[RFC PATCH 41/57] mm/collapse: give collapse its own trace header
From: Kiryl Shutsemau
Date: Sun Aug 16 2026 - 18:57:48 EST
From: "Kiryl Shutsemau (Meta)" <kas@xxxxxxxxxx>
Every event in include/trace/events/huge_memory.h is a collapse event, and
all but one is emitted from mm/collapse.c. The header is named for
huge_memory.c, which emits none of them, and the tracepoints are built by
khugepaged.c, which emits one.
Rename it to trace/events/collapse.h, with TRACE_SYSTEM to match, and
build the tracepoints in collapse.c.
Two things follow. The pass names a candidate event prints are needed
only where the tracepoints are built, so enum collapse_pass moves out of
mm/collapse.h into collapse.c. And khugepaged.c becomes an ordinary
includer, for the one event it does emit.
The tracefs directory moves with the trace system: events/huge_memory
becomes events/collapse, so anything enabling those events by system name
has to follow.
khugepaged's own selftest does that, and is updated here. So are the two
other in-tree references to the old name: the MAINTAINERS entry for the
header, and the group raw_tp_null_args[] keeps its collapse entries under.
Assisted-by: Claude-Code:claude-opus-5
Signed-off-by: Kiryl Shutsemau (Meta) <kas@xxxxxxxxxx>
---
MAINTAINERS | 2 +-
.../trace/events/{huge_memory.h => collapse.h} | 8 ++++----
kernel/bpf/btf.c | 6 +++---
mm/collapse.c | 17 ++++++++++++++++-
mm/collapse.h | 13 -------------
mm/khugepaged.c | 3 +--
.../selftests/mm/khugepaged_sync_check.c | 10 +++++-----
tools/testing/selftests/mm/vm_util.c | 2 +-
8 files changed, 31 insertions(+), 30 deletions(-)
rename include/trace/events/{huge_memory.h => collapse.h} (98%)
diff --git a/MAINTAINERS b/MAINTAINERS
index 0f513b42bc18..7c179b333e4e 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -17273,7 +17273,7 @@ F: Documentation/ABI/testing/sysfs-kernel-mm-transparent-hugepage
F: Documentation/admin-guide/mm/transhuge.rst
F: include/linux/huge_mm.h
F: include/linux/khugepaged.h
-F: include/trace/events/huge_memory.h
+F: include/trace/events/collapse.h
F: mm/huge_memory.c
F: mm/khugepaged.c
F: mm/mm_slot.h
diff --git a/include/trace/events/huge_memory.h b/include/trace/events/collapse.h
similarity index 98%
rename from include/trace/events/huge_memory.h
rename to include/trace/events/collapse.h
index 6aabf4235648..a3af5d8cc9aa 100644
--- a/include/trace/events/huge_memory.h
+++ b/include/trace/events/collapse.h
@@ -1,9 +1,9 @@
/* SPDX-License-Identifier: GPL-2.0 */
#undef TRACE_SYSTEM
-#define TRACE_SYSTEM huge_memory
+#define TRACE_SYSTEM collapse
-#if !defined(__HUGE_MEMORY_H) || defined(TRACE_HEADER_MULTI_READ)
-#define __HUGE_MEMORY_H
+#if !defined(_TRACE_COLLAPSE_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_COLLAPSE_H
#include <linux/tracepoint.h>
@@ -282,5 +282,5 @@ TRACE_EVENT(mm_khugepaged_scan,
__entry->full_scan_finished)
);
-#endif /* __HUGE_MEMORY_H */
+#endif /* _TRACE_COLLAPSE_H */
#include <trace/define_trace.h>
diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index 22fc8f974be2..505bdbb534e4 100644
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -6683,6 +6683,9 @@ static const struct bpf_raw_tp_null_args raw_tp_null_args[] = {
{ "cachefiles_ondemand_cread", 0x1 },
{ "cachefiles_ondemand_fd_write", 0x1 },
{ "cachefiles_ondemand_fd_release", 0x1 },
+ /* collapse */
+ { "mm_collapse_scan_file", 0x10 },
+ { "mm_collapse_file", 0x10 },
/* ext4, from ext4__mballoc event class */
{ "ext4_mballoc_discard", 0x10 },
{ "ext4_mballoc_free", 0x10 },
@@ -6702,9 +6705,6 @@ static const struct bpf_raw_tp_null_args raw_tp_null_args[] = {
{ "time_out_leases", 0x10 },
/* host1x */
{ "host1x_cdma_push_gather", 0x10000 },
- /* huge_memory */
- { "mm_collapse_scan_file", 0x10 },
- { "mm_collapse_file", 0x10 },
/* kmem */
{ "mm_page_alloc", 0x1 },
{ "mm_page_pcpu_drain", 0x1 },
diff --git a/mm/collapse.c b/mm/collapse.c
index 6c17c83a4e21..952e3f62d920 100644
--- a/mm/collapse.c
+++ b/mm/collapse.c
@@ -26,10 +26,25 @@
#include <linux/vmstat.h>
#include <asm/tlb.h>
-#include <trace/events/huge_memory.h>
#include "collapse.h"
#include "internal.h"
+/*
+ * Which pass of a round reached a verdict on a candidate. Named by the trace
+ * header, which only this file builds, so it need not be shared.
+ */
+enum collapse_pass {
+ COLLAPSE_PASS_ALLOC,
+ COLLAPSE_PASS_REVALIDATE,
+ COLLAPSE_PASS_FAULTIN,
+ COLLAPSE_PASS_FREEZE,
+ COLLAPSE_PASS_COPY,
+ COLLAPSE_PASS_INSTALL,
+};
+
+#define CREATE_TRACE_POINTS
+#include <trace/events/collapse.h>
+
/*
* Anonymous collapse, in rounds.
*
diff --git a/mm/collapse.h b/mm/collapse.h
index 4af7bb9c4261..9e2cec1f250b 100644
--- a/mm/collapse.h
+++ b/mm/collapse.h
@@ -16,19 +16,6 @@
struct collapse_candidate;
struct collapse_retry;
-/*
- * Which pass of a round reached a verdict on a candidate. Only collapse.c
- * produces these; the trace header khugepaged.c builds names them.
- */
-enum collapse_pass {
- COLLAPSE_PASS_ALLOC,
- COLLAPSE_PASS_REVALIDATE,
- COLLAPSE_PASS_FAULTIN,
- COLLAPSE_PASS_FREEZE,
- COLLAPSE_PASS_COPY,
- COLLAPSE_PASS_INSTALL,
-};
-
enum scan_result {
SCAN_FAIL,
SCAN_SUCCEED,
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 967cc472b6dc..f3a7aad5e8f2 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -31,8 +31,7 @@
#include "page_alloc.h"
#include "mm_slot.h"
-#define CREATE_TRACE_POINTS
-#include <trace/events/huge_memory.h>
+#include <trace/events/collapse.h>
static struct task_struct *khugepaged_thread __read_mostly;
static DEFINE_MUTEX(khugepaged_mutex);
diff --git a/tools/testing/selftests/mm/khugepaged_sync_check.c b/tools/testing/selftests/mm/khugepaged_sync_check.c
index 45001996b57a..4c37b697d3dd 100644
--- a/tools/testing/selftests/mm/khugepaged_sync_check.c
+++ b/tools/testing/selftests/mm/khugepaged_sync_check.c
@@ -41,7 +41,7 @@ static unsigned long hpage_pmd_size;
/*
* Each step switches the events off again, but a helper can still give up
* on us in between (a failing sysfs write ends the test from inside
- * thp_write_num()), and huge_memory events left on are the whole machine's
+ * thp_write_num()), and collapse events left on are the whole machine's
* problem, not this test's.
*/
static void trace_events_off(void)
@@ -118,7 +118,7 @@ static void one_step(int iteration)
if (tracing_clear_trace())
ksft_exit_fail_msg("Cannot clear the trace buffer\n");
if (tracing_events_enable(trace_events_fd, true))
- ksft_exit_fail_msg("Cannot enable huge_memory events\n");
+ ksft_exit_fail_msg("Cannot enable collapse events\n");
if (madvise(p, hpage_pmd_size, MADV_HUGEPAGE))
ksft_exit_fail_perror("madvise(MADV_HUGEPAGE)");
@@ -127,7 +127,7 @@ static void one_step(int iteration)
/* Off before anything that can give up: the events are system-wide. */
if (tracing_events_enable(trace_events_fd, false))
- ksft_exit_fail_msg("Cannot disable huge_memory events\n");
+ ksft_exit_fail_msg("Cannot disable collapse events\n");
if (!passed)
ksft_exit_fail_msg("khugepaged did not complete a full pass\n");
@@ -164,9 +164,9 @@ int main(void)
kpageflags_fd = open("/proc/kpageflags", O_RDONLY);
if (kpageflags_fd < 0)
ksft_exit_skip("open(\"/proc/kpageflags\") requires root\n");
- trace_events_fd = tracing_events_open("huge_memory");
+ trace_events_fd = tracing_events_open("collapse");
if (trace_events_fd < 0)
- ksft_exit_skip("huge_memory events require tracefs and root\n");
+ ksft_exit_skip("collapse events require tracefs and root\n");
atexit(trace_events_off);
ksft_set_plan(NR_ITERATIONS);
diff --git a/tools/testing/selftests/mm/vm_util.c b/tools/testing/selftests/mm/vm_util.c
index ee1334778391..32cba59ae49c 100644
--- a/tools/testing/selftests/mm/vm_util.c
+++ b/tools/testing/selftests/mm/vm_util.c
@@ -601,7 +601,7 @@ bool is_range_backed_by_folio_orders(char *start, size_t len, int order,
#define TRACEFS_ROOT "/sys/kernel/tracing"
/*
- * Open the enable file of one ftrace event subsystem (e.g. "huge_memory").
+ * Open the enable file of one ftrace event subsystem (e.g. "collapse").
* Returns a descriptor for tracing_events_enable(), or -1 if tracefs or the
* subsystem is not there. The events are system-wide state: whoever
* switches them on owns them until it switches them off, including on the
--
2.54.0