Commit 42be35d0 authored by Gilad Ben-Yossef's avatar Gilad Ben-Yossef Committed by Linus Torvalds
Browse files

fs: only send IPI to invalidate LRU BH when needed

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: default avatarGilad Ben-Yossef <>
Acked-by: default avatarPeter Zijlstra <>
Cc: Alexander Viro <>
Signed-off-by: default avatarAndrew Morton <>
Signed-off-by: default avatarLinus Torvalds <>
parent a8364d55
......@@ -1384,10 +1384,23 @@ static void invalidate_bh_lru(void *arg)
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);
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