[PATCH 05/17] x86, mpx: trace when MPX is zapping pages

[Dave Hansen <dave@sr71.net>]

From: Dave Hansen <dave.hansen@linux.intel.com>

When MPX can not free an entire bounds table, it will instead
try to zap unused parts of a bounds table to free the backing
memory.  This decreases RSS (resident set size) without
decreasing the virtual space allocated for bounds tables.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
---

 b/arch/x86/include/asm/trace/mpx.h |   22 ++++++++++++++++++++++
 b/arch/x86/mm/mpx.c                |    1 +
 2 files changed, 23 insertions(+)

diff -puN arch/x86/include/asm/trace/mpx.h~mpx-trace_unmap_zap arch/x86/include/asm/trace/mpx.h
--- a/arch/x86/include/asm/trace/mpx.h~mpx-trace_unmap_zap	2015-03-27 14:35:05.577798421 -0700
+++ b/arch/x86/include/asm/trace/mpx.h	2015-03-27 14:35:05.582798647 -0700
@@ -53,6 +53,28 @@ TRACE_EVENT(bounds_exception_mpx,
 		__entry->bndstatus)
 );
 
+TRACE_EVENT(mpx_unmap_zap,
+
+	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("[0x%p:0x%p]",
+		(void *)__entry->start,
+		(void *)__entry->end
+	)
+);
+
 #else
 
 /*
diff -puN arch/x86/mm/mpx.c~mpx-trace_unmap_zap arch/x86/mm/mpx.c
--- a/arch/x86/mm/mpx.c~mpx-trace_unmap_zap	2015-03-27 14:35:05.579798511 -0700
+++ b/arch/x86/mm/mpx.c	2015-03-27 14:35:05.583798692 -0700
@@ -670,6 +670,7 @@ static int zap_bt_entries(struct mm_stru
 
 		len = min(vma->vm_end, end) - addr;
 		zap_page_range(vma, addr, len, NULL);
+		trace_mpx_unmap_zap(addr, addr+len);
 
 		vma = vma->vm_next;
 		addr = vma->vm_start;
_