[PATCH v3] Reduce memory waste while managing tcbs

[Nahim El Atmani]

From: Nahim El Atmani <naam at lse.epita.fr>

* strace.c: alloctcb() when no tcbs are available (first call and subsequent
calls when tcbtab is full) call expand_tcbtab(). Now, expand_tcbtab() allocate
the minimum required amount of memory to create the tcbtab if needed and expend
otherwise instead of relying on the preallocation of a large amount of tcbs
and expand if needed.

Signed-off-by: Nahim El Atmani <nahim+dev at naam.me>
Reviewed-By: Gabriel Laskar <gabriel at lse.epita.fr>
Reported-by: haris iqbal <haris.phnx at gmail.com>

---
 strace.c | 31 ++++++++++++++++---------------
 1 file changed, 16 insertions(+), 15 deletions(-)

diff --git a/strace.c b/strace.c
index 785cc60..e97fe9e 100644
--- a/strace.c
+++ b/strace.c
@@ -691,16 +691,26 @@ newoutf(struct tcb *tcp)
 static void
 expand_tcbtab(void)
 {
-	/* Allocate some more TCBs and expand the table.
+	/* Allocate some (more) TCBs (and expand the table).
 	   We don't want to relocate the TCBs because our
 	   callers have pointers and it would be a pain.
 	   So tcbtab is a table of pointers.  Since we never
 	   free the TCBs, we allocate a single chunk of many.  */
-	unsigned int i = tcbtabsize;
-	struct tcb *newtcbs = xcalloc(tcbtabsize, sizeof(newtcbs[0]));
-	struct tcb **newtab = xreallocarray(tcbtab, tcbtabsize * 2,
-					    sizeof(tcbtab[0]));
-	tcbtabsize *= 2;
+	unsigned int i, new_tcbtabsize, alloc_tcbtabsize;
+	struct tcb *newtcbs;
+	struct tcb **newtab;
+
+	if (tcbtabsize) {
+		alloc_tcbtabsize = tcbtabsize;
+		new_tcbtabsize = tcbtabsize * 2;
+	} else {
+		new_tcbtabsize = alloc_tcbtabsize = 1;
+	}
+
+	i = tcbtabsize;
+	newtcbs = xcalloc(alloc_tcbtabsize, sizeof(newtcbs[0]));
+	newtab = xreallocarray(tcbtab, new_tcbtabsize, sizeof(tcbtab[0]));
+	tcbtabsize = new_tcbtabsize;
 	tcbtab = newtab;
 	while (i < tcbtabsize)
 		tcbtab[i++] = newtcbs++;
@@ -1484,10 +1494,8 @@ get_os_release(void)
 static void ATTRIBUTE_NOINLINE
 init(int argc, char *argv[])
 {
-	struct tcb *tcp;
 	int c, i;
 	int optF = 0;
-	unsigned int tcbi;
 	struct sigaction sa;

 	progname = argv[0] ? argv[0] : "strace";
@@ -1503,13 +1511,6 @@ init(int argc, char *argv[])

 	os_release = get_os_release();

-	/* Allocate the initial tcbtab.  */
-	tcbtabsize = argc;	/* Surely enough for all -p args.  */
-	tcbtab = xcalloc(tcbtabsize, sizeof(tcbtab[0]));
-	tcp = xcalloc(tcbtabsize, sizeof(*tcp));
-	for (tcbi = 0; tcbi < tcbtabsize; tcbi++)
-		tcbtab[tcbi] = tcp++;
-
 	shared_log = stderr;
 	set_sortby(DEFAULT_SORTBY);
 	set_personality(DEFAULT_PERSONALITY);
-- 
Nahim El Atmani <nahim+dev at naam.me>
http://naam.me/