Add fill mode in memtool

JOURNAL.md

@@ -1072,3 +1072,22 @@ and see if it has any effect?
     iter=292 nblocks=229 allocated=58599K (A)
 
 Has changed, but not much.
+
+    aaaiter=291 nblocks=228 allocated=58480K (A)
+    allocating...
+    filling...
+    aaaaaaaaiter=292 nblocks=229 allocated=58599K (A)
+    allocating...
+    aafilling...
+
+It seems to be getting stuck in the filling phase. Can we trace it down with
+ftrace? It should be generating page faults.
+
+### 2024-07-10
+
+So, if we manage to crash in the filling phase, we can further pinpoint the
+issue and remove any effect of `malloc()`. It would be only related to a page
+fault and the MMU at this point.
+
+Let's make a much simpler program that only allocates once a buffer of N bytes
+and then begins filling it, printing the progress in the output.

lagarto-ox.nix

@@ -88,7 +88,8 @@
 
         export PATH=${config.system.build.extraUtils}/bin
 
-        memtool $((512 * 1024))
+        #memtool chain $((512 * 1024))
+        memtool fill $((512 * 1024 * 1024))
 
         # Unlikely to reach this point
         exec /init

memtool.c

@@ -6,9 +6,14 @@
  * stress the virtual memory, in a crude attempt to reproduce the hangs
  * that we were observing while booting NixOS. */
 
+/* Changelog:
+ *   v0.0.1 (2024-07-10): Start version with "chain" and "fill" tests.
+ */
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <stdint.h>
+#include <string.h>
 
 #define MAX_SIZE (1024L * 1024L)
 
@@ -18,17 +23,19 @@ struct block {
 	uint32_t data[];
 };
 
-struct block *front = NULL;
-struct block *tail = NULL;
-long nblocks = 0;
-long nbytes = 0;
-long maxsize = MAX_SIZE;
+struct chain {
+	struct block *front;
+	struct block *tail;
+	long maxsize;
+	long nbytes;
+	long nblocks;
+};
 
 static int
-allocate(void)
+allocate(struct chain *chain)
 {
 	/* Constraint the number of elements based on the maxsize */
-	long maxn = maxsize / sizeof(uint32_t);
+	long maxn = chain->maxsize / sizeof(uint32_t);
 	long n = (long) rand() % maxn;
 
 	size_t size = sizeof(struct block) + n * sizeof(uint32_t);
@@ -50,38 +57,38 @@ allocate(void)
 		b->data[i] = rand();
 
 	/* Add it to the chain */
-	if (tail)
-		tail->next = b;
+	if (chain->tail)
+		chain->tail->next = b;
 
-	tail = b;
+	chain->tail = b;
 
 	/* And to the front if it is the first */
-	if (!front)
-		front = b;
+	if (!chain->front)
+		chain->front = b;
 
-	nblocks++;
-	nbytes += size;
+	chain->nblocks++;
+	chain->nbytes += size;
 
 	return 0;
 }
 
 static int
-deallocate(void)
+deallocate(struct chain *chain)
 {
 	/* May run out of blocks */
-	if (!front)
+	if (!chain->front)
 		return -1;
 
-	struct block *b = front;
+	struct block *b = chain->front;
 
-	front = b->next;
+	chain->front = b->next;
 
 	/* Last block */
-	if (tail == b)
-		tail = NULL;
+	if (chain->tail == b)
+		chain->tail = NULL;
 
-	nblocks--;
-	nbytes -= b->size;
+	chain->nblocks--;
+	chain->nbytes -= b->size;
 
 	printf("deallocating...\n");
 	free(b);
@@ -90,8 +97,18 @@ deallocate(void)
 }
 
 static void
-torture(void)
+do_chain(int argc, char *argv[])
 {
+	struct chain chain = {0};
+
+	/* Default 1 MiB */
+	chain.maxsize = 1024L * 1024L;
+
+	if (argc > 0)
+		chain.maxsize = atol(argv[0]);
+
+	printf("mode chain: maxsize=%ldK\n", chain.maxsize / 1024);
+
 	srand(123);
 
 	for (long iter = 0; ; iter++) {
@@ -100,31 +117,98 @@ torture(void)
 		int ret = 0;
 		char c;
 		if (is_alloc) {
-			if (allocate() == 0)
+			if (allocate(&chain) == 0)
 				c = 'A';
 			else
 				c = '-';
 		} else {
-			if (deallocate() == 0)
+			if (deallocate(&chain) == 0)
 				c = 'D';
 			else
 				c = '-';
 		}
 
 		printf("iter=%ld nblocks=%ld allocated=%ldK (%c)\n",
-				iter, nblocks, nbytes / 1024,
+				iter, chain.nblocks, chain.nbytes / 1024,
 				c);
 	}
 }
 
+static void
+do_fill(int argc, char *argv[])
+{
+	/* Default: 256 MiB */
+	long nbytes = 256L * 1024L * 1024L;
+
+	if (argc > 0)
+		nbytes = atol(argv[0]);
+
+	long n = nbytes / sizeof(int);
+
+	printf("mode fill: nbytes=%ldM, n=%ld\n",
+			nbytes / (1024L * 1024L), n);
+
+	int *buf = malloc(nbytes);
+
+	if (!buf) {
+		perror("malloc failed");
+		exit(1);
+	}
+
+	for (long i = 0; i < n; i++) {
+		buf[i] = i;
+		if ((i % (1024L * 1024L)) == 0)
+			printf("written=%ldK, addr=%p OK\n",
+					i * sizeof(int) / 1024L,
+					&buf[i]);
+	}
+
+	free(buf);
+
+	printf("fill test OK\n");
+}
+
+static void
+usage(void)
+{
+	printf(
+"Usage: memtool <command> [<options>...]\n"
+"\n"
+"Available commands:\n"
+"  chain [<maxsize>]\n"
+"        Creates a chain of blocks of random size, each up to maxsize\n"
+"        or 1MiB if not given. Blocks are freed with 10% probability\n"
+"        starting from the oldest.\n"
+"\n"
+"  fill [<size>]\n"
+"        Allocates a vector of the given size (or 256 MiB if not given)\n"
+"        and initializes it with a increasing value per element.\n"
+"\n");
+
+	exit(1);
+}
+
 int main(int argc, char *argv[])
 {
-	if (argc > 1)
-		maxsize = atol(argv[1]);
+	printf("memtool v0.0.1 - Rodrigo Arias Mallo <rodrigo.arias@bsc.es>\n");
 
-	printf("memtool v1.0.0 maxsize=%ldK\n", maxsize / 1024);
+	if (argc < 2)
+		usage();
 
-	torture();
+	/* Skip program name */
+	argc--; argv++;
+
+	const char *mode = argv[0];
+
+	/* Skip mode */
+	argc--; argv++;
+
+	if (strcmp(mode, "chain") == 0)
+		do_chain(argc, argv);
+	else if (strcmp(mode, "fill") == 0)
+		do_fill(argc, argv);
+	else
+		usage();
 
 	return 0;
 }