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>

1 files changed, 5 insertions, 3 deletions

diff --git a/fs/file.c b/fs/file.c
index c5575de01113..5110acb1c9ef 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -24,6 +24,8 @@ struct fdtable_defer {
         struct fdtable *next;
 };
 
+int sysctl_nr_open __read_mostly = 1024*1024;
+
 /*
  * We use this list to defer free fdtables that have vmalloced
  * sets/arrays. By keeping a per-cpu list, we avoid having to embed
@@ -147,8 +149,8 @@ static struct fdtable * alloc_fdtable(unsigned int nr)
         nr /= (1024 / sizeof(struct file *));
         nr = roundup_pow_of_two(nr + 1);
         nr *= (1024 / sizeof(struct file *));
-        if (nr > NR_OPEN)
-                nr = NR_OPEN;
+        if (nr > sysctl_nr_open)
+                nr = sysctl_nr_open;
 
         fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL);
         if (!fdt)
@@ -233,7 +235,7 @@ int expand_files(struct files_struct *files, int nr)
         if (nr < fdt->max_fds)
                 return 0;
         /* Can we expand? */
-        if (nr >= NR_OPEN)
+        if (nr >= sysctl_nr_open)
                 return -EMFILE;
 
         /* All good, so we try */