In several code paths, such as when unmounting a file system (but not only) we send an IPI to ask each cpu to invalidate its local LRU BHs. For multi-cores systems that have many cpus that may not have any LRU BH because they are idle or because they have not performed any file system accesses since last invalidation (e.g. CPU crunching on high perfomance computing nodes that write results to shared memory or only using filesystems that do not use the bh layer.) This can lead to loss of performance each time someone switches the KVM (the virtual keyboard and screen type, not the hypervisor) if it has a USB storage stuck in. This patch attempts to only send an IPI to cpus that have LRU BH. Signed-off-by: Gilad Ben-Yossef <gilad@xxxxxxxxxxxxx> CC: Christoph Lameter <cl@xxxxxxxxx> CC: Chris Metcalf <cmetcalf@xxxxxxxxxx> CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> CC: Frederic Weisbecker <fweisbec@xxxxxxxxx> CC: Russell King <linux@xxxxxxxxxxxxxxxx> CC: linux-mm@xxxxxxxxx CC: Pekka Enberg <penberg@xxxxxxxxxx> CC: Matt Mackall <mpm@xxxxxxxxxxx> CC: Sasha Levin <levinsasha928@xxxxxxxxx> CC: Rik van Riel <riel@xxxxxxxxxx> CC: Andi Kleen <andi@xxxxxxxxxxxxxx> CC: Mel Gorman <mel@xxxxxxxxx> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> CC: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx> CC: linux-fsdevel@xxxxxxxxxxxxxxx CC: Avi Kivity <avi@xxxxxxxxxx> CC: Michal Nazarewicz <mina86@xxxxxxxxxx> CC: Kosaki Motohiro <kosaki.motohiro@xxxxxxxxx> CC: Milton Miller <miltonm@xxxxxxx> --- fs/buffer.c | 15 ++++++++++++++- 1 files changed, 14 insertions(+), 1 deletions(-) diff --git a/fs/buffer.c b/fs/buffer.c index 1a30db7..baa075e 100644 --- a/fs/buffer.c +++ b/fs/buffer.c @@ -1384,10 +1384,23 @@ static void invalidate_bh_lru(void *arg) } put_cpu_var(bh_lrus); } + +static bool has_bh_in_lru(int cpu, void *dummy) +{ + struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu); + int i; + for (i = 0; i < BH_LRU_SIZE; i++) { + if (b->bhs[i]) + return 1; + } + + return 0; +} + void invalidate_bh_lrus(void) { - on_each_cpu(invalidate_bh_lru, NULL, 1); + on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1, GFP_KERNEL); } EXPORT_SYMBOL_GPL(invalidate_bh_lrus); -- 1.7.0.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>