![Mel Gorman](/assets/img/avatar_default.png)
When unmapping pages it is necessary to flush the TLB. If that page was accessed by another CPU then an IPI is used to flush the remote CPU. That is a lot of IPIs if kswapd is scanning and unmapping >100K pages per second. There already is a window between when a page is unmapped and when it is TLB flushed. This series increases the window so multiple pages can be flushed using a single IPI. This should be safe or the kernel is hosed already. Patch 1 simply made the rest of the series easier to write as ftrace could identify all the senders of TLB flush IPIS. Patch 2 tracks what CPUs potentially map a PFN and then sends an IPI to flush the entire TLB. Patch 3 tracks when there potentially are writable TLB entries that need to be batched differently Patch 4 increases SWAP_CLUSTER_MAX to further batch flushes The performance impact is documented in the changelogs but in the optimistic case on a 4-socket machine the full series reduces interrupts from 900K interrupts/second to 60K interrupts/second. This patch (of 4): It is easy to trace when an IPI is received to flush a TLB but harder to detect what event sent it. This patch makes it easy to identify the source of IPIs being transmitted for TLB flushes on x86. Signed-off-by: Mel Gorman <mgorman@suse.de> Reviewed-by: Rik van Riel <riel@redhat.com> Reviewed-by: Dave Hansen <dave.hansen@intel.com> Acked-by: Ingo Molnar <mingo@kernel.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
327 lines
8.8 KiB
C
327 lines
8.8 KiB
C
#include <linux/init.h>
|
|
|
|
#include <linux/mm.h>
|
|
#include <linux/spinlock.h>
|
|
#include <linux/smp.h>
|
|
#include <linux/interrupt.h>
|
|
#include <linux/module.h>
|
|
#include <linux/cpu.h>
|
|
|
|
#include <asm/tlbflush.h>
|
|
#include <asm/mmu_context.h>
|
|
#include <asm/cache.h>
|
|
#include <asm/apic.h>
|
|
#include <asm/uv/uv.h>
|
|
#include <linux/debugfs.h>
|
|
|
|
/*
|
|
* Smarter SMP flushing macros.
|
|
* c/o Linus Torvalds.
|
|
*
|
|
* These mean you can really definitely utterly forget about
|
|
* writing to user space from interrupts. (Its not allowed anyway).
|
|
*
|
|
* Optimizations Manfred Spraul <manfred@colorfullife.com>
|
|
*
|
|
* More scalable flush, from Andi Kleen
|
|
*
|
|
* Implement flush IPI by CALL_FUNCTION_VECTOR, Alex Shi
|
|
*/
|
|
|
|
struct flush_tlb_info {
|
|
struct mm_struct *flush_mm;
|
|
unsigned long flush_start;
|
|
unsigned long flush_end;
|
|
};
|
|
|
|
/*
|
|
* We cannot call mmdrop() because we are in interrupt context,
|
|
* instead update mm->cpu_vm_mask.
|
|
*/
|
|
void leave_mm(int cpu)
|
|
{
|
|
struct mm_struct *active_mm = this_cpu_read(cpu_tlbstate.active_mm);
|
|
if (this_cpu_read(cpu_tlbstate.state) == TLBSTATE_OK)
|
|
BUG();
|
|
if (cpumask_test_cpu(cpu, mm_cpumask(active_mm))) {
|
|
cpumask_clear_cpu(cpu, mm_cpumask(active_mm));
|
|
load_cr3(swapper_pg_dir);
|
|
/*
|
|
* This gets called in the idle path where RCU
|
|
* functions differently. Tracing normally
|
|
* uses RCU, so we have to call the tracepoint
|
|
* specially here.
|
|
*/
|
|
trace_tlb_flush_rcuidle(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL);
|
|
}
|
|
}
|
|
EXPORT_SYMBOL_GPL(leave_mm);
|
|
|
|
/*
|
|
* The flush IPI assumes that a thread switch happens in this order:
|
|
* [cpu0: the cpu that switches]
|
|
* 1) switch_mm() either 1a) or 1b)
|
|
* 1a) thread switch to a different mm
|
|
* 1a1) set cpu_tlbstate to TLBSTATE_OK
|
|
* Now the tlb flush NMI handler flush_tlb_func won't call leave_mm
|
|
* if cpu0 was in lazy tlb mode.
|
|
* 1a2) update cpu active_mm
|
|
* Now cpu0 accepts tlb flushes for the new mm.
|
|
* 1a3) cpu_set(cpu, new_mm->cpu_vm_mask);
|
|
* Now the other cpus will send tlb flush ipis.
|
|
* 1a4) change cr3.
|
|
* 1a5) cpu_clear(cpu, old_mm->cpu_vm_mask);
|
|
* Stop ipi delivery for the old mm. This is not synchronized with
|
|
* the other cpus, but flush_tlb_func ignore flush ipis for the wrong
|
|
* mm, and in the worst case we perform a superfluous tlb flush.
|
|
* 1b) thread switch without mm change
|
|
* cpu active_mm is correct, cpu0 already handles flush ipis.
|
|
* 1b1) set cpu_tlbstate to TLBSTATE_OK
|
|
* 1b2) test_and_set the cpu bit in cpu_vm_mask.
|
|
* Atomically set the bit [other cpus will start sending flush ipis],
|
|
* and test the bit.
|
|
* 1b3) if the bit was 0: leave_mm was called, flush the tlb.
|
|
* 2) switch %%esp, ie current
|
|
*
|
|
* The interrupt must handle 2 special cases:
|
|
* - cr3 is changed before %%esp, ie. it cannot use current->{active_,}mm.
|
|
* - the cpu performs speculative tlb reads, i.e. even if the cpu only
|
|
* runs in kernel space, the cpu could load tlb entries for user space
|
|
* pages.
|
|
*
|
|
* The good news is that cpu_tlbstate is local to each cpu, no
|
|
* write/read ordering problems.
|
|
*/
|
|
|
|
/*
|
|
* TLB flush funcation:
|
|
* 1) Flush the tlb entries if the cpu uses the mm that's being flushed.
|
|
* 2) Leave the mm if we are in the lazy tlb mode.
|
|
*/
|
|
static void flush_tlb_func(void *info)
|
|
{
|
|
struct flush_tlb_info *f = info;
|
|
|
|
inc_irq_stat(irq_tlb_count);
|
|
|
|
if (f->flush_mm != this_cpu_read(cpu_tlbstate.active_mm))
|
|
return;
|
|
if (!f->flush_end)
|
|
f->flush_end = f->flush_start + PAGE_SIZE;
|
|
|
|
count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
|
|
if (this_cpu_read(cpu_tlbstate.state) == TLBSTATE_OK) {
|
|
if (f->flush_end == TLB_FLUSH_ALL) {
|
|
local_flush_tlb();
|
|
trace_tlb_flush(TLB_REMOTE_SHOOTDOWN, TLB_FLUSH_ALL);
|
|
} else {
|
|
unsigned long addr;
|
|
unsigned long nr_pages =
|
|
(f->flush_end - f->flush_start) / PAGE_SIZE;
|
|
addr = f->flush_start;
|
|
while (addr < f->flush_end) {
|
|
__flush_tlb_single(addr);
|
|
addr += PAGE_SIZE;
|
|
}
|
|
trace_tlb_flush(TLB_REMOTE_SHOOTDOWN, nr_pages);
|
|
}
|
|
} else
|
|
leave_mm(smp_processor_id());
|
|
|
|
}
|
|
|
|
void native_flush_tlb_others(const struct cpumask *cpumask,
|
|
struct mm_struct *mm, unsigned long start,
|
|
unsigned long end)
|
|
{
|
|
struct flush_tlb_info info;
|
|
info.flush_mm = mm;
|
|
info.flush_start = start;
|
|
info.flush_end = end;
|
|
|
|
count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
|
|
trace_tlb_flush(TLB_REMOTE_SEND_IPI, end - start);
|
|
if (is_uv_system()) {
|
|
unsigned int cpu;
|
|
|
|
cpu = smp_processor_id();
|
|
cpumask = uv_flush_tlb_others(cpumask, mm, start, end, cpu);
|
|
if (cpumask)
|
|
smp_call_function_many(cpumask, flush_tlb_func,
|
|
&info, 1);
|
|
return;
|
|
}
|
|
smp_call_function_many(cpumask, flush_tlb_func, &info, 1);
|
|
}
|
|
|
|
void flush_tlb_current_task(void)
|
|
{
|
|
struct mm_struct *mm = current->mm;
|
|
|
|
preempt_disable();
|
|
|
|
count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
|
|
local_flush_tlb();
|
|
trace_tlb_flush(TLB_LOCAL_SHOOTDOWN, TLB_FLUSH_ALL);
|
|
if (cpumask_any_but(mm_cpumask(mm), smp_processor_id()) < nr_cpu_ids)
|
|
flush_tlb_others(mm_cpumask(mm), mm, 0UL, TLB_FLUSH_ALL);
|
|
preempt_enable();
|
|
}
|
|
|
|
/*
|
|
* See Documentation/x86/tlb.txt for details. We choose 33
|
|
* because it is large enough to cover the vast majority (at
|
|
* least 95%) of allocations, and is small enough that we are
|
|
* confident it will not cause too much overhead. Each single
|
|
* flush is about 100 ns, so this caps the maximum overhead at
|
|
* _about_ 3,000 ns.
|
|
*
|
|
* This is in units of pages.
|
|
*/
|
|
static unsigned long tlb_single_page_flush_ceiling __read_mostly = 33;
|
|
|
|
void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
|
|
unsigned long end, unsigned long vmflag)
|
|
{
|
|
unsigned long addr;
|
|
/* do a global flush by default */
|
|
unsigned long base_pages_to_flush = TLB_FLUSH_ALL;
|
|
|
|
preempt_disable();
|
|
if (current->active_mm != mm)
|
|
goto out;
|
|
|
|
if (!current->mm) {
|
|
leave_mm(smp_processor_id());
|
|
goto out;
|
|
}
|
|
|
|
if ((end != TLB_FLUSH_ALL) && !(vmflag & VM_HUGETLB))
|
|
base_pages_to_flush = (end - start) >> PAGE_SHIFT;
|
|
|
|
if (base_pages_to_flush > tlb_single_page_flush_ceiling) {
|
|
base_pages_to_flush = TLB_FLUSH_ALL;
|
|
count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
|
|
local_flush_tlb();
|
|
} else {
|
|
/* flush range by one by one 'invlpg' */
|
|
for (addr = start; addr < end; addr += PAGE_SIZE) {
|
|
count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ONE);
|
|
__flush_tlb_single(addr);
|
|
}
|
|
}
|
|
trace_tlb_flush(TLB_LOCAL_MM_SHOOTDOWN, base_pages_to_flush);
|
|
out:
|
|
if (base_pages_to_flush == TLB_FLUSH_ALL) {
|
|
start = 0UL;
|
|
end = TLB_FLUSH_ALL;
|
|
}
|
|
if (cpumask_any_but(mm_cpumask(mm), smp_processor_id()) < nr_cpu_ids)
|
|
flush_tlb_others(mm_cpumask(mm), mm, start, end);
|
|
preempt_enable();
|
|
}
|
|
|
|
void flush_tlb_page(struct vm_area_struct *vma, unsigned long start)
|
|
{
|
|
struct mm_struct *mm = vma->vm_mm;
|
|
|
|
preempt_disable();
|
|
|
|
if (current->active_mm == mm) {
|
|
if (current->mm)
|
|
__flush_tlb_one(start);
|
|
else
|
|
leave_mm(smp_processor_id());
|
|
}
|
|
|
|
if (cpumask_any_but(mm_cpumask(mm), smp_processor_id()) < nr_cpu_ids)
|
|
flush_tlb_others(mm_cpumask(mm), mm, start, 0UL);
|
|
|
|
preempt_enable();
|
|
}
|
|
|
|
static void do_flush_tlb_all(void *info)
|
|
{
|
|
count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
|
|
__flush_tlb_all();
|
|
if (this_cpu_read(cpu_tlbstate.state) == TLBSTATE_LAZY)
|
|
leave_mm(smp_processor_id());
|
|
}
|
|
|
|
void flush_tlb_all(void)
|
|
{
|
|
count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
|
|
on_each_cpu(do_flush_tlb_all, NULL, 1);
|
|
}
|
|
|
|
static void do_kernel_range_flush(void *info)
|
|
{
|
|
struct flush_tlb_info *f = info;
|
|
unsigned long addr;
|
|
|
|
/* flush range by one by one 'invlpg' */
|
|
for (addr = f->flush_start; addr < f->flush_end; addr += PAGE_SIZE)
|
|
__flush_tlb_single(addr);
|
|
}
|
|
|
|
void flush_tlb_kernel_range(unsigned long start, unsigned long end)
|
|
{
|
|
|
|
/* Balance as user space task's flush, a bit conservative */
|
|
if (end == TLB_FLUSH_ALL ||
|
|
(end - start) > tlb_single_page_flush_ceiling * PAGE_SIZE) {
|
|
on_each_cpu(do_flush_tlb_all, NULL, 1);
|
|
} else {
|
|
struct flush_tlb_info info;
|
|
info.flush_start = start;
|
|
info.flush_end = end;
|
|
on_each_cpu(do_kernel_range_flush, &info, 1);
|
|
}
|
|
}
|
|
|
|
static ssize_t tlbflush_read_file(struct file *file, char __user *user_buf,
|
|
size_t count, loff_t *ppos)
|
|
{
|
|
char buf[32];
|
|
unsigned int len;
|
|
|
|
len = sprintf(buf, "%ld\n", tlb_single_page_flush_ceiling);
|
|
return simple_read_from_buffer(user_buf, count, ppos, buf, len);
|
|
}
|
|
|
|
static ssize_t tlbflush_write_file(struct file *file,
|
|
const char __user *user_buf, size_t count, loff_t *ppos)
|
|
{
|
|
char buf[32];
|
|
ssize_t len;
|
|
int ceiling;
|
|
|
|
len = min(count, sizeof(buf) - 1);
|
|
if (copy_from_user(buf, user_buf, len))
|
|
return -EFAULT;
|
|
|
|
buf[len] = '\0';
|
|
if (kstrtoint(buf, 0, &ceiling))
|
|
return -EINVAL;
|
|
|
|
if (ceiling < 0)
|
|
return -EINVAL;
|
|
|
|
tlb_single_page_flush_ceiling = ceiling;
|
|
return count;
|
|
}
|
|
|
|
static const struct file_operations fops_tlbflush = {
|
|
.read = tlbflush_read_file,
|
|
.write = tlbflush_write_file,
|
|
.llseek = default_llseek,
|
|
};
|
|
|
|
static int __init create_tlb_single_page_flush_ceiling(void)
|
|
{
|
|
debugfs_create_file("tlb_single_page_flush_ceiling", S_IRUSR | S_IWUSR,
|
|
arch_debugfs_dir, NULL, &fops_tlbflush);
|
|
return 0;
|
|
}
|
|
late_initcall(create_tlb_single_page_flush_ceiling);
|