[PATCH 07/15] mm: Add ___GFP_NOTRACE

[Tom Zanussi]

Add a gfp flag that allows kmalloc() et al to be used in tracing
functions.

The problem with using kmalloc for tracing is that the tracing
subsystem should be able to trace kmalloc itself, which it can't do
directly because of paths like kmalloc()->trace_kmalloc()->kmalloc()
or kmalloc()->trace_mm_page_alloc()->kmalloc().

With this flag, tracing code could use a special version of kmalloc()
that sets __GFP_NOTRACE on every allocation it does, while leaving the
normal kmalloc() path untouched.

This would allow any tracepoint in the kmalloc path to be avoided via
DEFINE_EVENT_CONDITION() redefinitions of those events, which check
for ___GFP_NOTRACE immediately in their execution and break if set,
thereby avoiding the recursion.

Signed-off-by: Tom Zanussi <tom.zanussi@xxxxxxxxxxxxxxx>
---
 include/linux/gfp.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index b840e3b..acbbc7c 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -34,6 +34,7 @@ struct vm_area_struct;
 #define ___GFP_NO_KSWAPD	0x400000u
 #define ___GFP_OTHER_NODE	0x800000u
 #define ___GFP_WRITE		0x1000000u
+#define ___GFP_NOTRACE		0x2000000u
 /* If the above are modified, __GFP_BITS_SHIFT may need updating */
 
 /*
@@ -97,7 +98,7 @@ struct vm_area_struct;
  */
 #define __GFP_NOTRACK_FALSE_POSITIVE (__GFP_NOTRACK)
 
-#define __GFP_BITS_SHIFT 25	/* Room for N __GFP_FOO bits */
+#define __GFP_BITS_SHIFT 26	/* Room for N __GFP_FOO bits */
 #define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))
 
 /* This equals 0, but use constants in case they ever change */
-- 
1.9.3

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