Re: [PATCH] flexmmap: optimise mmap_base gap for hard limited stack

[Utz Lehmann <lkml@de.tecosim.com>]

Ulrich Drepper [drepper@redhat.com] wrote:
> > A check for CAP_SYS_RESOURCE can be added. But i dont think it's worth.
> 
> It is needed.  Otherwise how do you allow increasing the stack size
> again once it has been limited?  I've no problem with using the smallest
> reserved stack region with !CAP_SYS_RESOURCE, but otherwise the existing
> method should be used.

I made that change. The following patch only reduce the gap when the
application can not extend the stack space anyway (hard limited stack &&
!CAP_SYS_RESOURCE). All other cases stay unchanged except for the 1 MB hole
for soft limited stacks >128 MB.

It gave a nice way for making most of the default 128 MB gap usable for
applications. Just run them with a hard stack limit.

Now i can allocate more than 3.8GiB in one chunk on x86 (this patch +
exec-shield + 4g/4g + ulimit -H -s 8192).


Signed-off-by: Utz Lehmann <lkml@de.tecosim.com>

diff -Nrup linux-2.6.9-rc2/arch/i386/mm/mmap.c linux-2.6.9-rc2-gap4/arch/i386/mm/mmap.c
--- linux-2.6.9-rc2/arch/i386/mm/mmap.c	2004-09-16 11:18:15.363366420 +0200
+++ linux-2.6.9-rc2-gap4/arch/i386/mm/mmap.c	2004-09-17 12:14:16.734968291 +0200
@@ -30,10 +30,13 @@
 /*
  * Top of mmap area (just below the process stack).
  *
- * Leave an at least ~128 MB hole.
+ * Leave an at least 1 MB hole between stack and mmap_base.
+ * Leave an at least 128 MB gap between TASK_SIZE and mmap_base with a
+ * soft rlimit stack.
  */
-#define MIN_GAP (128*1024*1024)
-#define MAX_GAP (TASK_SIZE/6*5)
+#define MIN_HOLE (1*1024*1024)
+#define MIN_GAP (128*1024*1024 - MIN_HOLE)
+#define MAX_GAP (TASK_SIZE/6*5 - MIN_HOLE)
 
 static inline unsigned long mmap_base(struct mm_struct *mm)
 {
@@ -43,8 +46,11 @@ static inline unsigned long mmap_base(st
 		gap = MIN_GAP;
 	else if (gap > MAX_GAP)
 		gap = MAX_GAP;
+	if ((gap > current->rlim[RLIMIT_STACK].rlim_max) &&
+			!capable(CAP_SYS_RESOURCE))
+		gap = current->rlim[RLIMIT_STACK].rlim_max;
 
-	return TASK_SIZE - (gap & PAGE_MASK);
+	return TASK_SIZE - ((gap + MIN_HOLE) & PAGE_MASK);
 }
 
 /*
diff -Nrup linux-2.6.9-rc2/arch/ppc64/mm/mmap.c linux-2.6.9-rc2-gap4/arch/ppc64/mm/mmap.c
--- linux-2.6.9-rc2/arch/ppc64/mm/mmap.c	2004-09-16 11:18:19.760799910 +0200
+++ linux-2.6.9-rc2-gap4/arch/ppc64/mm/mmap.c	2004-09-17 12:15:05.572696938 +0200
@@ -30,10 +30,13 @@
 /*
  * Top of mmap area (just below the process stack).
  *
- * Leave an at least ~128 MB hole.
+ * Leave an at least 1 MB hole between stack and mmap_base.
+ * Leave an at least 128 MB gap between TASK_SIZE and mmap_base with a
+ * soft rlimit stack.
  */
-#define MIN_GAP (128*1024*1024)
-#define MAX_GAP (TASK_SIZE/6*5)
+#define MIN_HOLE (1*1024*1024)
+#define MIN_GAP (128*1024*1024 - MIN_HOLE)
+#define MAX_GAP (TASK_SIZE/6*5 - MIN_HOLE)
 
 static inline unsigned long mmap_base(void)
 {
@@ -43,8 +46,11 @@ static inline unsigned long mmap_base(vo
 		gap = MIN_GAP;
 	else if (gap > MAX_GAP)
 		gap = MAX_GAP;
+	if ((gap > current->rlim[RLIMIT_STACK].rlim_max) &&
+			!capable(CAP_SYS_RESOURCE))
+		gap = current->rlim[RLIMIT_STACK].rlim_max;
 
-	return TASK_SIZE - (gap & PAGE_MASK);
+	return TASK_SIZE - ((gap + MIN_HOLE) & PAGE_MASK);
 }
 
 static inline int mmap_is_legacy(void)
diff -Nrup linux-2.6.9-rc2/arch/s390/mm/mmap.c linux-2.6.9-rc2-gap4/arch/s390/mm/mmap.c
--- linux-2.6.9-rc2/arch/s390/mm/mmap.c	2004-09-16 11:18:19.855787673 +0200
+++ linux-2.6.9-rc2-gap4/arch/s390/mm/mmap.c	2004-09-17 12:15:23.054452086 +0200
@@ -30,10 +30,13 @@
 /*
  * Top of mmap area (just below the process stack).
  *
- * Leave an at least ~128 MB hole.
+ * Leave an at least 1 MB hole between stack and mmap_base.
+ * Leave an at least 128 MB gap between TASK_SIZE and mmap_base with a
+ * soft rlimit stack.
  */
-#define MIN_GAP (128*1024*1024)
-#define MAX_GAP (TASK_SIZE/6*5)
+#define MIN_HOLE (1*1024*1024)
+#define MIN_GAP (128*1024*1024 - MIN_HOLE)
+#define MAX_GAP (TASK_SIZE/6*5 - MIN_HOLE)
 
 static inline unsigned long mmap_base(void)
 {
@@ -43,8 +46,11 @@ static inline unsigned long mmap_base(vo
 		gap = MIN_GAP;
 	else if (gap > MAX_GAP)
 		gap = MAX_GAP;
+	if ((gap > current->rlim[RLIMIT_STACK].rlim_max) &&
+			!capable(CAP_SYS_RESOURCE))
+		gap = current->rlim[RLIMIT_STACK].rlim_max;
 
-	return TASK_SIZE - (gap & PAGE_MASK);
+	return TASK_SIZE - ((gap + MIN_HOLE) & PAGE_MASK);
 }
 
 static inline int mmap_is_legacy(void)