[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>

diff --git a/fs/buffer.c b/fs/buffer.c
index 36c7253..11ca6eb 100644 (file)
--- 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,