week8

week08/ex1.txt

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+               total        used        free      shared  buff/cache   available
+Mem:            14Gi       2.4Gi        10Gi        88Mi       2.0Gi        11Gi
+Swap:          8.0Gi          0B       8.0Gi
+Total:          22Gi       2.4Gi        18Gi

week08/ex2.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+
+#define TENMB 10*1024*1024
+
+/* vmstat 1
+ * Inconsistently, probably because timings are not ideal,
+ * but every second free memory decreases by approximately 10MB.
+ * si and so are 0, because swap memory wasn't being used.
+ */
+
+/* top -d 1
+ * By pressing M, top sorts processes by memory usage.
+ * Compared to vmstat, top updates total memory usage
+ * slower. Every second ex2 goes to the top of the 'top'.
+ */
+
+
+int main() {
+    char *p[10];
+    for (int i = 0; i < 10; i++) {
+        p[i] = malloc(TENMB);
+        memset(p[i], 0, TENMB);
+        sleep(1);
+    }
+    for (int i = 0; i < 10; i++) {
+        free(p[i]);
+    }
+}

week08/ex2.sh

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+#!/bin/sh
+
+gcc ex2.c -o ex2
+./ex2 &
+vmstat 1

week08/ex3.sh

@@ -0,0 +1,5 @@
+#!/bin/sh
+
+gcc ex2.c -o ex2
+./ex2 &
+top -d 1

week08/ex4.c

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+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <string.h>
+#include <sys/resource.h>
+
+#define TENMB 10*1024*1024
+
+int main() {
+    char *p[10];
+    for (int i = 0; i < 10; i++) {
+        p[i] = malloc(TENMB);
+        memset(p[i], 0, TENMB);
+        struct rusage usage;
+        if (getrusage(RUSAGE_SELF, &usage) == 0) {
+            printf("Usage: %ldKB\n", usage.ru_maxrss);
+        } else {
+            perror("getrusage");
+            exit(1);
+        }
+        sleep(1);
+    }
+    for (int i = 0; i < 10; i++) {
+        free(p[i]);
+    }
+}

week08/ex4.sh

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+#!/bin/sh
+
+gcc ex4.c -o ex4
+./ex4

week08/ex5.txt

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+Physical address is the actual address in the main memory, whereas virtual address is a logical one that is generated by CPU's MMU.
+Virtual address points to the virtual memory, CPU and OS will take that address and convert it to the physical one to access the actual data.
+All programs running on OS use virtual addresses, since they don't have access to the physical memory.

week08/ex6.txt

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+16-bit address can access 2^16 = 65536 bytes of memory
+8KB is 8192 bytes.
+65536 / 8192 = 8 pages
+Since there are 8 pages, there are 8 table entries.