x86: introduce page pool in cpa

DEBUG_PAGEALLOC was not possible on 64-bit due to its early-bootup
hardcoded reliance on PSE pages, and the unrobustness of the runtime
splitup of large pages. The splitup ended in recursive calls to
alloc_pages() when a page for a pte split was requested.

Avoid the recursion with a preallocated page pool, which is used to
split up large mappings and gets refilled in the return path of
kernel_map_pages after the split has been done. The size of the page
pool is adjusted to the available memory.

This part just implements the page pool and the initialization w/o
using it yet.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 81 insertions, 1 deletions

diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
index eb2a54415a77..831462c3bc35 100644
--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -8,6 +8,7 @@
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/mm.h>
+#include <linux/interrupt.h>
 
 #include <asm/e820.h>
 #include <asm/processor.h>
@@ -336,6 +337,77 @@ out_unlock:
         return do_split;
 }
 
+static LIST_HEAD(page_pool);
+static unsigned long pool_size, pool_pages, pool_low;
+static unsigned long pool_used, pool_failed, pool_refill;
+
+static void cpa_fill_pool(void)
+{
+        struct page *p;
+        gfp_t gfp = GFP_KERNEL;
+
+        /* 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:
+         */
+        if (pool_pages >= pool_size || test_and_set_bit_lock(0, &pool_refill))
+                return;
+
+#ifdef CONFIG_DEBUG_PAGEALLOC
+        /*
+         * We could do:
+         * gfp = in_atomic() ? GFP_ATOMIC : GFP_KERNEL;
+         * but this fails on !PREEMPT kernels
+         */
+        gfp =  GFP_ATOMIC | __GFP_NORETRY | __GFP_NOWARN;
+#endif
+
+        while (pool_pages < pool_size) {
+                p = alloc_pages(gfp, 0);
+                if (!p) {
+                        pool_failed++;
+                        break;
+                }
+                spin_lock_irq(&pgd_lock);
+                list_add(&p->lru, &page_pool);
+                pool_pages++;
+                spin_unlock_irq(&pgd_lock);
+        }
+        clear_bit_unlock(0, &pool_refill);
+}
+
+#define SHIFT_MB                (20 - PAGE_SHIFT)
+#define ROUND_MB_GB             ((1 << 10) - 1)
+#define SHIFT_MB_GB             10
+#define POOL_PAGES_PER_GB       16
+
+void __init cpa_init(void)
+{
+        struct sysinfo si;
+        unsigned long gb;
+
+        si_meminfo(&si);
+        /*
+         * Calculate the number of pool pages:
+         *
+         * Convert totalram (nr of pages) to MiB and round to the next
+         * 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;
+        pool_low = pool_size;
+
+        cpa_fill_pool();
+        printk(KERN_DEBUG
+               "CPA: page pool initialized %lu of %lu pages preallocated\n",
+               pool_pages, pool_size);
+}
+
 static int split_large_page(pte_t *kpte, unsigned long address)
 {
         unsigned long flags, pfn, pfninc = 1;
@@ -600,7 +672,7 @@ static int change_page_attr_set_clr(unsigned long addr, int numpages,
          * Check whether we really changed something:
          */
         if (!cpa.flushtlb)
-                return ret;
+                goto out;
 
         /*
          * No need to flush, when we did not set any of the caching
@@ -619,6 +691,8 @@ static int change_page_attr_set_clr(unsigned long addr, int numpages,
         else
                 cpa_flush_all(cache);
 
+out:
+        cpa_fill_pool();
         return ret;
 }
 
@@ -772,6 +846,12 @@ void kernel_map_pages(struct page *page, int numpages, int enable)
          * but that can deadlock->flush only current cpu:
          */
         __flush_tlb_all();
+
+        /*
+         * Try to refill the page pool here. We can do this only after
+         * the tlb flush.
+         */
+        cpa_fill_pool();
 }
 #endif