X-Git-Url: https://git.lttng.org/?a=blobdiff_plain;f=rculfhash-mm-mmap.c;h=a8fadf0696de5e743fe56c4190cc0e4d8e1578b1;hb=refs%2Fheads%2Fstable-0.8;hp=542c884e9f576c4dae45186b4fa0b4849cbd4eb8;hpb=b0b5525153fce8abae07b9573da1d5169e02eb2b;p=userspace-rcu.git

diff --git a/rculfhash-mm-mmap.c b/rculfhash-mm-mmap.c
index 542c884..a8fadf0 100644
--- a/rculfhash-mm-mmap.c
+++ b/rculfhash-mm-mmap.c
@@ -24,8 +24,34 @@
 #include <sys/mman.h>
 #include "rculfhash-internal.h"
 
-/* reserve inaccessible memory space without allocation any memory */
-static void *memory_map(size_t length)
+#ifndef MAP_ANONYMOUS
+#define MAP_ANONYMOUS		MAP_ANON
+#endif
+
+/*
+ * The allocation scheme used by the mmap based RCU hash table is to make a
+ * large unaccessible mapping to reserve memory without allocating it.
+ * Then smaller chunks are allocated by overlapping read/write mappings which
+ * do allocate memory. Deallocation is done by an overlapping unaccessible
+ * mapping.
+ *
+ * This scheme was tested on Linux, macOS and Solaris. However, on Cygwin the
+ * mmap wrapper is based on the Windows NtMapViewOfSection API which doesn't
+ * support overlapping mappings.
+ *
+ * An alternative to the overlapping mappings is to use mprotect to change the
+ * protection on chunks of the large mapping, read/write to allocate and none
+ * to deallocate. This works perfecty on Cygwin and Solaris but on Linux a
+ * call to madvise is also required to deallocate and it just doesn't work on
+ * macOS.
+ *
+ * For this reason, we keep to original scheme on all platforms except Cygwin.
+ */
+
+
+/* Reserve inaccessible memory space without allocating it */
+static
+void *memory_map(size_t length)
 {
 	void *ret = mmap(NULL, length, PROT_NONE,
 			MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
@@ -34,16 +60,47 @@ static void *memory_map(size_t length)
 	return ret;
 }
 
-static void memory_unmap(void *ptr, size_t length)
+static
+void memory_unmap(void *ptr, size_t length)
 {
-	int ret = munmap(ptr, length);
+	int ret __attribute__((unused));
+
+	ret = munmap(ptr, length);
 
 	assert(ret == 0);
 }
 
-static void memory_populate(void *ptr, size_t length)
+#ifdef __CYGWIN__
+/* Set protection to read/write to allocate a memory chunk */
+static
+void memory_populate(void *ptr, size_t length)
+{
+	int ret __attribute__((unused));
+
+	ret = mprotect(ptr, length, PROT_READ | PROT_WRITE);
+
+	assert(!ret);
+}
+
+/* Set protection to none to deallocate a memory chunk */
+static
+void memory_discard(void *ptr, size_t length)
+{
+	int ret __attribute__((unused));
+
+	ret = mprotect(ptr, length, PROT_NONE);
+
+	assert(!ret);
+}
+
+#else /* __CYGWIN__ */
+
+static
+void memory_populate(void *ptr, size_t length)
 {
-	void *ret = mmap(ptr, length, PROT_READ | PROT_WRITE,
+	void *ret __attribute__((unused));
+
+	ret = mmap(ptr, length, PROT_READ | PROT_WRITE,
 			MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 
 	assert(ret == ptr);
@@ -53,13 +110,17 @@ static void memory_populate(void *ptr, size_t length)
  * Discard garbage memory and avoid system save it when try to swap it out.
  * Make it still reserved, inaccessible.
  */
-static void memory_discard(void *ptr, size_t length)
+static
+void memory_discard(void *ptr, size_t length)
 {
-	void *ret = mmap(ptr, length, PROT_NONE,
+	void *ret __attribute__((unused));
+
+	ret = mmap(ptr, length, PROT_NONE,
 			MAP_FIXED | MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 
 	assert(ret == ptr);
 }
+#endif /* __CYGWIN__ */
 
 static
 void cds_lfht_alloc_bucket_table(struct cds_lfht *ht, unsigned long order)
@@ -125,9 +186,9 @@ static
 struct cds_lfht *alloc_cds_lfht(unsigned long min_nr_alloc_buckets,
 		unsigned long max_nr_buckets)
 {
-	struct cds_lfht *ht;
-	unsigned long page_bucket_size = getpagesize() / sizeof(*ht->tbl_mmap);
+	unsigned long page_bucket_size;
 
+	page_bucket_size = getpagesize() / sizeof(struct cds_lfht_node);
 	if (max_nr_buckets <= page_bucket_size) {
 		/* small table */
 		min_nr_alloc_buckets = max_nr_buckets;
@@ -137,19 +198,9 @@ struct cds_lfht *alloc_cds_lfht(unsigned long min_nr_alloc_buckets,
 					page_bucket_size);
 	}
 
-	ht = calloc(1, sizeof(struct cds_lfht));
-	assert(ht);
-
-	ht->mm = &cds_lfht_mm_mmap;
-
-	ht->min_nr_alloc_buckets = min_nr_alloc_buckets;
-	ht->min_alloc_buckets_order =
-			get_count_order_ulong(min_nr_alloc_buckets);
-	ht->max_nr_buckets = max_nr_buckets;
-
-	ht->bucket_at = bucket_at;
-
-	return ht;
+	return __default_alloc_cds_lfht(
+			&cds_lfht_mm_mmap, sizeof(struct cds_lfht),
+			min_nr_alloc_buckets, max_nr_buckets);
 }
 
 const struct cds_lfht_mm_type cds_lfht_mm_mmap = {