[rfc][patch 4/4] s390: mixedmap_refcount_pfn implementation using list walk

[Carsten Otte <cotte@de.ibm.com>]

This patch implements mixedmap_refcount_pfn() for s390 architecture using
list-walk. This is merely meant to be a proof of concept, because we do
prefer spending one valuable pte bit to speed this up.

Signed-off-by: Carsten Otte <cotte@de.ibm.com>
--- 
Index: linux-2.6/arch/s390/mm/vmem.c
===================================================================
--- linux-2.6.orig/arch/s390/mm/vmem.c
+++ linux-2.6/arch/s390/mm/vmem.c
@@ -339,6 +339,26 @@ out:
 	return ret;
 }
 
+int mixedmap_refcount_pfn(unsigned long pfn)
+{
+	int rc;
+	struct memory_segment *tmp;
+
+	mutex_lock(&vmem_mutex);
+
+	list_for_each_entry(tmp, &mem_segs, list) {
+		if ((tmp->start >= pfn << PAGE_SHIFT) &&
+		    (tmp->start + tmp->size - 1 < pfn << PAGE_SHIFT)) {
+			rc = 0;
+			goto out;
+		}
+	}
+	rc = 1;
+out:
+	mutex_unlock(&vmem_mutex);
+	return rc;
+}
+
 /*
  * map whole physical memory to virtual memory (identity mapping)
  */
Index: linux-2.6/include/linux/mm.h
===================================================================
--- linux-2.6.orig/include/linux/mm.h
+++ linux-2.6/include/linux/mm.h
@@ -28,6 +28,13 @@ extern unsigned long num_physpages;
 extern void * high_memory;
 extern int page_cluster;
 
+/*
+ * This callback is only needed when using VM_MIXEDMAP. It is used by common
+ * code to check if a pfn needs refcounting in the corresponding struct page.
+ */
+extern int mixedmap_refcount_pfn(unsigned long pfn);
+
+
 #ifdef CONFIG_SYSCTL
 extern int sysctl_legacy_va_layout;
 #else


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