[PATCH] earlier allocation of order 0 pages from pcp in __alloc_pages

[Seth, Rohit]

	[PATCH]: Try to service a order 0 page request in __alloc_pages from the pcp list before checking the aone_watermarks.

        Try to service a order 0 page request from pcp list.  This will allow us to not check and possibly start the reclaim activity when there are free pages present on the pcp.  This early allocation does not try to replenish an empty pcp.

        Signed-off-by: Rohit Seth <rohit.seth@xxxxxxxxx>

--- linux-2.6.14-rc2-mm1.org/mm/page_alloc.c	2005-09-27 10:03:51.000000000 -0700
+++ linux-2.6.14-rc2-mm1/mm/page_alloc.c	2005-09-28 17:38:15.000000000 -0700
@@ -716,6 +716,39 @@
 		clear_highpage(page + i);
 }
 
+/* This routine allocates a order 0 page from cpu's pcp list when one is present.
+ * It does not try to remove the pages from zone_free_list as the zone low
+ * water mark has not yet been checked.
+ */
+
+static struct page *
+remove_from_pcp(struct zone *zone, unsigned int __nocast gfp_flags)
+{
+	unsigned long flags;
+	struct per_cpu_pages *pcp;
+	struct page *page = NULL;
+	int cold = !!(gfp_flags & __GFP_COLD);
+
+	pcp = &zone_pcp(zone, get_cpu())->pcp[cold];
+	local_irq_save(flags);
+	if (pcp->count > pcp->low) {
+		page = list_entry(pcp->list.next, struct page, lru);
+		list_del(&page->lru);
+		pcp->count--;
+	}
+	local_irq_restore(flags);
+	put_cpu();
+
+	if (page != NULL) {
+		mod_page_state_zone(zone, pgalloc, 1 );
+		prep_new_page(page, 0);
+
+		if (gfp_flags & __GFP_ZERO)
+			prep_zero_page(page, 0, gfp_flags);
+	}
+	return page;
+}
+
 /*
  * Really, prep_compound_page() should be called from __rmqueue_bulk().  But
  * we cheat by calling it from here, in the order > 0 path.  Saves a branch
@@ -905,6 +938,12 @@
 		if (!cpuset_zone_allowed(z, __GFP_HARDWALL))
 			continue;
 
+		if (order == 0) {
+			page = remove_from_pcp(z, gfp_mask);
+			if (page)
+				goto got_pg;
+		}
+
 		/*
 		 * If the zone is to attempt early page reclaim then this loop
 		 * will try to reclaim pages and check the watermark a second
-
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