pids: increase pid_max based on num_possible_cpus

On a system with a substantial number of processors, the early default
pid_max of 32k will not be enough.  A system with 1664 CPU's, there are
25163 processes started before the login prompt.  It's estimated that with
2048 CPU's we will pass the 32k limit.  With 4096, we'll reach that limit
very early during the boot cycle, and processes would stall waiting for an
available pid.

This patch increases the early maximum number of pids available, and
increases the minimum number of pids that can be set during runtime.

[akpm@linux-foundation.org: fix warnings]
Signed-off-by: Hedi Berriche <hedi@sgi.com>
Signed-off-by: Mike Travis <travis@sgi.com>
Signed-off-by: Robin Holt <holt@sgi.com>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Greg KH <gregkh@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: John Stoffel <john@stoffel.org>
Cc: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/threads.h b/include/linux/threads.h
index 052b12bec8bdabf7a4c8b7af652eb83550c01a93..383ab9592becae78187d8be345e397a6c816765e 100644 (file)
--- a/include/linux/threads.h
+++ b/include/linux/threads.h
@@ -33,4 +33,13 @@
 #define PID_MAX_LIMIT (CONFIG_BASE_SMALL ? PAGE_SIZE * 8 : \
        (sizeof(long) > 4 ? 4 * 1024 * 1024 : PID_MAX_DEFAULT))
 
+/*
+ * Define a minimum number of pids per cpu.  Heuristically based
+ * on original pid max of 32k for 32 cpus.  Also, increase the
+ * minimum settable value for pid_max on the running system based
+ * on similar defaults.  See kernel/pid.c:pidmap_init() for details.
+ */
+#define PIDS_PER_CPU_DEFAULT   1024
+#define PIDS_PER_CPU_MIN       8
+
 #endif

diff --git a/kernel/pid.c b/kernel/pid.c
index aebb30d9c233df40876afa35ef21cc5c306590a1..e9fd8c132d265011e00d75d00e589d83e1d6ce1c 100644 (file)
--- a/kernel/pid.c
+++ b/kernel/pid.c
@@ -513,6 +513,13 @@ void __init pidhash_init(void)
 
 void __init pidmap_init(void)
 {
+       /* bump default and minimum pid_max based on number of cpus */
+       pid_max = min(pid_max_max, max_t(int, pid_max,
+                               PIDS_PER_CPU_DEFAULT * num_possible_cpus()));
+       pid_max_min = max_t(int, pid_max_min,
+                               PIDS_PER_CPU_MIN * num_possible_cpus());
+       pr_info("pid_max: default: %u minimum: %u\n", pid_max, pid_max_min);
+
        init_pid_ns.pidmap[0].page = kzalloc(PAGE_SIZE, GFP_KERNEL);
        /* Reserve PID 0. We never call free_pidmap(0) */
        set_bit(0, init_pid_ns.pidmap[0].page);