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Date: Fri, 09 Oct 2009 15:05:30 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
"hugh.dickins" <hugh.dickins@...cali.co.uk>,
Ingo Molnar <mingo@...e.hu>,
David Howells <dhowells@...hat.com>,
lkml <linux-kernel@...r.kernel.org>,
linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [RFC][PATCH 0/4] stack based kmap_atomic -v2
On Fri, 2009-10-09 at 01:22 +0200, Peter Zijlstra wrote:
>
> Maybe FRV can do a kind of kmap-stack switch on (soft)irq enter/exit
> in order to stay below 5 entries.
David, would something like the below work for you?
You'd need to disallow nested hardirqs, but I'm not sure FRV suffers
that particular issue?
---
Index: linux-2.6/include/linux/highmem.h
===================================================================
--- linux-2.6.orig/include/linux/highmem.h
+++ linux-2.6/include/linux/highmem.h
@@ -83,6 +83,30 @@ static inline void *kmap_atomic(struct p
#endif /* CONFIG_HIGHMEM */
+enum kmap_context {
+ KMAP_USER = 0,
+ KMAP_SOFTIRQ,
+ KMAP_IRQ,
+ KMAP_NMI,
+ KMAP_CONTEXT_NR,
+}
+
+#if !defined(CONFIG_HIGHMEM) || !defined(ARCH_HAS_KMAP_SWITCH)
+/*
+ * Routines the arch can use to save/restore kmap_atomic stacks.
+ *
+ * This can be useful when an arch has limited kmap_atomic slots
+ * and wants to deal with context nesting.
+ */
+static inline void kmap_atomic_save(enum kmap_context kctx)
+{
+}
+
+static inline void kmap_atomic_restore(enum kmap_context kctx)
+{
+}
+#endif
+
/* when CONFIG_HIGHMEM is not set these will be plain clear/copy_page */
#ifndef clear_user_highpage
static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
Index: linux-2.6/kernel/softirq.c
===================================================================
--- linux-2.6.orig/kernel/softirq.c
+++ linux-2.6/kernel/softirq.c
@@ -283,6 +283,8 @@ void irq_enter(void)
tick_check_idle(cpu);
} else
__irq_enter();
+
+ kmap_atomic_save(KMAP_IRQ);
}
#ifdef __ARCH_IRQ_EXIT_IRQS_DISABLED
@@ -296,11 +298,15 @@ void irq_enter(void)
*/
void irq_exit(void)
{
+ kmap_atomic_restore(KMAP_IRQ);
account_system_vtime(current);
trace_hardirq_exit();
sub_preempt_count(IRQ_EXIT_OFFSET);
- if (!in_interrupt() && local_softirq_pending())
+ if (!in_interrupt() && local_softirq_pending()) {
+ kmap_atomic_save(KMAP_SOFTIRQ);
invoke_softirq();
+ kmap_atomic_restore(KMAP_SOFTIRQ);
+ }
#ifdef CONFIG_NO_HZ
/* Make sure that timer wheel updates are propagated */
Index: linux-2.6/arch/frv/include/asm/highmem.h
===================================================================
--- linux-2.6.orig/arch/frv/include/asm/highmem.h
+++ linux-2.6/arch/frv/include/asm/highmem.h
@@ -121,20 +121,13 @@ static inline void *kmap_atomic(struct p
type = kmap_atomic_idx_push();
paddr = page_to_phys(page);
- switch (type) {
- case 0: return __kmap_atomic_primary(0, paddr, 2);
- case 1: return __kmap_atomic_primary(1, paddr, 3);
- case 2: return __kmap_atomic_primary(2, paddr, 4);
- case 3: return __kmap_atomic_primary(3, paddr, 5);
+ switch (type + 4) {
case 4: return __kmap_atomic_primary(4, paddr, 6);
case 5: return __kmap_atomic_primary(5, paddr, 7);
case 6: return __kmap_atomic_primary(6, paddr, 8);
case 7: return __kmap_atomic_primary(7, paddr, 9);
case 8: return __kmap_atomic_primary(8, paddr, 10);
- case 9 ... 9 + NR_TLB_LINES - 1:
- return __kmap_atomic_secondary(type - 9, paddr);
-
default:
BUG();
return NULL;
@@ -156,27 +149,53 @@ do { \
static inline void kunmap_atomic(void *kvaddr)
{
int type = kmap_atomic_idx_pop();
- switch (type) {
- case 0: __kunmap_atomic_primary(0, 2); break;
- case 1: __kunmap_atomic_primary(1, 3); break;
- case 2: __kunmap_atomic_primary(2, 4); break;
- case 3: __kunmap_atomic_primary(3, 5); break;
+ switch (type+4) {
case 4: __kunmap_atomic_primary(4, 6); break;
case 5: __kunmap_atomic_primary(5, 7); break;
case 6: __kunmap_atomic_primary(6, 8); break;
case 7: __kunmap_atomic_primary(7, 9); break;
case 8: __kunmap_atomic_primary(8, 10); break;
- case 9 ... 9 + NR_TLB_LINES - 1:
- __kunmap_atomic_secondary(type - 9, kvaddr);
- break;
-
default:
BUG();
}
pagefault_enable();
}
+#define ARCH_HAS_KMAP_SWITCH
+
+struct kmap_atomic_context {
+ pte_t maps[KM_TYPE_NR];
+ int nr;
+};
+
+DECLARE_PER_CPU(struct kmap_atomic_context, kmap_ctxs[KMAP_CONTEXT_NR]);
+
+static inline void kmap_atomic_save(enum kmap_context kctx)
+{
+ struct kmap_atomic_context *kac = &__get_cpu_var(kmap_ctxs)[kctx];
+ int *idx = &__get_cpu_var(__kmap_atomic_idx);
+
+ kac->nr = *idx;
+
+ if (*idx) {
+ /* XXX save maps */ ;
+ *idx = 0;
+ }
+}
+
+static inline void kmap_atomic_restore(enum kmap_context kctx)
+{
+ struct kmap_atomic_context *kac = &__get_cpu_var(kmap_ctxs)[kctx];
+ int *idx = &__get_cpu_var(__kmap_atomic_idx);
+
+ *idx = kac->nr;
+ if (*idx) {
+ /* XXX restore maps */ ;
+ }
+}
+
+
#endif /* !__ASSEMBLY__ */
#endif /* __KERNEL__ */
Index: linux-2.6/arch/frv/include/asm/kmap_types.h
===================================================================
--- linux-2.6.orig/arch/frv/include/asm/kmap_types.h
+++ linux-2.6/arch/frv/include/asm/kmap_types.h
@@ -3,27 +3,8 @@
#define _ASM_KMAP_TYPES_H
enum km_type {
- /* arch specific kmaps - change the numbers attached to these at your peril */
- __KM_CACHE, /* cache flush page attachment point */
- __KM_PGD, /* current page directory */
- __KM_ITLB_PTD, /* current instruction TLB miss page table lookup */
- __KM_DTLB_PTD, /* current data TLB miss page table lookup */
-
/* general kmaps */
- KM_BOUNCE_READ,
- KM_SKB_SUNRPC_DATA,
- KM_SKB_DATA_SOFTIRQ,
- KM_USER0,
- KM_USER1,
- KM_BIO_SRC_IRQ,
- KM_BIO_DST_IRQ,
- KM_PTE0,
- KM_PTE1,
- KM_IRQ0,
- KM_IRQ1,
- KM_SOFTIRQ0,
- KM_SOFTIRQ1,
- KM_TYPE_NR
+ KM_TYPE_NR = 5
};
#endif
--
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