linux-kernel - [RFC][PATCH] trace transparent huge page splits

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Date:	Mon, 31 Jan 2011 16:55:47 -0800
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	linux-mm@...ck.org, Michael J Wolf <mjwolf@...ibm.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Dave Hansen <dave@...ux.vnet.ibm.com>
Subject: [RFC][PATCH] trace transparent huge page splits


When we see transparent huge pages being broken down, we generally
have no idea of finding anything out about how it happened, or what
it affected.

A simple static tracepoint like this should at least get us some
minimal information like a stack trace, the virtual address, and
the mm that it happened to.

I'm not sure if there is a better way to do this with any of the
other tracing mechanisms, but this seems to work at least for me.
Does anybody else have a better way?  Is it worth merging this
kind of stuff, or is it best left out of tree as a debugging
patch?

Signed-off-by: Dave Hansen <dave@...ux.vnet.ibm.com>
---

 linux-2.6.git-dave/include/trace/events/huge_memory.h |   32 ++++++++++++++++++
 linux-2.6.git-dave/mm/huge_memory.c                   |    5 ++
 2 files changed, 37 insertions(+)

diff -puN /dev/null include/trace/events/huge_memory.h
--- /dev/null	2011-01-21 14:16:26.635488000 -0800
+++ linux-2.6.git-dave/include/trace/events/huge_memory.h	2011-01-31 16:42:37.607926454 -0800
@@ -0,0 +1,32 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM huge_memory
+
+#if !defined(_TRACE_HUGE_MEMORY_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_HUGE_MEMORY_H
+
+#include <linux/types.h>
+#include <linux/tracepoint.h>
+
+TRACE_EVENT(mm_huge_memory_split,
+
+	TP_PROTO(struct mm_struct *mm, unsigned long address),
+
+	TP_ARGS(mm, address),
+
+	TP_STRUCT__entry(
+		__field(struct mm_struct *, mm)
+		__field(unsigned long,	    address)
+	),
+
+	TP_fast_assign(
+		__entry->mm	 = mm;
+		__entry->address = address;
+	),
+
+	TP_printk("mm=%p address=%p", __entry->mm, (void *)__entry->address)
+);
+
+#endif /* _TRACE_HUGE_MEMORY_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff -puN include/linux/huge_mm.h~huge_mem_trace include/linux/huge_mm.h
diff -puN mm/huge_memory.c~huge_mem_trace mm/huge_memory.c
--- linux-2.6.git/mm/huge_memory.c~huge_mem_trace	2011-01-31 16:40:38.752014520 -0800
+++ linux-2.6.git-dave/mm/huge_memory.c	2011-01-31 16:41:15.671987202 -0800
@@ -21,6 +21,9 @@
 #include <asm/pgalloc.h>
 #include "internal.h"
 
+#define CREATE_TRACE_POINTS
+#include <trace/events/huge_memory.h>
+
 /*
  * By default transparent hugepage support is enabled for all mappings
  * and khugepaged scans all mappings. Defrag is only invoked by
@@ -1254,6 +1257,8 @@ static int __split_huge_page_map(struct 
 	pgtable_t pgtable;
 	unsigned long haddr;
 
+	trace_mm_huge_memory_split(vma->vm_mm, address);
+
 	spin_lock(&mm->page_table_lock);
 	pmd = page_check_address_pmd(page, mm, address,
 				     PAGE_CHECK_ADDRESS_PMD_SPLITTING_FLAG);
diff -puN mm/vmscan.c~huge_mem_trace mm/vmscan.c
diff -puN mm/page_io.c~huge_mem_trace mm/page_io.c
diff -puN block/blk-core.c~huge_mem_trace block/blk-core.c
_
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