Re: [PATCH v5 2/6] mm/vmscan: move vmscan tracepoints to a local header

On 11/02/26 at 06:46pm, Ridong Chen wrote:

On 11/2/2026 9:37 AM, Baoquan He wrote:

quoted

On 10/31/26 at 05:00pm, Ridong Chen wrote:

quoted

From: Ridong Chen <redacted>

Move include/trace/events/vmscan.h to mm/trace_vmscan.h so that the
tracepoints can be extended to reference vmscan-internal structures such
as struct scan_control, which is not visible outside mm/.  This mirrors
what several other subsystems already do with their trace headers (e.g.
fs/fuse/fuse_trace.h, fs/gfs2/trace_gfs2.h, fs/lockd/trace.h).  As they
do, set TRACE_INCLUDE_PATH to "." and add mm/ to the include path of
vmscan.o, the only user that defines CREATE_TRACE_POINTS.

No functional change.

Signed-off-by: Ridong Chen <redacted>
Reviewed-by: Barry Song <baohua@kernel.org>
---
  MAINTAINERS                                        | 2 ++
  mm/Makefile                                        | 1 +
  mm/shrinker.c                                      | 2 +-
  include/trace/events/vmscan.h => mm/trace_vmscan.h | 4 ++++
  mm/vmscan.c                                        | 2 +-
  5 files changed, 9 insertions(+), 2 deletions(-)
  rename include/trace/events/vmscan.h => mm/trace_vmscan.h (99%)

diff --git a/MAINTAINERS b/MAINTAINERS
index aaf2825ac945..2ad01107fa05 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS

@@ -17653,6 +17653,7 @@ F:	Documentation/admin-guide/mm/multigen_lru.rst
  F:	Documentation/mm/multigen_lru.rst
  F:	include/linux/mm_inline.h
  F:	include/linux/mmzone.h
+F:	mm/trace_vmscan.h
  F:	mm/vmscan.c
  F:	mm/workingset.c

@@ -17802,6 +17803,7 @@ R:	Shakeel Butt <shakeel.butt@linux.dev>
  R:	Lorenzo Stoakes <ljs@kernel.org>
  L:	linux-mm@kvack.org
  S:	Maintained
+F:	mm/trace_vmscan.h
  F:	mm/vmscan.c
  F:	mm/workingset.c

diff --git a/mm/Makefile b/mm/Makefile
index 2a3ec53d62ee..277b97f7f8d7 100644
--- a/mm/Makefile
+++ b/mm/Makefile

@@ -32,6 +32,7 @@ KCOV_INSTRUMENT_vmstat.o := n
  KCOV_INSTRUMENT_failslab.o := n
  CFLAGS_init-mm.o += -Wno-override-init
+CFLAGS_vmscan.o += -I$(src)

One nit:

Does it really need the above line? It affects mm/shrinker.c too, did your
shrinker.o building fail?

Seems it's redundant because kbuild adds -I$(src) -I$(obj) for every object
in the directory since commit cdd750bfb1f7 ("kbuild: remove 'addtree' and
'flags' magic for header search paths"). Please correct me if I am
wrong.

Hi Baoquan,

Thanks for the review.

The line is needed for vmscan.o, and mm/shrinker.c is fine without it,
because the two files include trace_vmscan.h in different ways.

mm/shrinker.c only does a plain #include "trace_vmscan.h". The lookup
starts from mm/, where the header lives, so no -I is needed.

mm/vmscan.c defines CREATE_TRACE_POINTS before including the header.
In that case <trace/define_trace.h>, included at the end of
trace_vmscan.h, includes the header again to generate the tracepoint
definitions:

#include TRACE_INCLUDE(TRACE_INCLUDE_FILE)  /* -> "./trace_vmscan.h" */

This #include is in include/trace/define_trace.h, so the lookup starts
from include/trace/ and only finds the header through -I. Without the
flag, vmscan.o fails to build:

./include/trace/define_trace.h:118:42: fatal error: ./trace_vmscan.h: No
such file or directory

As for cdd750bfb1f7, it doesn't add -I$(src) for every build. kbuild
only adds -I$(src) -I$(obj) automatically when building with O=
(see "ifdef building_out_of_srctree" in scripts/Makefile.lib). So
with O= the line is indeed redundant and vmscan.o builds fine without
it, but a plain in-tree "make" fails with the error above. The
explicit flag keeps both working.

To be honest, I had the same worry at first: I thought every .c file
that includes the header would need a Makefile change. That's why v3
used a relative TRACE_INCLUDE_PATH (../../mm) instead. Steven corrected
me and pointed out that the proper way is TRACE_INCLUDE_PATH "." plus
-I$(src) for the one object that defines CREATE_TRACE_POINTS [1]. That
turned out to need only this one line. Thanks again to Steven for
that.

You are right, my nit was wrong. Learned it from you, thanks for the
detailed explanation.

[1] https://lore.kernel.org/all/20261014124914.21c21559@gandalf.local.home/ (local)

quoted

Other than the nit, this patch looks good to me,

Reviewed-by: Baoquan He <baoquan.he@linux.dev>

Thanks.

quoted

  mmu-y			:= nommu.o
  mmu-$(CONFIG_MMU)	:= highmem.o memory.o mincore.o \

diff --git a/mm/shrinker.c b/mm/shrinker.c
index 4fb424e721bc..4fbdade6d2f6 100644
--- a/mm/shrinker.c
+++ b/mm/shrinker.c

@@ -3,7 +3,7 @@
  #include <linux/rwsem.h>
  #include <linux/shrinker.h>
  #include <linux/rculist.h>
-#include <trace/events/vmscan.h>
+#include "trace_vmscan.h"
  #include "internal.h"

diff --git a/include/trace/events/vmscan.h b/mm/trace_vmscan.h
similarity index 99%
rename from include/trace/events/vmscan.h
rename to mm/trace_vmscan.h
index 8a872990b4be..ad90f0e9bf2e 100644
--- a/include/trace/events/vmscan.h
+++ b/mm/trace_vmscan.h

@@ -648,4 +648,8 @@ TRACE_EVENT(mm_vmscan_kswapd_clear_hopeless,
  #endif /* _TRACE_VMSCAN_H */
  /* This part must be outside protection */
+#undef TRACE_INCLUDE_FILE
+#undef TRACE_INCLUDE_PATH
+#define TRACE_INCLUDE_PATH .
+#define TRACE_INCLUDE_FILE trace_vmscan
  #include <trace/define_trace.h>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 9959ca158ce8..79d2d614afd0 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c

@@ -71,7 +71,7 @@
  #include "swap.h"
  #define CREATE_TRACE_POINTS
-#include <trace/events/vmscan.h>
+#include "trace_vmscan.h"
  struct scan_control {
  	/* How many pages shrink_list() should reclaim */

-- 
2.43.0

-- 
Best regards
Ridong