x86: make DEBUG_PAGEALLOC and CPA more robust

Use PF_MEMALLOC to prevent recursive calls in the DBEUG_PAGEALLOC
case. This makes the code simpler and more robust against allocation
failures.

This fixes the following fallback to non-mmconfig:

   http://lkml.org/lkml/2008/2/20/551
   http://bugzilla.kernel.org/show_bug.cgi?id=10083

Also, for DEBUG_PAGEALLOC=n reduce the pool size to one page.
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/mm/pageattr.c

@@ -44,6 +44,12 @@ static inline unsigned long highmap_end_pfn(void)
 
 #endif
 
+#ifdef CONFIG_DEBUG_PAGEALLOC
+# define debug_pagealloc 1
+#else
+# define debug_pagealloc 0
+#endif
+
 static inline int
 within(unsigned long addr, unsigned long start, unsigned long end)
 {
@@ -355,45 +361,48 @@ try_preserve_large_page(pte_t *kpte, unsigned long address,
 
 static LIST_HEAD(page_pool);
 static unsigned long pool_size, pool_pages, pool_low;
-static unsigned long pool_used, pool_failed, pool_refill;
+static unsigned long pool_used, pool_failed;
 
-static void cpa_fill_pool(void)
+static void cpa_fill_pool(struct page **ret)
 {
-	struct page *p;
 	gfp_t gfp = GFP_KERNEL;
+	unsigned long flags;
+	struct page *p;
 
-	/* Do not allocate from interrupt context */
-	if (in_irq() || irqs_disabled())
-		return;
 	/*
-	 * Check unlocked. I does not matter when we have one more
-	 * page in the pool. The bit lock avoids recursive pool
-	 * allocations:
+	 * Avoid recursion (on debug-pagealloc) and also signal
+	 * our priority to get to these pagetables:
 	 */
-	if (pool_pages >= pool_size || test_and_set_bit_lock(0, &pool_refill))
+	if (current->flags & PF_MEMALLOC)
 		return;
+	current->flags |= PF_MEMALLOC;
 
-#ifdef CONFIG_DEBUG_PAGEALLOC
 	/*
-	 * We could do:
-	 * gfp = in_atomic() ? GFP_ATOMIC : GFP_KERNEL;
-	 * but this fails on !PREEMPT kernels
+	 * Allocate atomically from atomic contexts:
 	 */
-	gfp =  GFP_ATOMIC | __GFP_NORETRY | __GFP_NOWARN;
-#endif
+	if (in_atomic() || irqs_disabled() || debug_pagealloc)
+		gfp =  GFP_ATOMIC | __GFP_NORETRY | __GFP_NOWARN;
 
-	while (pool_pages < pool_size) {
+	while (pool_pages < pool_size || (ret && !*ret)) {
 		p = alloc_pages(gfp, 0);
 		if (!p) {
 			pool_failed++;
 			break;
 		}
-		spin_lock_irq(&pgd_lock);
+		/*
+		 * If the call site needs a page right now, provide it:
+		 */
+		if (ret && !*ret) {
+			*ret = p;
+			continue;
+		}
+		spin_lock_irqsave(&pgd_lock, flags);
 		list_add(&p->lru, &page_pool);
 		pool_pages++;
-		spin_unlock_irq(&pgd_lock);
+		spin_unlock_irqrestore(&pgd_lock, flags);
 	}
-	clear_bit_unlock(0, &pool_refill);
+
+	current->flags &= ~PF_MEMALLOC;
 }
 
 #define SHIFT_MB		(20 - PAGE_SHIFT)
@@ -414,11 +423,15 @@ void __init cpa_init(void)
 	 * GiB. Shift MiB to Gib and multiply the result by
 	 * POOL_PAGES_PER_GB:
 	 */
-	gb = ((si.totalram >> SHIFT_MB) + ROUND_MB_GB) >> SHIFT_MB_GB;
-	pool_size = POOL_PAGES_PER_GB * gb;
+	if (debug_pagealloc) {
+		gb = ((si.totalram >> SHIFT_MB) + ROUND_MB_GB) >> SHIFT_MB_GB;
+		pool_size = POOL_PAGES_PER_GB * gb;
+	} else {
+		pool_size = 1;
+	}
 	pool_low = pool_size;
 
-	cpa_fill_pool();
+	cpa_fill_pool(NULL);
 	printk(KERN_DEBUG
 	       "CPA: page pool initialized %lu of %lu pages preallocated\n",
 	       pool_pages, pool_size);
@@ -440,16 +453,20 @@ static int split_large_page(pte_t *kpte, unsigned long address)
 	spin_lock_irqsave(&pgd_lock, flags);
 	if (list_empty(&page_pool)) {
 		spin_unlock_irqrestore(&pgd_lock, flags);
-		return -ENOMEM;
+		base = NULL;
+		cpa_fill_pool(&base);
+		if (!base)
+			return -ENOMEM;
+		spin_lock_irqsave(&pgd_lock, flags);
+	} else {
+		base = list_first_entry(&page_pool, struct page, lru);
+		list_del(&base->lru);
+		pool_pages--;
+
+		if (pool_pages < pool_low)
+			pool_low = pool_pages;
 	}
 
-	base = list_first_entry(&page_pool, struct page, lru);
-	list_del(&base->lru);
-	pool_pages--;
-
-	if (pool_pages < pool_low)
-		pool_low = pool_pages;
-
 	/*
 	 * Check for races, another CPU might have split this page
 	 * up for us already:
@@ -734,7 +751,8 @@ static int change_page_attr_set_clr(unsigned long addr, int numpages,
 		cpa_flush_all(cache);
 
 out:
-	cpa_fill_pool();
+	cpa_fill_pool(NULL);
+
 	return ret;
 }
 
@@ -897,7 +915,7 @@ void kernel_map_pages(struct page *page, int numpages, int enable)
 	 * Try to refill the page pool here. We can do this only after
 	 * the tlb flush.
 	 */
-	cpa_fill_pool();
+	cpa_fill_pool(NULL);
 }
 
 #ifdef CONFIG_HIBERNATION