get rid of NR_OPEN and introduce a sysctl_nr_open

NR_OPEN (historically set to 1024*1024) actually forbids processes to open
more than 1024*1024 handles.

Unfortunatly some production servers hit the not so 'ridiculously high
value' of 1024*1024 file descriptors per process.

Changing NR_OPEN is not considered safe because of vmalloc space potential
exhaust.

This patch introduces a new sysctl (/proc/sys/fs/nr_open) wich defaults to
1024*1024, so that admins can decide to change this limit if their workload
needs it.

[akpm@linux-foundation.org: export it for sparc64]
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 9 insertions, 1 deletions

diff --git a/kernel/sys.c b/kernel/sys.c
index 53de35fc8245..2b8e2daa9d95 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1472,7 +1472,7 @@ asmlinkage long sys_setrlimit(unsigned int resource, struct rlimit __user *rlim)
         if ((new_rlim.rlim_max > old_rlim->rlim_max) &&
             !capable(CAP_SYS_RESOURCE))
                 return -EPERM;
-        if (resource == RLIMIT_NOFILE && new_rlim.rlim_max > NR_OPEN)
+        if (resource == RLIMIT_NOFILE && new_rlim.rlim_max > sysctl_nr_open)
                 return -EPERM;
 
         retval = security_task_setrlimit(resource, &new_rlim);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 5e2ad5bf88e2..86daaa26d120 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1203,6 +1203,14 @@ static struct ctl_table fs_table[] = {
                 .proc_handler   = &proc_dointvec,
         },
         {
+                .ctl_name       = CTL_UNNUMBERED,
+                .procname       = "nr_open",
+                .data           = &sysctl_nr_open,
+                .maxlen         = sizeof(int),
+                .mode           = 0644,
+                .proc_handler   = &proc_dointvec,
+        },
+        {
                 .ctl_name       = FS_DENTRY,
                 .procname       = "dentry-state",
                 .data           = &dentry_stat,