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Date: Thu, 23 Jul 2009 17:04:21 +0800
From: Li Zefan <lizf@...fujitsu.com>
To: Roland Dreier <rdreier@...co.com>
CC: Andrew Morton <akpm@...ux-foundation.org>,
linux-kernel@...r.kernel.org, Jeff Squyres <jsquyres@...co.com>
Subject: Re: [PATCH/RFC] ummunot: Userspace support for MMU notifications
> > > 1. ioctl() to register/unregister an address range to watch in the
> > > kernel (cf struct ummunot_register_ioctl in <linux/ummunot.h>).
> > >
> > > 2. read() to retrieve events generated when a mapping in a watched
> > > address range is invalidated (cf struct ummunot_event in
> > > <linux/ummunot.h>). select()/poll()/epoll() and SIGIO are handled
> > > for this IO.
> > >
> > > 3. mmap() one page at offset 0 to map a kernel page that contains a
> > > generation counter that is incremented each time an event is
> > > generated. This allows userspace to have a fast path that checks
> > > that no events have occurred without a system call.
> >
> > If you stand back and squint, each of 1, 2 and 3 are things which the
> > kernel already provides for the delivery of ftrace events to userspace.
> >
> > Did you look at reusing all that stuff?
>
> No, not really... will investigate a bit further. Any pointers to how
> the ftrace stuff might work?
This can be implemented as a tracer or trace events, though I'm
not sure if it can fully meet your requirements or not.
To implement it as trace events, we add tracepoints in mmu_inlivadate_xxx(),
and define some TRACE_EVENT() macros.
And below shows how to use it:
# mount -t debugfs xxx /mnt
# cd /mnt/tracing/
# echo 1 > events/mmu/enable
# echo '(start >= 10000000 && end <= 10004096) || \
(start >= 20000000 && end <= 20004096)' > events/mmu/filter
# cat trace_pipe
bash-2066 [001] 795.239077: mmu_invalidate_range_start: start=10000000 end=10000100
bash-2066 [001] 795.239091: mmu_invalidate_range_start: start=10000000 end=10000100
bash-2066 [001] 795.239098: mmu_invalidate_range_start: start=10000000 end=10000100
cat-2189 [001] 795.239502: mmu_invalidate_page: start=20000000 end=20003000
cat-2189 [001] 795.239578: mmu_invalidate_page: start=20000000 end=20003000
bash-2066 [001] 795.239626: mmu_invalidate_page: start=20000000 end=20003000
The patch is extremely simple:
---
include/linux/mmu_notifier.h | 4 +++
include/trace/events/mmu.h | 55 ++++++++++++++++++++++++++++++++++++++++++
mm/mmu_notifier.c | 3 ++
3 files changed, 62 insertions(+), 0 deletions(-)
create mode 100644 include/trace/events/mmu.h
diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h
index b77486d..49ff4cc 100644
--- a/include/linux/mmu_notifier.h
+++ b/include/linux/mmu_notifier.h
@@ -5,6 +5,8 @@
#include <linux/spinlock.h>
#include <linux/mm_types.h>
+#include <trace/events/mmu.h>
+
struct mmu_notifier;
struct mmu_notifier_ops;
@@ -178,6 +180,7 @@ static inline int mmu_notifier_clear_flush_young(struct mm_struct *mm,
static inline void mmu_notifier_invalidate_page(struct mm_struct *mm,
unsigned long address)
{
+ trace_mmu_invalidate_page(address);
if (mm_has_notifiers(mm))
__mmu_notifier_invalidate_page(mm, address);
}
@@ -185,6 +188,7 @@ static inline void mmu_notifier_invalidate_page(struct mm_struct *mm,
static inline void mmu_notifier_invalidate_range_start(struct mm_struct *mm,
unsigned long start, unsigned long end)
{
+ trace_mmu_invalidate_range_start(start, end);
if (mm_has_notifiers(mm))
__mmu_notifier_invalidate_range_start(mm, start, end);
}
diff --git a/include/trace/events/mmu.h b/include/trace/events/mmu.h
new file mode 100644
index 0000000..0d6bbcd
--- /dev/null
+++ b/include/trace/events/mmu.h
@@ -0,0 +1,55 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM mmu
+
+#if !defined(_TRACE_MMU_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_MMU_H
+
+#include <linux/tracepoint.h>
+
+#ifdef CONFIG_MMU_NOTIFIER
+
+TRACE_EVENT(mmu_invalidate_page,
+
+ TP_PROTO(unsigned long addr),
+
+ TP_ARGS(addr),
+
+ TP_STRUCT__entry(
+ __field( unsigned long, start )
+ __field( unsigned long, end )
+ ),
+
+ TP_fast_assign(
+ __entry->start = addr;
+ __entry->end = addr + PAGE_SIZE;
+ ),
+
+ TP_printk("start=%lu end=%lu", __entry->start, __entry->end)
+);
+
+TRACE_EVENT(mmu_invalidate_range_start,
+
+ TP_PROTO(unsigned long start, unsigned long end),
+
+ TP_ARGS(start, end),
+
+ TP_STRUCT__entry(
+ __field( unsigned long, start )
+ __field( unsigned long, end )
+ ),
+
+ TP_fast_assign(
+ __entry->start = start;
+ __entry->end = end;
+ ),
+
+ TP_printk("start=%lu end=%lu", __entry->start, __entry->end)
+);
+
+#endif /* CONFIG_MMU_NOTIFIER */
+
+#endif /* _TRACE_MMU_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
+
diff --git a/mm/mmu_notifier.c b/mm/mmu_notifier.c
index 5f4ef02..685ffdc 100644
--- a/mm/mmu_notifier.c
+++ b/mm/mmu_notifier.c
@@ -17,6 +17,9 @@
#include <linux/rcupdate.h>
#include <linux/sched.h>
+#define CREATE_TRACE_POINTS
+#include <trace/events/mmu.h>
+
/*
* This function can't run concurrently against mmu_notifier_register
* because mm->mm_users > 0 during mmu_notifier_register and exit_mmap
--
1.6.3
--
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