[PATCH] alloc_pages cleanup

Cleanup patch from Martin Bligh: convert some loops which want to be
`for' loops into that, and add some commentary.

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 2acac7c0aa804676247ce53fffeb878108daeb34..8991e2ae603758c7ff29099b193e25ac397db03d 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -323,22 +323,23 @@ balance_classzone(zone_t * classzone, unsigned int gfp_mask,
 struct page * __alloc_pages(unsigned int gfp_mask, unsigned int order, zonelist_t *zonelist)
 {
        unsigned long min;
-       zone_t **zone, * classzone;
+       zone_t **zones, *classzone;
        struct page * page;
-       int freed;
+       int freed, i;
 
        KERNEL_STAT_ADD(pgalloc, 1<<order);
 
-       zone = zonelist->zones;
-       classzone = *zone;
-       if (classzone == NULL)
+       zones = zonelist->zones;  /* the list of zones suitable for gfp_mask */
+       classzone = zones[0]; 
+       if (classzone == NULL)    /* no zones in the zonelist */
                return NULL;
+
+       /* Go through the zonelist once, looking for a zone with enough free */
        min = 1UL << order;
-       for (;;) {
-               zone_t *z = *(zone++);
-               if (!z)
-                       break;
+       for (i = 0; zones[i] != NULL; i++) {
+               zone_t *z = zones[i];
 
+               /* the incremental min is allegedly to discourage fallback */
                min += z->pages_low;
                if (z->free_pages > min) {
                        page = rmqueue(z, order);
@@ -349,16 +350,15 @@ struct page * __alloc_pages(unsigned int gfp_mask, unsigned int order, zonelist_
 
        classzone->need_balance = 1;
        mb();
+       /* we're somewhat low on memory, failed to find what we needed */
        if (waitqueue_active(&kswapd_wait))
                wake_up_interruptible(&kswapd_wait);
 
-       zone = zonelist->zones;
+       /* Go through the zonelist again, taking __GFP_HIGH into account */
        min = 1UL << order;
-       for (;;) {
+       for (i = 0; zones[i] != NULL; i++) {
                unsigned long local_min;
-               zone_t *z = *(zone++);
-               if (!z)
-                       break;
+               zone_t *z = zones[i];
 
                local_min = z->pages_min;
                if (gfp_mask & __GFP_HIGH)
@@ -375,11 +375,9 @@ struct page * __alloc_pages(unsigned int gfp_mask, unsigned int order, zonelist_
 
 rebalance:
        if (current->flags & (PF_MEMALLOC | PF_MEMDIE)) {
-               zone = zonelist->zones;
-               for (;;) {
-                       zone_t *z = *(zone++);
-                       if (!z)
-                               break;
+               /* go through the zonelist yet again, ignoring mins */
+               for (i = 0; zones[i] != NULL; i++) {
+                       zone_t *z = zones[i];
 
                        page = rmqueue(z, order);
                        if (page)
@@ -403,12 +401,10 @@ nopage:
        if (page)
                return page;
 
-       zone = zonelist->zones;
+       /* go through the zonelist yet one more time */
        min = 1UL << order;
-       for (;;) {
-               zone_t *z = *(zone++);
-               if (!z)
-                       break;
+       for (i = 0; zones[i] != NULL; i++) {
+               zone_t *z = zones[i];
 
                min += z->pages_min;
                if (z->free_pages > min) {