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Subject[PATCH 04/10] x86,mm: use on_each_cpu_cond for TLB flushes
Date
Instead of open coding bitmap magic, use on_each_cpu_cond
to determine which CPUs to send TLB flush IPIs to.

This might be a little bit slower than examining the bitmaps,
but it should be a lot easier to maintain in the long run.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Rik van Riel <riel@surriel.com>
---
arch/x86/mm/tlb.c | 75 +++++++++++--------------------------------------------
1 file changed, 15 insertions(+), 60 deletions(-)

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 5321e02c4e09..671cc66df801 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -582,12 +582,19 @@ static void flush_tlb_func_remote(void *info)
flush_tlb_func_common(f, false, TLB_REMOTE_SHOOTDOWN);
}

+static bool tlb_is_lazy(int cpu, void *data)
+{
+ return per_cpu(cpu_tlbstate.is_lazy, cpu);
+}
+
+static bool tlb_is_not_lazy(int cpu, void *data)
+{
+ return !per_cpu(cpu_tlbstate.is_lazy, cpu);
+}
+
void native_flush_tlb_others(const struct cpumask *cpumask,
const struct flush_tlb_info *info)
{
- cpumask_var_t lazymask;
- unsigned int cpu;
-
count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
if (info->end == TLB_FLUSH_ALL)
trace_tlb_flush(TLB_REMOTE_SEND_IPI, TLB_FLUSH_ALL);
@@ -596,6 +603,7 @@ void native_flush_tlb_others(const struct cpumask *cpumask,
(info->end - info->start) >> PAGE_SHIFT);

if (is_uv_system()) {
+ unsigned int cpu;
/*
* This whole special case is confused. UV has a "Broadcast
* Assist Unit", which seems to be a fancy way to send IPIs.
@@ -619,28 +627,8 @@ void native_flush_tlb_others(const struct cpumask *cpumask,
return;
}

- /*
- * A temporary cpumask is used in order to skip sending IPIs
- * to CPUs in lazy TLB state, while keeping them in mm_cpumask(mm).
- * If the allocation fails, simply IPI every CPU in mm_cpumask.
- */
- if (!alloc_cpumask_var(&lazymask, GFP_ATOMIC)) {
- smp_call_function_many(cpumask, flush_tlb_func_remote,
- (void *)info, 1);
- return;
- }
-
- cpumask_copy(lazymask, cpumask);
-
- for_each_cpu(cpu, lazymask) {
- if (per_cpu(cpu_tlbstate.is_lazy, cpu))
- cpumask_clear_cpu(cpu, lazymask);
- }
-
- smp_call_function_many(lazymask, flush_tlb_func_remote,
- (void *)info, 1);
-
- free_cpumask_var(lazymask);
+ on_each_cpu_cond_mask(tlb_is_not_lazy, flush_tlb_func_remote,
+ (void *)info, 1, GFP_ATOMIC, cpumask);
}

/*
@@ -709,50 +697,17 @@ void tlb_flush_remove_tables_local(void *arg)
}
}

-static void mm_fill_lazy_tlb_cpu_mask(struct mm_struct *mm,
- struct cpumask *lazy_cpus)
-{
- int cpu;
-
- for_each_cpu(cpu, mm_cpumask(mm)) {
- if (!per_cpu(cpu_tlbstate.is_lazy, cpu))
- cpumask_set_cpu(cpu, lazy_cpus);
- }
-}
-
void tlb_flush_remove_tables(struct mm_struct *mm)
{
int cpu = get_cpu();
- cpumask_var_t lazy_cpus;

if (cpumask_any_but(mm_cpumask(mm), cpu) >= nr_cpu_ids) {
put_cpu();
return;
}

- if (!zalloc_cpumask_var(&lazy_cpus, GFP_ATOMIC)) {
- /*
- * If the cpumask allocation fails, do a brute force flush
- * on all the CPUs that have this mm loaded.
- */
- smp_call_function_many(mm_cpumask(mm),
- tlb_flush_remove_tables_local, (void *)mm, 1);
- put_cpu();
- return;
- }
-
- /*
- * CPUs with !is_lazy either received a TLB flush IPI while the user
- * pages in this address range were unmapped, or have context switched
- * and reloaded %CR3 since then.
- *
- * Shootdown IPIs at page table freeing time only need to be sent to
- * CPUs that may have out of date TLB contents.
- */
- mm_fill_lazy_tlb_cpu_mask(mm, lazy_cpus);
- smp_call_function_many(lazy_cpus,
- tlb_flush_remove_tables_local, (void *)mm, 1);
- free_cpumask_var(lazy_cpus);
+ on_each_cpu_cond_mask(tlb_is_lazy, tlb_flush_remove_tables_local,
+ (void *)mm, 1, GFP_ATOMIC, mm_cpumask(mm));
put_cpu();
}

--
2.14.4
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