i think this is a working concurrent logging scheme

48aa9174 · Robert Morris · 71453f72 · 48aa9174 · 48aa9174 · 48aa9174
--- a/bio.c
+++ b/bio.c
@@ -80,6 +80,8 @@ bget(uint dev, uint sector)
  }

  // Not cached; recycle some non-busy and clean buffer.
+  // "clean" because B_DIRTY and !B_BUSY means log.c
+  // hasn't yet committed the changes to the buffer.
  for(b = bcache.head.prev; b != &bcache.head; b = b->prev){
    if((b->flags & B_BUSY) == 0 && (b->flags & B_DIRTY) == 0){
      b->dev = dev;

--- a/log.c
+++ b/log.c
@@ -52,6 +52,10 @@ struct log log;
 static void recover_from_log(void);
 static void commit();

+// statistics, delete eventually XXX.
+static int maxsize;
+static int maxoutstanding;
+
 void
 initlog(void)
 {
@@ -131,10 +135,15 @@ begin_op(void)
  while(1){
    if(log.committing){
      sleep(&log, &log.lock);
+    } else if(log.lh.n + (log.outstanding+1)*MAXOPBLOCKS > LOGSIZE){
+      // this op might exhaust log space; wait for commit.
+      sleep(&log, &log.lock);
    } else {
-      // XXX wait (for a commit) if log is longish.
-      //     need to reserve to avoid over-commit of log space.
      log.outstanding += 1;
+      if(log.outstanding > maxoutstanding){
+        maxoutstanding = log.outstanding;
+        cprintf("%d outstanding\n", log.outstanding);
+      }
      release(&log.lock);
      break;
    }
@@ -155,6 +164,9 @@ end_op(void)
  if(log.outstanding == 0){
    do_commit = 1;
    log.committing = 1;
+  } else {
+    // begin_op() may be waiting for log space.
+    wakeup(&log);
  }
  release(&log.lock);

@@ -208,6 +220,11 @@ log_write(struct buf *b)
  if (i == log.lh.n)
    log.lh.n++;
  b->flags |= B_DIRTY; // XXX prevent eviction
+
+  if(log.lh.n > maxsize){
+    maxsize = log.lh.n;
+    cprintf("log size %d/%d\n", log.lh.n, LOGSIZE);
+  }
 }

 //PAGEBREAK!

--- a/mkfs.c
+++ b/mkfs.c
@@ -13,7 +13,7 @@

 #define static_assert(a, b) do { switch (0) case 0: case (a): ; } while (0)

-int nblocks = 985;
+int nblocks = (995-LOGSIZE);
 int nlog = LOGSIZE;
 int ninodes = 200;
 int size = 1024;

--- a/param.h
+++ b/param.h
@@ -3,10 +3,11 @@
 #define NCPU          8  // maximum number of CPUs
 #define NOFILE       16  // open files per process
 #define NFILE       100  // open files per system
-#define NBUF         10  // size of disk block cache
 #define NINODE       50  // maximum number of active i-nodes
 #define NDEV         10  // maximum major device number
 #define ROOTDEV       1  // device number of file system root disk
 #define MAXARG       32  // max exec arguments
-#define LOGSIZE      10  // max data sectors in on-disk log
+#define MAXOPBLOCKS  10  // max # of blocks any FS op writes
+#define LOGSIZE      (MAXOPBLOCKS*3)  // max data sectors in on-disk log
+#define NBUF         (MAXOPBLOCKS*3)  // size of disk block cache (>= LOGSIZE)

--- a/usertests.c
+++ b/usertests.c
@@ -512,18 +512,20 @@ sharedfd(void)
  }
 }

-// two processes write two different files at the same
+// four processes write different files at the same
 // time, to test block allocation.
 void
-twofiles(void)
+fourfiles(void)
 {
-  int fd, pid, i, j, n, total;
+  int fd, pid, i, j, n, total, pi;
+  char *names[] = { "f0", "f1", "f2", "f3" };
  char *fname;

-  printf(1, "twofiles test\n");
+  printf(1, "fourfiles test\n");

-  unlink("f1");
-  unlink("f2");
+  for(pi = 0; pi < 4; pi++){
+    fname = names[pi];
+    unlink(fname);

    pid = fork();
    if(pid < 0){
@@ -531,32 +533,35 @@ twofiles(void)
      exit();
    }

-  fname = pid ? "f1" : "f2";
+    if(pid == 0){
      fd = open(fname, O_CREATE | O_RDWR);
      if(fd < 0){
        printf(1, "create failed\n");
        exit();
      }
      
-  memset(buf, pid?'p':'c', 512);
+      memset(buf, '0'+pi, 512);
      for(i = 0; i < 12; i++){
        if((n = write(fd, buf, 500)) != 500){
          printf(1, "write failed %d\n", n);
          exit();
        }
      }
-  close(fd);
-  if(pid)
-    wait();
-  else
      exit();
+    }
+  }
+
+  for(pi = 0; pi < 4; pi++){
+    wait();
+  }

  for(i = 0; i < 2; i++){
-    fd = open(i?"f1":"f2", 0);
+    fname = names[i];
+    fd = open(fname, 0);
    total = 0;
    while((n = read(fd, buf, sizeof(buf))) > 0){
      for(j = 0; j < n; j++){
-        if(buf[j] != (i?'p':'c')){
+        if(buf[j] != '0'+i){
          printf(1, "wrong char\n");
          exit();
        }
@@ -568,30 +573,31 @@ twofiles(void)
      printf(1, "wrong length %d\n", total);
      exit();
    }
+    unlink(fname);
  }

-  unlink("f1");
-  unlink("f2");
-
-  printf(1, "twofiles ok\n");
+  printf(1, "fourfiles ok\n");
 }

-// two processes create and delete different files in same directory
+// four processes create and delete different files in same directory
 void
 createdelete(void)
 {
  enum { N = 20 };
-  int pid, i, fd;
+  int pid, i, fd, pi;
  char name[32];

  printf(1, "createdelete test\n");
+
+  for(pi = 0; pi < 4; pi++){
    pid = fork();
    if(pid < 0){
      printf(1, "fork failed\n");
      exit();
    }

-  name[0] = pid ? 'p' : 'c';
+    if(pid == 0){
+      name[0] = 'p' + pi;
      name[2] = '\0';
      for(i = 0; i < N; i++){
        name[1] = '0' + i;
@@ -609,14 +615,18 @@ createdelete(void)
          }
        }
      }
-
-  if(pid==0)
      exit();
-  else
+    }
+  }
+
+  for(pi = 0; pi < 4; pi++){
    wait();
+  }

+  name[0] = name[1] = name[2] = 0;
  for(i = 0; i < N; i++){
-    name[0] = 'p';
+    for(pi = 0; pi < 4; pi++){
+      name[0] = 'p' + pi;
      name[1] = '0' + i;
      fd = open(name, 0);
      if((i == 0 || i >= N/2) && fd < 0){
@@ -628,27 +638,15 @@ createdelete(void)
      }
      if(fd >= 0)
        close(fd);
-
-    name[0] = 'c';
-    name[1] = '0' + i;
-    fd = open(name, 0);
-    if((i == 0 || i >= N/2) && fd < 0){
-      printf(1, "oops createdelete %s didn't exist\n", name);
-      exit();
-    } else if((i >= 1 && i < N/2) && fd >= 0){
-      printf(1, "oops createdelete %s did exist\n", name);
-      exit();
    }
-    if(fd >= 0)
-      close(fd);
  }

  for(i = 0; i < N; i++){
-    name[0] = 'p';
+    for(pi = 0; pi < 4; pi++){
+      name[0] = 'p' + i;
      name[1] = '0' + i;
      unlink(name);
-    name[0] = 'c';
-    unlink(name);
+    }
  }

  printf(1, "createdelete ok\n");
@@ -1716,6 +1714,12 @@ main(int argc, char *argv[])
  }
  close(open("usertests.ran", O_CREATE));

+  createdelete();
+  linkunlink();
+  concreate();
+  fourfiles();
+  sharedfd();
+
  bigargtest();
  bigwrite();
  bigargtest();
@@ -1741,18 +1745,12 @@ main(int argc, char *argv[])
  fourteen();
  bigfile();
  subdir();
-  concreate();
-  linkunlink();
  linktest();
  unlinkread();
-  createdelete();
-  twofiles();
-  sharedfd();
  dirfile();
  iref();
  forktest();
  bigdir(); // slow
-
  exectest();

  exit();