdat;
+	int nr_to_free = nr_pages;
+	int ret = 0;
+	struct reclaim_state reclaim_state = {
+		.reclaimed_slab = 0,
+	};
+
+	current->reclaim_state = &reclaim_state;
+	for_each_pgdat(pgdat) {
+		int freed;
+		freed = balance_pgdat(pgdat, nr_to_free, 0);
+		ret += freed;
+		nr_to_free -= freed;
+		if (nr_to_free <= 0)
+			break;
+	}
+	current->reclaim_state = NULL;
+	return ret;
+}
+#endif
+
+#ifdef CONFIG_HOTPLUG_CPU
+/* It's optimal to keep kswapds on the same CPUs as their memory, but
+   not required for correctness.  So if the last cpu in a node goes
+   away, we get changed to run anywhere: as the first one comes back,
+   restore their cpu bindings. */
+static int __devinit cpu_callback(struct notifier_block *nfb,
+				  unsigned long action,
+				  void *hcpu)
+{
+	pg_data_t *pgdat;
+	cpumask_t mask;
+
+	if (action == CPU_ONLINE) {
+		for_each_pgdat(pgdat) {
+			mask = node_to_cpumask(pgdat->node_id);
+			if (any_online_cpu(mask) != NR_CPUS)
+				/* One of our CPUs online: restore mask */
+				set_cpus_allowed(pgdat->kswapd, mask);
+		}
+	}
+	return NOTIFY_OK;
+}
+#endif /* CONFIG_HOTPLUG_CPU */
+
+static int __init kswapd_init(void)
+{
+	pg_data_t *pgdat;
+	swap_setup();
+	for_each_pgdat(pgdat)
+		pgdat->kswapd
+		= find_task_by_pid(kernel_thread(kswapd, pgdat, CLONE_KERNEL));
+	total_memory = nr_free_pagecache_pages();
+	hotcpu_notifier(cpu_callback, 0);
+	return 0;
+}
+
+module_init(kswapd_init)