threaded mode: madvise() map1 to `MADV_DONTNEED | MADV_COLD` after threads completed.

Fortune for fcmp's current commit: Half blessing − 半吉

include/fcmp.h

@@ -11,7 +11,7 @@
 
 #ifdef DEBUG
 #define __name(d) #d
-#define dprintf(fmt, ...) printf("[dbg @" __FILE__ "->%s:%d] " fmt "\n", __func__, __LINE__ __VA_OPT__(,) __VA_ARGS__)
+#define dprintf(fmt, ...) printf("[dbg @" __FILE__ "->%s:%d] " fmt "\n", __func__, __LINE__, ## __VA_ARGS__)
 #else
 #define dprintf(fmt, ...)
 #endif

include/map.h

@@ -18,6 +18,9 @@ typedef struct mmap {
 int open_and_map(const char* file, mmap_t* restrict ptr);
 int unmap_and_close(mmap_t map);
 int set_preload_map(mmap_t* restrict map);
+/// Undo a previous call to `set_preload_map()`.
+/// *freeing* (1 - yes, 0, no) - If the next operation on the map will be `unmap_and_close()`, advise the kernel to drop the mapped pages whenever it wants. Do not specify this if you will use the map again after this call.
+int unset_preload_map(mmap_t* restrict map, int freeing);
 
 #ifdef _cplusplus
 }

src/main.c

@@ -27,6 +27,17 @@ _FORCE_INLINE const void* die_with_usage_if_null(const void* ptr)
 	else return ptr;
 }
 
+static void unprep_map(mmap_t* restrict map, bool free)
+{
+	//TODO: Should we actually bother to call this before unmapping?
+	
+	if(!unset_preload_map(map, (int)free))
+		fprintf(stderr, "Error: failed to unprep map %p (%d)%s, continuing anyway\n",
+			map->ptr, map->fd,
+			(free ? " before closing" : ""));
+	else dprintf("unprep'd %p (%d)", map->ptr, map->fd);
+}
+
 static int unmap_all(mmap_t ptrs[], size_t len)
 {
 	register int rval=1;
@@ -41,6 +52,7 @@ static int unmap_all(mmap_t ptrs[], size_t len)
 	return rval;
 }
 
+
 static int compare_then_close(const mmap_t * restrict map1, mmap_t map2)
 {
 	register int rval=0;
@@ -60,6 +72,7 @@ static void prep_map(mmap_t* restrict map)
 {
 	if(!set_preload_map(map))
 		fprintf(stderr, "Error: failed to prep map %p (%d), continuing anyway\n", map->ptr, map->fd);
+	else dprintf("prep'd %p (%d)", map->ptr, map->fd);
 }
 
 #ifdef _RUN_THREADED
@@ -198,6 +211,8 @@ int main(int argc, char** argv)
 		dprintf("Children spawned");
 
 		sched_wait(&threads);
+		// Waited, we can now unprep map1
+		unprep_map(&map1, true);
 
 		for (register int i=0;i<nrest;i++) {
 			if(rvals[i]) {

src/map.c

@@ -14,6 +14,8 @@
 
 #define ADVICE DEFAULT_ADVICE | MADV_WILLNEED
 
+#define UNADVICE MADV_NORMAL | MADV_COLD
+
 #include <map.h>
 
 static inline int _map_advise(const mmap_t* restrict map, int adv)
@@ -21,10 +23,19 @@ static inline int _map_advise(const mmap_t* restrict map, int adv)
 	return madvise(map->ptr, map->len, adv);
 }
 
+int unset_preload_map(mmap_t* restrict map, int freeing)
+{
+	if(_map_advise(map, UNADVICE | (freeing ? MADV_DONTNEED : 0)) != 0) {
+		perror("failed to advise kernel to drop mapped page(s)");
+		return 0;
+	}
+	return 1;
+}
+
 int set_preload_map(mmap_t* restrict map)
 {
 	if(_map_advise(map, ADVICE) != 0) {
-		perror("failed to advise kernel about mapped page(s)");
+		perror("failed to advise kernel to preload mapped page(s)");
 		return 0;
 	}
 	return 1;