mm, rt: kmap_atomic scheduling
In fact, with migrate_disable() existing one could play games with
kmap_atomic. You could save/restore the kmap_atomic slots on context
switch (if there are any in use of course), this should be esp easy now
that we have a kmap_atomic stack.
Something like the below.. it wants replacing all the preempt_disable()
stuff with pagefault_disable() && migrate_disable() of course, but then
you can flip kmaps around like below.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
[dvhart@linux.intel.com: build fix]
Link: http://lkml.kernel.org/r/1311842631.5890.208.camel@twins
[tglx@linutronix.de: Get rid of the per cpu variable and store the idx
and the pte content right away in the task struct.
Shortens the context switch code. ]
diff --git a/arch/x86/kernel/process_32.c b/arch/x86/kernel/process_32.c
index 7305f7d..ee29e6c 100644
--- a/arch/x86/kernel/process_32.c
+++ b/arch/x86/kernel/process_32.c
@@ -36,6 +36,7 @@
#include <linux/uaccess.h>
#include <linux/io.h>
#include <linux/kdebug.h>
+#include <linux/highmem.h>
#include <asm/pgtable.h>
#include <asm/ldt.h>
@@ -214,6 +215,35 @@
}
EXPORT_SYMBOL_GPL(start_thread);
+#ifdef CONFIG_PREEMPT_RT_FULL
+static void switch_kmaps(struct task_struct *prev_p, struct task_struct *next_p)
+{
+ int i;
+
+ /*
+ * Clear @prev's kmap_atomic mappings
+ */
+ for (i = 0; i < prev_p->kmap_idx; i++) {
+ int idx = i + KM_TYPE_NR * smp_processor_id();
+ pte_t *ptep = kmap_pte - idx;
+
+ kpte_clear_flush(ptep, __fix_to_virt(FIX_KMAP_BEGIN + idx));
+ }
+ /*
+ * Restore @next_p's kmap_atomic mappings
+ */
+ for (i = 0; i < next_p->kmap_idx; i++) {
+ int idx = i + KM_TYPE_NR * smp_processor_id();
+
+ if (!pte_none(next_p->kmap_pte[i]))
+ set_pte(kmap_pte - idx, next_p->kmap_pte[i]);
+ }
+}
+#else
+static inline void
+switch_kmaps(struct task_struct *prev_p, struct task_struct *next_p) { }
+#endif
+
/*
* switch_to(x,y) should switch tasks from x to y.
@@ -293,6 +323,8 @@
task_thread_info(next_p)->flags & _TIF_WORK_CTXSW_NEXT))
__switch_to_xtra(prev_p, next_p, tss);
+ switch_kmaps(prev_p, next_p);
+
/*
* Leave lazy mode, flushing any hypercalls made here.
* This must be done before restoring TLS segments so
diff --git a/arch/x86/mm/highmem_32.c b/arch/x86/mm/highmem_32.c
index 252b8f5..0f00d97 100644
--- a/arch/x86/mm/highmem_32.c
+++ b/arch/x86/mm/highmem_32.c
@@ -31,6 +31,7 @@
*/
void *kmap_atomic_prot(struct page *page, pgprot_t prot)
{
+ pte_t pte = mk_pte(page, prot);
unsigned long vaddr;
int idx, type;
@@ -44,7 +45,10 @@
idx = type + KM_TYPE_NR*smp_processor_id();
vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
BUG_ON(!pte_none(*(kmap_pte-idx)));
- set_pte(kmap_pte-idx, mk_pte(page, prot));
+#ifdef CONFIG_PREEMPT_RT_FULL
+ current->kmap_pte[type] = pte;
+#endif
+ set_pte(kmap_pte-idx, pte);
arch_flush_lazy_mmu_mode();
return (void *)vaddr;
@@ -87,6 +91,9 @@
* is a bad idea also, in case the page changes cacheability
* attributes or becomes a protected page in a hypervisor.
*/
+#ifdef CONFIG_PREEMPT_RT_FULL
+ current->kmap_pte[type] = __pte(0);
+#endif
kpte_clear_flush(kmap_pte-idx, vaddr);
kmap_atomic_idx_pop();
arch_flush_lazy_mmu_mode();
diff --git a/arch/x86/mm/iomap_32.c b/arch/x86/mm/iomap_32.c
index 7b179b49..0c953e3 100644
--- a/arch/x86/mm/iomap_32.c
+++ b/arch/x86/mm/iomap_32.c
@@ -56,6 +56,7 @@
void *kmap_atomic_prot_pfn(unsigned long pfn, pgprot_t prot)
{
+ pte_t pte = pfn_pte(pfn, prot);
unsigned long vaddr;
int idx, type;
@@ -64,7 +65,10 @@
type = kmap_atomic_idx_push();
idx = type + KM_TYPE_NR * smp_processor_id();
vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
- set_pte(kmap_pte - idx, pfn_pte(pfn, prot));
+#ifdef CONFIG_PREEMPT_RT_FULL
+ current->kmap_pte[type] = pte;
+#endif
+ set_pte(kmap_pte - idx, pte);
arch_flush_lazy_mmu_mode();
return (void *)vaddr;
@@ -110,6 +114,9 @@
* is a bad idea also, in case the page changes cacheability
* attributes or becomes a protected page in a hypervisor.
*/
+#ifdef CONFIG_PREEMPT_RT_FULL
+ current->kmap_pte[type] = __pte(0);
+#endif
kpte_clear_flush(kmap_pte-idx, vaddr);
kmap_atomic_idx_pop();
}
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 7fb31da..cee935c 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -85,32 +85,51 @@
#if defined(CONFIG_HIGHMEM) || defined(CONFIG_X86_32)
+#ifndef CONFIG_PREEMPT_RT_FULL
DECLARE_PER_CPU(int, __kmap_atomic_idx);
+#endif
static inline int kmap_atomic_idx_push(void)
{
+#ifndef CONFIG_PREEMPT_RT_FULL
int idx = __this_cpu_inc_return(__kmap_atomic_idx) - 1;
-#ifdef CONFIG_DEBUG_HIGHMEM
+# ifdef CONFIG_DEBUG_HIGHMEM
WARN_ON_ONCE(in_irq() && !irqs_disabled());
BUG_ON(idx > KM_TYPE_NR);
-#endif
+# endif
return idx;
+#else
+ current->kmap_idx++;
+ BUG_ON(current->kmap_idx > KM_TYPE_NR);
+ return current->kmap_idx - 1;
+#endif
}
static inline int kmap_atomic_idx(void)
{
+#ifndef CONFIG_PREEMPT_RT_FULL
return __this_cpu_read(__kmap_atomic_idx) - 1;
+#else
+ return current->kmap_idx - 1;
+#endif
}
static inline void kmap_atomic_idx_pop(void)
{
-#ifdef CONFIG_DEBUG_HIGHMEM
+#ifndef CONFIG_PREEMPT_RT_FULL
+# ifdef CONFIG_DEBUG_HIGHMEM
int idx = __this_cpu_dec_return(__kmap_atomic_idx);
BUG_ON(idx < 0);
-#else
+# else
__this_cpu_dec(__kmap_atomic_idx);
+# endif
+#else
+ current->kmap_idx--;
+# ifdef CONFIG_DEBUG_HIGHMEM
+ BUG_ON(current->kmap_idx < 0);
+# endif
#endif
}
diff --git a/include/linux/sched.h b/include/linux/sched.h
index 96c3caa..e5f6eac 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -23,6 +23,7 @@
#include <linux/nodemask.h>
#include <linux/mm_types.h>
+#include <asm/kmap_types.h>
#include <asm/page.h>
#include <asm/ptrace.h>
#include <asm/cputime.h>
@@ -1449,6 +1450,12 @@
struct rcu_head put_rcu;
int softirq_nestcnt;
#endif
+#ifdef CONFIG_PREEMPT_RT_FULL
+# if defined CONFIG_HIGHMEM || defined CONFIG_X86_32
+ int kmap_idx;
+ pte_t kmap_pte[KM_TYPE_NR];
+# endif
+#endif
};
#ifdef CONFIG_NUMA_BALANCING
diff --git a/mm/highmem.c b/mm/highmem.c
index b32b70c..b1c7d43 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -29,10 +29,11 @@
#include <linux/kgdb.h>
#include <asm/tlbflush.h>
-
+#ifndef CONFIG_PREEMPT_RT_FULL
#if defined(CONFIG_HIGHMEM) || defined(CONFIG_X86_32)
DEFINE_PER_CPU(int, __kmap_atomic_idx);
#endif
+#endif
/*
* Virtual_count is not a pure "count".
@@ -47,8 +48,9 @@
unsigned long totalhigh_pages __read_mostly;
EXPORT_SYMBOL(totalhigh_pages);
-
+#ifndef CONFIG_PREEMPT_RT_FULL
EXPORT_PER_CPU_SYMBOL(__kmap_atomic_idx);
+#endif
unsigned int nr_free_highpages (void)
{
diff --git a/mm/memory.c b/mm/memory.c
index f4e6b70..9065918 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3760,6 +3760,7 @@
#ifdef CONFIG_PREEMPT_RT_FULL
void pagefault_disable(void)
{
+ migrate_disable();
current->pagefault_disabled++;
/*
* make sure to have issued the store before a pagefault
@@ -3777,6 +3778,7 @@
*/
barrier();
current->pagefault_disabled--;
+ migrate_enable();
}
EXPORT_SYMBOL(pagefault_enable);
#endif