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>

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index 464d8fc21ce69b67d8d8bf057f5a57ef6a84c677..14e48b5a94ba193c1cb4acc667482e05905d373e 100644 (file)
--- a/arch/x86/mm/pageattr.c
+++ b/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 @@ out_unlock:
 
 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