Make the LRU arithmetic more explicit.  Hopefully this will make
the code a little easier to read and less prone to future errors.

Signed-off-by: Rik van Riel <[EMAIL PROTECTED]>

Index: linux-2.6.23-mm1/include/linux/mm_inline.h
===================================================================
--- linux-2.6.23-mm1.orig/include/linux/mm_inline.h
+++ linux-2.6.23-mm1/include/linux/mm_inline.h
@@ -28,7 +28,7 @@ static inline int page_file_cache(struct
                return 0;
 
        /* The page is page cache backed by a normal filesystem. */
-       return (LRU_INACTIVE_FILE - LRU_INACTIVE_ANON);
+       return LRU_FILE;
 }
 
 static inline void
Index: linux-2.6.23-mm1/mm/swap.c
===================================================================
--- linux-2.6.23-mm1.orig/mm/swap.c
+++ linux-2.6.23-mm1/mm/swap.c
@@ -180,12 +180,12 @@ void fastcall activate_page(struct page 
 
        spin_lock_irq(&zone->lru_lock);
        if (PageLRU(page) && !PageActive(page)) {
-               int l = LRU_INACTIVE_ANON;
+               int l = LRU_BASE;
                l += page_file_cache(page);
                del_page_from_lru_list(zone, page, l);
 
                SetPageActive(page);
-               l += LRU_ACTIVE_ANON - LRU_INACTIVE_ANON;
+               l += LRU_ACTIVE;
                add_page_to_lru_list(zone, page, l);
                __count_vm_event(PGACTIVATE);
                mem_cgroup_move_lists(page_get_page_cgroup(page), true);
Index: linux-2.6.23-mm1/mm/vmscan.c
===================================================================
--- linux-2.6.23-mm1.orig/mm/vmscan.c
+++ linux-2.6.23-mm1/mm/vmscan.c
@@ -786,11 +786,11 @@ static unsigned long isolate_pages_globa
                                        struct mem_cgroup *mem_cont,
                                        int active, int file)
 {
-       int l = LRU_INACTIVE_ANON;
+       int l = LRU_BASE;
        if (active)
-               l += LRU_ACTIVE_ANON - LRU_INACTIVE_ANON;
+               l += LRU_ACTIVE;
        if (file)
-               l += LRU_INACTIVE_FILE - LRU_INACTIVE_ANON;
+               l += LRU_FILE;
        return isolate_lru_pages(nr, &z->list[l], dst, scanned, order,
                                                                mode, !!file);
 }
@@ -842,7 +842,7 @@ int isolate_lru_page(struct page *page)
 
                spin_lock_irq(&zone->lru_lock);
                if (PageLRU(page) && get_page_unless_zero(page)) {
-                       int l = LRU_INACTIVE_ANON;
+                       int l = LRU_BASE;
                        ret = 0;
                        ClearPageLRU(page);
 
@@ -938,19 +938,19 @@ static unsigned long shrink_inactive_lis
                 * Put back any unfreeable pages.
                 */
                while (!list_empty(&page_list)) {
-                       int l = LRU_INACTIVE_ANON;
+                       int l = LRU_BASE;
                        page = lru_to_page(&page_list);
                        VM_BUG_ON(PageLRU(page));
                        SetPageLRU(page);
                        list_del(&page->lru);
                        if (file) {
-                               l += LRU_INACTIVE_FILE - LRU_INACTIVE_ANON;
+                               l += LRU_FILE;
                                zone->recent_rotated_file += sc->activated;
                        } else {
                                zone->recent_rotated_anon += sc->activated;
                        }
                        if (PageActive(page))
-                               l += LRU_ACTIVE_ANON - LRU_INACTIVE_ANON;
+                               l += LRU_ACTIVE;
                        add_page_to_lru_list(zone, page, l);
                        if (!pagevec_add(&pvec, page)) {
                                spin_unlock_irq(&zone->lru_lock);
@@ -1051,7 +1051,7 @@ static void shrink_active_list(unsigned 
         */
        pagevec_init(&pvec, 1);
        pgmoved = 0;
-       l = LRU_INACTIVE_ANON + file * (LRU_INACTIVE_FILE - LRU_INACTIVE_ANON);
+       l = LRU_BASE + file * LRU_FILE;
        spin_lock_irq(&zone->lru_lock);
        while (!list_empty(&list[LRU_INACTIVE_ANON])) {
                page = lru_to_page(&list[LRU_INACTIVE_ANON]);
@@ -1083,7 +1083,7 @@ static void shrink_active_list(unsigned 
        if (buffer_heads_over_limit)
                pagevec_strip(&pvec);
        pgmoved = 0;
-       l = LRU_ACTIVE_ANON + file * (LRU_ACTIVE_FILE - LRU_ACTIVE_ANON);
+       l = LRU_ACTIVE + file * LRU_FILE;
        spin_lock_irq(&zone->lru_lock);
        while (!list_empty(&list[LRU_ACTIVE_ANON])) {
                page = lru_to_page(&list[LRU_ACTIVE_ANON]);
Index: linux-2.6.23-mm1/include/linux/mmzone.h
===================================================================
--- linux-2.6.23-mm1.orig/include/linux/mmzone.h
+++ linux-2.6.23-mm1/include/linux/mmzone.h
@@ -107,11 +107,22 @@ enum zone_stat_item {
 #endif
        NR_VM_ZONE_STAT_ITEMS };
 
+/*
+ * We do arithmetic on the LRU lists in various places in the code,
+ * so it is important to keep the active lists LRU_ACTIVE higher in
+ * the array than the corresponding inactive lists, and to keep
+ * the *_FILE lists LRU_FILE higher than the corresponding _ANON lists.
+ */
+#define LRU_BASE 0
+#define LRU_ANON LRU_BASE
+#define LRU_ACTIVE 1
+#define LRU_FILE 2
+
 enum lru_list {
-       LRU_INACTIVE_ANON,      /* must be first enum  */
-       LRU_ACTIVE_ANON,        /* must match order of NR_[IN]ACTIVE_* */
-       LRU_INACTIVE_FILE,      /*  "     "     "   "       "          */
-       LRU_ACTIVE_FILE,        /*  "     "     "   "       "          */
+       LRU_INACTIVE_ANON = LRU_BASE,
+       LRU_ACTIVE_ANON = LRU_BASE + LRU_ACTIVE,
+       LRU_INACTIVE_FILE = LRU_BASE + LRU_FILE,
+       LRU_ACTIVE_FILE = LRU_BASE + LRU_FILE + LRU_ACTIVE,
        NR_LRU_LISTS };
 
 #define for_each_lru(l) for (l = 0; l < NR_LRU_LISTS; l++)
-
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