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 <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/mm/init_32.c

···
 	if (boot_cpu_data.wp_works_ok < 0)
 		test_wp_bit();
 
+	cpa_init();
+
 	/*
 	 * Subtle. SMP is doing it's boot stuff late (because it has to
 	 * fork idle threads) - but it also needs low mappings for the

arch/x86/mm/init_64.c

···
 		reservedpages << (PAGE_SHIFT-10),
 		datasize >> 10,
 		initsize >> 10);
+
+	cpa_init();
 }
 
 void free_init_pages(char *what, unsigned long begin, unsigned long end)

arch/x86/mm/pageattr.c

···
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/mm.h>
+#include <linux/interrupt.h>
 
 #include <asm/e820.h>
 #include <asm/processor.h>
···
 	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;
···
 	 * 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
···
 	else
 		cpa_flush_all(cache);
 
+out:
+	cpa_fill_pool();
 	return ret;
 }
 
···
 	 * 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
 

include/asm-x86/cacheflush.h

···
 
 void clflush_cache_range(void *addr, unsigned int size);
 
+void cpa_init(void);
+
 #ifdef CONFIG_DEBUG_RODATA
 void mark_rodata_ro(void);
 #endif