[PATCH] HOTPLUG_CPU: avoid hitting too many cachelines in recalc_bh_state()

Instead of using for_each_cpu(i), we can use for_each_online_cpu(i).

When a CPU goes offline (ie removed from online map), it might have a non
null bh_accounting.nr, so this patch adds a transfer of this counter to an
online CPU counter.

We already have a hotcpu_notifier, (function buffer_cpu_notify()), where we
can do this bh_accounting.

Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 4 insertions, 1 deletions

diff --git a/fs/buffer.c b/fs/buffer.c
index 36c7253bea72..11ca6eb46a33 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -3078,7 +3078,7 @@ static void recalc_bh_state(void)
         if (__get_cpu_var(bh_accounting).ratelimit++ < 4096)
                 return;
         __get_cpu_var(bh_accounting).ratelimit = 0;
-        for_each_cpu(i)
+        for_each_online_cpu(i)
                 tot += per_cpu(bh_accounting, i).nr;
         buffer_heads_over_limit = (tot > max_buffer_heads);
 }
@@ -3127,6 +3127,9 @@ static void buffer_exit_cpu(int cpu)
                 brelse(b->bhs[i]);
                 b->bhs[i] = NULL;
         }
+        get_cpu_var(bh_accounting).nr += per_cpu(bh_accounting, cpu).nr;
+        per_cpu(bh_accounting, cpu).nr = 0;
+        put_cpu_var(bh_accounting);
 }
 
 static int buffer_cpu_notify(struct notifier_block *self,