* [PATCH v2 1/4] alloc_tag: Add trace events for tracing allocations
2026-10-07 22:39 [PATCH v2 0/4] alloc_tag: Introduce selective tracing for MAP Abhishek Bapat
@ 2026-10-07 22:39 ` Abhishek Bapat
2026-10-07 22:40 ` [PATCH v2 2/4] alloc_tag: Introduce IOCTLs to toggle allocation tracepoints Abhishek Bapat
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: Abhishek Bapat @ 2026-10-07 22:39 UTC (permalink / raw)
To: Suren Baghdasaryan, Hao Ge, Andrew Morton
Cc: linux-kernel, linux-mm, linux-trace-kernel, Abhishek Bapat
The memory allocation profiling framework intercepts allocations across
the core subsystems, but currently lacks runtime tracing hooks for
standard observability tools to dynamically track the context (stack
traces and lifecycles of the individual memory chunks) of the
allocations made.
Introduce three standard trace events to allow this tracking:
1. `alloc_tag_hit`: Fired at the exact call site. This allows userspace
tools to trigger and capture a call stack.
2. `alloc_tag_mem_alloced`: Fired in alloc_tag_add upon successful
allocation. It records the allocated size, the tag, and the uniquely
generated `ptr` value which is `codetag_ref` for slab and percpu
allocators and the pointer to the head `struct page` for the page
allocator.
3. `alloc_tag_mem_freed`: Fired in alloc_tag_sub right before memory is
freed, yielding the same `ptr` value to allow tracing tools to find
the corresponding allocation.
Because the introduced trace events occur at different stages in the
call stack, userspace tracing tools must stitch them together to form a
complete picture of a buffer's lifetime. Here's an example of how
userspace correlates these three events:
1. On `alloc_tag_hit`: The tool captures the stack trace and caches it,
keyed by the combination of the current thread's PID and the `tag`.
2. On `alloc_tag_mem_alloced`: The tool extracts the PID and `tag` from
the event and looks up the stack trace cached in step 1. It creates a
new active allocation record, mapping the new provided `ptr` value
to this cached stack trace and the newly returned allocation size.
3. On `alloc_tag_mem_freed`: When the memory is freed, the event yields
the same `ptr` value. The tool uses this reference to look up the
original allocation record, correlates the free, and safely retires
the tracking entry.
Modify `alloc_tag_add()` and `alloc_tag_sub()` with a `ptr` argument to
map frees to allocations in the trace events. Slab and percpu pass the
address of the object's `codetag_ref`. The page allocator passes the
head `struct page` because its `codetag_ref` is a temporary copy on the
stack.
Also, introduce `alloc_tag_trace_key` static key to minimize the
overhead when no tags are being traced (the usual case). Once tracing
for any tag is requested, the key is set, opening the path to check
whether tracing is enabled for the current tag.
Note that the mechanism to enable tag tracing is implemented in the next
patch, therefore for now, `alloc_tag_trace_key` stays always unset.
Signed-off-by: Abhishek Bapat <abhishekbapat@google.com>
---
Documentation/mm/allocation-profiling.rst | 53 ++++++++++
MAINTAINERS | 1 +
include/linux/alloc_tag.h | 67 +++++++++---
include/trace/events/alloc_tag.h | 122 ++++++++++++++++++++++
mm/alloc_tag.c | 28 +++++
mm/page_alloc.c | 4 +-
mm/percpu.c | 12 ++-
mm/slub.c | 6 +-
8 files changed, 269 insertions(+), 24 deletions(-)
create mode 100644 include/trace/events/alloc_tag.h
diff --git a/Documentation/mm/allocation-profiling.rst b/Documentation/mm/allocation-profiling.rst
index b11ea77c0673..b241450394df 100644
--- a/Documentation/mm/allocation-profiling.rst
+++ b/Documentation/mm/allocation-profiling.rst
@@ -129,6 +129,59 @@ To do so:
- Then, use the following form for your allocations:
alloc_hooks_tag(ht->your_saved_tag, kmalloc_noprof(...))
+Tracing
+=======
+
+Three trace events are available under `/sys/kernel/tracing/events/alloc_tag` to
+expose the full call stack and the lifetime of individual allocations:
+
+- `alloc_tag_hit`: Fired at the exact call site, before the allocation happens.
+ Can be used to capture the call stack of the caller.
+
+- `alloc_tag_mem_alloced`: Fired once the allocation succeeds. Carries the `ptr`,
+ `tag` and `bytes` for each allocation.
+
+- `alloc_tag_mem_freed`: Fired before memory is freed. Carries the same
+ `ptr`, `tag` and `bytes` as the matching alloc event.
+
+`ptr` identifies the allocation, and its meaning depends on the allocator:
+
+- slab and percpu: the address of the object's `codetag_ref`
+- page allocator: the `struct page` pointer of the head page
+
+Correlating the events
+----------------------
+
+`alloc_tag_hit` and `alloc_tag_mem_alloced` come from different points in the
+call stack, so they have to be stitched together by the user consuming the
+events. Here's a typical flow:
+
+1. On `alloc_tag_hit`: Capture the stack trace and cache it keyed by `(pid, tag)`.
+
+2. On `alloc_tag_mem_alloced`: Look up the cached stack trace by `(pid, tag)`,
+ then create an active allocation record keyed by `ptr` that holds the stack
+ trace and `bytes`.
+
+3. On `alloc_tag_mem_freed`: Look up the record by `ptr` and retire it.
+
+Limitations
+-----------
+
+- For the page allocator, events are generated for the original allocation and
+ the free only. If the tag reference is split or moved to another folio in
+ between, no event is generated for that. As a result:
+
+ - a free event may carry a `ptr` that never appeared in an alloc event;
+ - `bytes` in a free event may be smaller than in the matching alloc event.
+
+ Tools should correlate on `ptr` but must not assume that freed bytes equal
+ allocated bytes, or that every free has a matching alloc.
+
+- Freeing a non-compound high-order page with `__free_pages()` while another CPU
+ holds a reference frees the tail pages immediately and the head page later when
+ the reference is dropped. The free event is emitted at the second point and
+ reports `PAGE_SIZE` rather than the full size.
+
Notes
=====
diff --git a/MAINTAINERS b/MAINTAINERS
index 5c38da7090db..751ce786a378 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -17100,6 +17100,7 @@ S: Maintained
F: Documentation/mm/allocation-profiling.rst
F: include/linux/alloc_tag.h
F: include/linux/pgalloc_tag.h
+F: include/trace/events/alloc_tag.h
F: include/uapi/linux/alloc_tag.h
F: mm/alloc_tag.c
F: tools/testing/selftests/alloc_tag/
diff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h
index 7f2d80a59792..49825177d8c8 100644
--- a/include/linux/alloc_tag.h
+++ b/include/linux/alloc_tag.h
@@ -128,12 +128,33 @@ DECLARE_PER_CPU(struct alloc_tag_counters, _shared_alloc_tag);
DECLARE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
mem_alloc_profiling_key);
+DECLARE_STATIC_KEY_FALSE(alloc_tag_trace_key);
+
static inline bool mem_alloc_profiling_enabled(void)
{
return static_branch_maybe(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
&mem_alloc_profiling_key);
}
+static inline bool alloc_tag_trace_enabled(void)
+{
+ return static_branch_unlikely(&alloc_tag_trace_key);
+}
+
+void alloc_tag_trace_mem_alloc(const void *ptr, struct alloc_tag *tag,
+ size_t bytes);
+
+void alloc_tag_trace_mem_free(const void *ptr, struct alloc_tag *tag,
+ size_t bytes);
+
+void __alloc_tag_trace_hit(struct alloc_tag *tag);
+
+static __always_inline void alloc_tag_trace_hit(struct alloc_tag *tag)
+{
+ if (alloc_tag_trace_enabled())
+ __alloc_tag_trace_hit(tag);
+}
+
bool mem_alloc_profiling_permanently_disabled(void);
static inline struct alloc_tag_counters alloc_tag_read(struct alloc_tag *tag)
@@ -198,13 +219,19 @@ static inline bool alloc_tag_ref_set(union codetag_ref *ref, struct alloc_tag *t
return true;
}
-static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag, size_t bytes)
+static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag, size_t bytes,
+ const void *ptr)
{
- if (likely(alloc_tag_ref_set(ref, tag)))
+ if (likely(alloc_tag_ref_set(ref, tag))) {
this_cpu_add(tag->counters->bytes, bytes);
+
+ if (alloc_tag_trace_enabled())
+ /* Trace successful allocs with their unique ptr */
+ alloc_tag_trace_mem_alloc(ptr, tag, bytes);
+ }
}
-static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes)
+static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes, const void *ptr)
{
struct alloc_tag *tag;
@@ -222,6 +249,10 @@ static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes)
this_cpu_sub(tag->counters->bytes, bytes);
this_cpu_dec(tag->counters->calls);
+ if (alloc_tag_trace_enabled())
+ /* Trace frees with their unique ptr */
+ alloc_tag_trace_mem_free(ptr, tag, bytes);
+
ref->ct = NULL;
}
@@ -243,25 +274,29 @@ static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag)
static inline bool mem_alloc_profiling_enabled(void) { return false; }
static inline bool mem_alloc_profiling_permanently_disabled(void) { return true; }
static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag,
- size_t bytes) {}
-static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes) {}
+ size_t bytes, const void *ptr) {}
+static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes,
+ const void *ptr) {}
static inline void alloc_tag_set_inaccurate(struct alloc_tag *tag) {}
static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag) { return false; }
+#define alloc_tag_trace_hit(_tag) /* NOOP */
#define alloc_tag_record(p) do {} while (0)
#endif /* CONFIG_MEM_ALLOC_PROFILING */
-#define alloc_hooks_tag(_tag, _do_alloc) \
-({ \
- typeof(_do_alloc) _res; \
- if (mem_alloc_profiling_enabled()) { \
- struct alloc_tag * __maybe_unused _old; \
- _old = alloc_tag_save(_tag); \
- _res = _do_alloc; \
- alloc_tag_restore(_tag, _old); \
- } else \
- _res = _do_alloc; \
- _res; \
+#define alloc_hooks_tag(_tag, _do_alloc) \
+({ \
+ typeof(_do_alloc) _res; \
+ if (mem_alloc_profiling_enabled()) { \
+ struct alloc_tag * __maybe_unused _old; \
+ /* Fired here to cleanly capture the caller's stack trace */ \
+ alloc_tag_trace_hit(_tag); \
+ _old = alloc_tag_save(_tag); \
+ _res = _do_alloc; \
+ alloc_tag_restore(_tag, _old); \
+ } else \
+ _res = _do_alloc; \
+ _res; \
})
#define alloc_hooks(_do_alloc) \
diff --git a/include/trace/events/alloc_tag.h b/include/trace/events/alloc_tag.h
new file mode 100644
index 000000000000..b79efb7dd25c
--- /dev/null
+++ b/include/trace/events/alloc_tag.h
@@ -0,0 +1,122 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM alloc_tag
+
+#if !defined(_TRACE_ALLOC_TAG_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_ALLOC_TAG_H
+
+#include <linux/tracepoint.h>
+
+/*
+ * alloc_tag_hit is generated at the exact allocation call site and can be
+ * used to capture a clean stack trace.
+ *
+ * To link this stack trace to the actual allocated memory chunk, tools must
+ * correlate this event with the resulting alloc_tag_mem_alloced event. Since
+ * multiple threads can hit the same tag simultaneously, tools must match BOTH
+ * the `tag` field and the implicitly recorded PID provided by the core
+ * tracing subsystem.
+ */
+TRACE_EVENT(alloc_tag_hit,
+ TP_PROTO(struct alloc_tag *tag),
+
+ TP_ARGS(tag),
+
+ TP_STRUCT__entry(__field(struct alloc_tag *, tag)
+ __string(modname, tag->ct.modname ? tag->ct.modname : "NONE")
+ __string(filename, tag->ct.filename)
+ __string(function, tag->ct.function)
+ __field(unsigned int, lineno)
+ ),
+
+ TP_fast_assign(__entry->tag = tag;
+ __assign_str(modname);
+ __assign_str(filename);
+ __assign_str(function);
+ __entry->lineno = tag->ct.lineno;
+ ),
+
+ TP_printk("tag %p, module: %s, filename: %s, function %s, lineno %u",
+ __entry->tag,
+ __get_str(modname),
+ __get_str(filename),
+ __get_str(function),
+ __entry->lineno
+ )
+);
+
+/*
+ * alloc_tag_mem_alloced is generated after memory is successfully allocated.
+ * It captures the exact byte size.
+ *
+ * The `ptr` value identifies the memory chunk for tracking its lifecycle
+ * (e.g., matching it with alloc_tag_mem_freed).
+ * - slab and percpu allocators: address of the object's codetag_ref
+ * - page allocator: the head struct page of the allocation
+ *
+ * Because the kernel isolates active allocations within the task struct
+ * (current->alloc_tag), this event will always share the same implicit PID as
+ * its corresponding alloc_tag_hit event. Tools should use the combination
+ * PID + `tag` to correlate them.
+ */
+TRACE_EVENT(alloc_tag_mem_alloced,
+ TP_PROTO(const void *ptr, struct alloc_tag *tag, size_t bytes),
+
+ TP_ARGS(ptr, tag, bytes),
+
+ TP_STRUCT__entry(__field(const void *, ptr)
+ __field(struct alloc_tag *, tag)
+ __field(size_t, bytes)
+ ),
+
+ TP_fast_assign(__entry->ptr = ptr;
+ __entry->tag = tag;
+ __entry->bytes = bytes;
+ ),
+
+ TP_printk("ptr %p, tag %p, bytes %zu",
+ __entry->ptr,
+ __entry->tag,
+ __entry->bytes
+ )
+);
+
+/*
+ * alloc_tag_mem_freed event is generated immediately before memory is
+ * freed. The `ptr` value matches the one emitted during allocation,
+ * allowing tools to match it to its corresponding allocation and
+ * call stack.
+ *
+ * Page allocator caveat: Pages can be split or moved to another folio
+ * after the alloc event with no new events generated for that. As a
+ * result, a free event may carry a `ptr` that never appeared in an
+ * alloc event, and the `bytes` may be smaller than in the matching
+ * alloc event. Tools must not assume alloc bytes == free bytes, nor
+ * that every free has a matching alloc.
+ */
+TRACE_EVENT(alloc_tag_mem_freed,
+ TP_PROTO(const void *ptr, struct alloc_tag *tag, size_t bytes),
+
+ TP_ARGS(ptr, tag, bytes),
+
+ TP_STRUCT__entry(__field(const void *, ptr)
+ __field(struct alloc_tag *, tag)
+ __field(size_t, bytes)
+ ),
+
+ TP_fast_assign(__entry->ptr = ptr;
+ __entry->tag = tag;
+ __entry->bytes = bytes;
+ ),
+
+ TP_printk("ptr %p, tag %p, bytes %zu",
+ __entry->ptr,
+ __entry->tag,
+ __entry->bytes
+ )
+);
+
+#endif /* _TRACE_ALLOC_TAG_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>
diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c
index 82e2c3448dcf..ca2412a67312 100644
--- a/mm/alloc_tag.c
+++ b/mm/alloc_tag.c
@@ -18,6 +18,9 @@
#include <linux/kmemleak.h>
#include <uapi/linux/alloc_tag.h>
+#define CREATE_TRACE_POINTS
+#include <trace/events/alloc_tag.h>
+
#include "internal.h"
#include "page_alloc.h"
@@ -54,6 +57,9 @@ EXPORT_SYMBOL(mem_alloc_profiling_key);
DEFINE_STATIC_KEY_FALSE(mem_profiling_compressed);
+DEFINE_STATIC_KEY_FALSE(alloc_tag_trace_key);
+EXPORT_SYMBOL(alloc_tag_trace_key);
+
struct alloc_tag_kernel_section kernel_tags = { NULL, 0 };
unsigned long alloc_tag_ref_mask;
int alloc_tag_ref_offs;
@@ -484,6 +490,28 @@ static const struct proc_ops allocinfo_proc_ops = {
#endif
};
+void __alloc_tag_trace_hit(struct alloc_tag *tag)
+{
+ if (unlikely(!tag))
+ return;
+ trace_alloc_tag_hit(tag);
+}
+EXPORT_SYMBOL(__alloc_tag_trace_hit);
+
+void alloc_tag_trace_mem_alloc(const void *ptr, struct alloc_tag *tag,
+ size_t bytes)
+{
+ trace_alloc_tag_mem_alloced(ptr, tag, bytes);
+}
+EXPORT_SYMBOL(alloc_tag_trace_mem_alloc);
+
+void alloc_tag_trace_mem_free(const void *ptr, struct alloc_tag *tag,
+ size_t bytes)
+{
+ trace_alloc_tag_mem_freed(ptr, tag, bytes);
+}
+EXPORT_SYMBOL(alloc_tag_trace_mem_free);
+
size_t alloc_tag_top_users(struct codetag_bytes *tags, size_t count, bool can_sleep)
{
struct codetag_iterator iter;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7682aecc2c07..5e3e411d4ffe 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1239,7 +1239,7 @@ void __pgalloc_tag_add(struct page *page, struct task_struct *task,
union codetag_ref ref;
if (likely(get_page_tag_ref(page, &ref, &handle))) {
- alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr);
+ alloc_tag_add(&ref, task->alloc_tag, PAGE_SIZE * nr, page);
update_page_tag_ref(handle, &ref);
put_page_tag_ref(handle);
} else {
@@ -1268,7 +1268,7 @@ void __pgalloc_tag_sub(struct page *page, unsigned int nr)
union codetag_ref ref;
if (get_page_tag_ref(page, &ref, &handle)) {
- alloc_tag_sub(&ref, PAGE_SIZE * nr);
+ alloc_tag_sub(&ref, PAGE_SIZE * nr, page);
update_page_tag_ref(handle, &ref);
put_page_tag_ref(handle);
}
diff --git a/mm/percpu.c b/mm/percpu.c
index 3eff382e565a..12b6c97d1596 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1695,15 +1695,19 @@ static void pcpu_alloc_tag_alloc_hook(struct pcpu_chunk *chunk, int off,
size_t size)
{
if (mem_alloc_profiling_enabled() && likely(chunk->obj_exts)) {
- alloc_tag_add(&chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].tag,
- current->alloc_tag, size);
+ union codetag_ref *ref = &chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].tag;
+
+ alloc_tag_add(ref, current->alloc_tag, size, ref);
}
}
static void pcpu_alloc_tag_free_hook(struct pcpu_chunk *chunk, int off, size_t size)
{
- if (mem_alloc_profiling_enabled() && likely(chunk->obj_exts))
- alloc_tag_sub(&chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].tag, size);
+ if (mem_alloc_profiling_enabled() && likely(chunk->obj_exts)) {
+ union codetag_ref *ref = &chunk->obj_exts[off >> PCPU_MIN_ALLOC_SHIFT].tag;
+
+ alloc_tag_sub(ref, size, ref);
+ }
}
#else
static void pcpu_alloc_tag_alloc_hook(struct pcpu_chunk *chunk, int off,
diff --git a/mm/slub.c b/mm/slub.c
index 544cff39762c..a866576ccb98 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2404,7 +2404,7 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,
obj_ext = slab_obj_ext(s, slab, obj_exts, object);
ref = slab_obj_ext_codetag_ref(slab, obj_ext);
- alloc_tag_add(ref, current->alloc_tag, s->size);
+ alloc_tag_add(ref, current->alloc_tag, s->size, ref);
put_slab_obj_exts(obj_exts);
} else {
@@ -2444,9 +2444,11 @@ __alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p
get_slab_obj_exts(obj_exts);
for (int i = 0; i < objects; i++) {
struct slabobj_ext *ext;
+ union codetag_ref *ref;
ext = slab_obj_ext(s, slab, obj_exts, p[i]);
- alloc_tag_sub(slab_obj_ext_codetag_ref(slab, ext), s->size);
+ ref = slab_obj_ext_codetag_ref(slab, ext);
+ alloc_tag_sub(ref, s->size, ref);
}
put_slab_obj_exts(obj_exts);
}
--
2.56.0.385.gd3acb90ef8-goog
^ permalink raw reply [flat|nested] 5+ messages in thread* [PATCH v2 2/4] alloc_tag: Introduce IOCTLs to toggle allocation tracepoints
2026-10-07 22:39 [PATCH v2 0/4] alloc_tag: Introduce selective tracing for MAP Abhishek Bapat
2026-10-07 22:39 ` [PATCH v2 1/4] alloc_tag: Add trace events for tracing allocations Abhishek Bapat
@ 2026-10-07 22:40 ` Abhishek Bapat
2026-10-07 22:40 ` [PATCH v2 3/4] alloc_tag: Extend allocinfo_filter to support tracing queries Abhishek Bapat
2026-10-07 22:40 ` [PATCH v2 4/4] alloc_tag: Add a test for trace state toggle and filtering Abhishek Bapat
3 siblings, 0 replies; 5+ messages in thread
From: Abhishek Bapat @ 2026-10-07 22:40 UTC (permalink / raw)
To: Suren Baghdasaryan, Hao Ge, Andrew Morton
Cc: linux-kernel, linux-mm, linux-trace-kernel, Abhishek Bapat
Introduce a new IOCTL (`ALLOCINFO_IOC_TOGGLE_TRACE`) to selectively
toggle tracing on allocation call sites. Userspace tools can use the
existing filtering mechanism to specify the set of tags to toggle
tracing for.
To facilitate low overhead execution for non-targeted call sites, add a
new `CODETAG_FLAG_TRACE_ON` flag to `struct codetag` to track per-site
activation. Protect these conditional branch evaluations using the global
`alloc_tag_trace_key` static branch and an inline static key check
pattern in the allocator hooks (`alloc_tag_add`, `alloc_tag_sub`, etc).
This ensures that the trace events are entirely skipped when no
allocation call sites are being actively traced, leaving only a NOP on
the allocation fast path.
Signed-off-by: Abhishek Bapat <abhishekbapat@google.com>
---
Documentation/mm/allocation-profiling.rst | 20 ++++
include/linux/alloc_tag.h | 47 +++++---
include/linux/codetag.h | 5 +-
include/uapi/linux/alloc_tag.h | 13 +++
mm/alloc_tag.c | 128 ++++++++++++++++++++--
5 files changed, 187 insertions(+), 26 deletions(-)
diff --git a/Documentation/mm/allocation-profiling.rst b/Documentation/mm/allocation-profiling.rst
index b241450394df..63b668466342 100644
--- a/Documentation/mm/allocation-profiling.rst
+++ b/Documentation/mm/allocation-profiling.rst
@@ -149,6 +149,26 @@ expose the full call stack and the lifetime of individual allocations:
- slab and percpu: the address of the object's `codetag_ref`
- page allocator: the `struct page` pointer of the head page
+Events are only emitted for tags that have tracing turned on and while profiling
+is enabled. When no tag is traced, the hooks are behind a static branch.
+
+Enabling Tracing
+----------------
+
+Tracing is toggled on and off per tag with the `ALLOCINFO_IOC_TOGGLE_TRACE`
+ioctl on `/proc/allocinfo`. It takes the same filter as used by
+`ALLOCINFO_IOC_GET_AT`; an empty mask selects all tags. Size limits in the
+filter are checked once, against the tag's size at the time of the call. Tags
+already in the requested state are skipped and a -ENOENT is returned if no
+tag matched.
+
+Tracing is turned off for a module's tags when the module is unloaded.
+
+Memory allocated before a tag was enabled has no alloc event but will still
+produce a free event. Likewise, memory alive when tag is disabled will not
+produce a free event. Tools should expect unmatched frees after enabling and
+missing frees after disabling.
+
Correlating the events
----------------------
diff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h
index 49825177d8c8..94697b28053a 100644
--- a/include/linux/alloc_tag.h
+++ b/include/linux/alloc_tag.h
@@ -136,9 +136,36 @@ static inline bool mem_alloc_profiling_enabled(void)
&mem_alloc_profiling_key);
}
-static inline bool alloc_tag_trace_enabled(void)
+static inline void alloc_tag_set_inaccurate(struct alloc_tag *tag)
{
- return static_branch_unlikely(&alloc_tag_trace_key);
+ atomic_or(CODETAG_FLAG_INACCURATE, &tag->ct.flags);
+}
+
+static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag)
+{
+ return !!(atomic_read(&tag->ct.flags) & CODETAG_FLAG_INACCURATE);
+}
+
+static inline void alloc_tag_set_traced(struct alloc_tag *tag)
+{
+ atomic_or(CODETAG_FLAG_TRACE_ON, &tag->ct.flags);
+}
+
+static inline void alloc_tag_clear_traced(struct alloc_tag *tag)
+{
+ atomic_andnot(CODETAG_FLAG_TRACE_ON, &tag->ct.flags);
+}
+
+static inline bool alloc_tag_is_traced(const struct alloc_tag *tag)
+{
+ return !!(atomic_read(&tag->ct.flags) & CODETAG_FLAG_TRACE_ON);
+}
+
+static inline bool alloc_tag_trace_enabled(const struct alloc_tag *tag)
+{
+ if (static_branch_unlikely(&alloc_tag_trace_key))
+ return tag && alloc_tag_is_traced(tag);
+ return false;
}
void alloc_tag_trace_mem_alloc(const void *ptr, struct alloc_tag *tag,
@@ -151,7 +178,7 @@ void __alloc_tag_trace_hit(struct alloc_tag *tag);
static __always_inline void alloc_tag_trace_hit(struct alloc_tag *tag)
{
- if (alloc_tag_trace_enabled())
+ if (alloc_tag_trace_enabled(tag))
__alloc_tag_trace_hit(tag);
}
@@ -225,7 +252,7 @@ static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag,
if (likely(alloc_tag_ref_set(ref, tag))) {
this_cpu_add(tag->counters->bytes, bytes);
- if (alloc_tag_trace_enabled())
+ if (alloc_tag_trace_enabled(tag))
/* Trace successful allocs with their unique ptr */
alloc_tag_trace_mem_alloc(ptr, tag, bytes);
}
@@ -249,23 +276,13 @@ static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes, const voi
this_cpu_sub(tag->counters->bytes, bytes);
this_cpu_dec(tag->counters->calls);
- if (alloc_tag_trace_enabled())
+ if (alloc_tag_trace_enabled(tag))
/* Trace frees with their unique ptr */
alloc_tag_trace_mem_free(ptr, tag, bytes);
ref->ct = NULL;
}
-static inline void alloc_tag_set_inaccurate(struct alloc_tag *tag)
-{
- tag->ct.flags |= CODETAG_FLAG_INACCURATE;
-}
-
-static inline bool alloc_tag_is_inaccurate(struct alloc_tag *tag)
-{
- return !!(tag->ct.flags & CODETAG_FLAG_INACCURATE);
-}
-
#define alloc_tag_record(p) ((p) = current->alloc_tag)
#else /* CONFIG_MEM_ALLOC_PROFILING */
diff --git a/include/linux/codetag.h b/include/linux/codetag.h
index a25a085c2df1..f728295d50c0 100644
--- a/include/linux/codetag.h
+++ b/include/linux/codetag.h
@@ -18,6 +18,7 @@ struct module;
/* codetag flags */
#define CODETAG_FLAG_INACCURATE (1 << 0)
+#define CODETAG_FLAG_TRACE_ON (1 << 1)
/*
* An instance of this structure is created in a special ELF section at every
@@ -25,7 +26,7 @@ struct module;
* an array of these.
*/
struct codetag {
- unsigned int flags;
+ atomic_t flags;
unsigned int lineno;
const char *modname;
const char *function;
@@ -71,7 +72,7 @@ struct codetag_iterator {
.function = __func__, \
.filename = __FILE__, \
.lineno = __LINE__, \
- .flags = 0, \
+ .flags = ATOMIC_INIT(0), \
}
void codetag_lock_module_list(struct codetag_type *cttype);
diff --git a/include/uapi/linux/alloc_tag.h b/include/uapi/linux/alloc_tag.h
index 7d4618bea043..dafcba2f7e2c 100644
--- a/include/uapi/linux/alloc_tag.h
+++ b/include/uapi/linux/alloc_tag.h
@@ -85,9 +85,20 @@ struct allocinfo_get_at {
struct allocinfo_tag_data data;
};
+struct allocinfo_toggle_traces {
+ /* inputs */
+ /*
+ * Tags matching the filter are toggled; an empty mask selects all tags.
+ * Size criteria are checked once, against the tag's size at call time.
+ */
+ struct allocinfo_filter filter;
+ __u64 enable;
+};
+
#define _ALLOCINFO_IOC_CONTENT_ID 0
#define _ALLOCINFO_IOC_GET_AT 1
#define _ALLOCINFO_IOC_GET_NEXT 2
+#define _ALLOCINFO_IOC_TOGGLE_TRACE 3
#define ALLOCINFO_IOC_BASE 0xA6
#define ALLOCINFO_IOC_CONTENT_ID _IOR(ALLOCINFO_IOC_BASE, _ALLOCINFO_IOC_CONTENT_ID, \
@@ -96,5 +107,7 @@ struct allocinfo_get_at {
struct allocinfo_get_at)
#define ALLOCINFO_IOC_GET_NEXT _IOR(ALLOCINFO_IOC_BASE, _ALLOCINFO_IOC_GET_NEXT, \
struct allocinfo_tag_data)
+#define ALLOCINFO_IOC_TOGGLE_TRACE _IOW(ALLOCINFO_IOC_BASE, _ALLOCINFO_IOC_TOGGLE_TRACE, \
+ struct allocinfo_toggle_traces)
#endif /* _UAPI_ALLOC_TAG_H */
diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c
index ca2412a67312..262f00f2bba9 100644
--- a/mm/alloc_tag.c
+++ b/mm/alloc_tag.c
@@ -60,6 +60,15 @@ DEFINE_STATIC_KEY_FALSE(mem_profiling_compressed);
DEFINE_STATIC_KEY_FALSE(alloc_tag_trace_key);
EXPORT_SYMBOL(alloc_tag_trace_key);
+static atomic_t alloc_tag_trace_cnt = ATOMIC_INIT(0);
+
+/*
+ * As `codetag_lock_module_list` is a read lock, we need an additional mutex
+ * to protect against the race conditions involved in the alloc tag trace
+ * toggle path.
+ */
+static DEFINE_MUTEX(alloc_tag_trace_mutex);
+
struct alloc_tag_kernel_section kernel_tags = { NULL, 0 };
unsigned long alloc_tag_ref_mask;
int alloc_tag_ref_offs;
@@ -296,7 +305,7 @@ static bool matches_filter(struct codetag *ct, struct allocinfo_filter *filter,
return false;
if (filter->mask & ALLOCINFO_FILTER_MASK_INACCURATE) {
- inaccurate = !!(ct->flags & CODETAG_FLAG_INACCURATE);
+ inaccurate = alloc_tag_is_inaccurate(ct_to_alloc_tag(ct));
if (inaccurate != !!(filter->inaccurate))
return false;
}
@@ -317,6 +326,23 @@ static bool matches_filter(struct codetag *ct, struct allocinfo_filter *filter,
return true;
}
+/*
+ * Checks that a user supplied filter only uses known fields and that its size
+ * range, if any, is not inverted.
+ */
+static bool allocinfo_filter_valid(const struct allocinfo_filter *filter)
+{
+ if (filter->mask & ~ALLOCINFO_FILTER_MASKS)
+ return false;
+
+ if ((filter->mask & ALLOCINFO_FILTER_MASK_MIN_SIZE) &&
+ (filter->mask & ALLOCINFO_FILTER_MASK_MAX_SIZE) &&
+ filter->min_size > filter->max_size)
+ return false;
+
+ return true;
+}
+
/*
* Seeks the ioctl iterator to the specified 0-indexed tag position, reads its
* profiling data and returns it to userspace.
@@ -333,12 +359,7 @@ static int allocinfo_ioctl_get_at(struct seq_file *m, void __user *arg)
if (copy_from_user(¶ms, arg, sizeof(params)))
return -EFAULT;
- if (params.filter.mask & ~ALLOCINFO_FILTER_MASKS)
- return -EINVAL;
-
- if ((params.filter.mask & ALLOCINFO_FILTER_MASK_MIN_SIZE) &&
- (params.filter.mask & ALLOCINFO_FILTER_MASK_MAX_SIZE) &&
- params.filter.min_size > params.filter.max_size)
+ if (!allocinfo_filter_valid(¶ms.filter))
return -EINVAL;
priv = m->private;
@@ -443,6 +464,75 @@ static int allocinfo_ioctl_get_next(struct seq_file *m, void __user *arg)
return ret;
}
+static void alloc_tag_trace_toggle(struct alloc_tag *tag, bool enable)
+{
+ if (enable) {
+ if (alloc_tag_is_traced(tag))
+ return;
+
+ alloc_tag_set_traced(tag);
+ if (atomic_fetch_inc(&alloc_tag_trace_cnt) == 0)
+ static_branch_enable(&alloc_tag_trace_key);
+ } else {
+ if (!alloc_tag_is_traced(tag))
+ return;
+
+ alloc_tag_clear_traced(tag);
+ if (atomic_dec_and_test(&alloc_tag_trace_cnt))
+ static_branch_disable(&alloc_tag_trace_key);
+ }
+}
+
+/*
+ * Toggles tracing on every allocation tag that matches the user supplied
+ * filter. An empty filter mask selects all tags, same as for
+ * ALLOCINFO_IOC_GET_AT. Tags already in the requested state are not an error.
+ */
+static int allocinfo_ioctl_toggle_trace(struct seq_file *m, void __user *arg)
+{
+ struct allocinfo_toggle_traces params;
+ struct codetag_iterator iter;
+ struct codetag *ct;
+ struct alloc_tag_counters counters;
+ bool fetched_counters;
+ int matches = 0, ret;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ if (copy_from_user(¶ms, arg, sizeof(params)))
+ return -EFAULT;
+
+ if (!allocinfo_filter_valid(¶ms.filter))
+ return -EINVAL;
+
+ codetag_lock_module_list(alloc_tag_cttype);
+
+ iter = codetag_get_ct_iter(alloc_tag_cttype);
+
+ /* Toggle tracing on all codetags that match */
+ while ((ct = codetag_next_ct(&iter))) {
+ fetched_counters = false;
+ if (matches_filter(ct, ¶ms.filter, &counters, &fetched_counters)) {
+ matches++;
+
+ mutex_lock(&alloc_tag_trace_mutex);
+ alloc_tag_trace_toggle(ct_to_alloc_tag(ct), !!params.enable);
+ mutex_unlock(&alloc_tag_trace_mutex);
+ }
+ }
+
+ if (matches == 0)
+ /* Nothing matched the filter */
+ ret = -ENOENT;
+ else
+ ret = 0;
+
+ codetag_unlock_module_list(alloc_tag_cttype);
+
+ return ret;
+}
+
/*
* Entry point ioctl function for /proc/allocinfo routing requests to fetch the
* layout content ID, seek to a specific tag, or read sequential tags.
@@ -463,6 +553,9 @@ static long allocinfo_ioctl(struct file *file, unsigned int cmd,
case ALLOCINFO_IOC_GET_NEXT:
ret = allocinfo_ioctl_get_next(file->private_data, arg);
break;
+ case ALLOCINFO_IOC_TOGGLE_TRACE:
+ ret = allocinfo_ioctl_toggle_trace(file->private_data, arg);
+ break;
default:
ret = -ENOIOCTLCMD;
break;
@@ -492,8 +585,6 @@ static const struct proc_ops allocinfo_proc_ops = {
void __alloc_tag_trace_hit(struct alloc_tag *tag)
{
- if (unlikely(!tag))
- return;
trace_alloc_tag_hit(tag);
}
EXPORT_SYMBOL(__alloc_tag_trace_hit);
@@ -1031,6 +1122,24 @@ static int load_module(struct module *mod, struct codetag *start, struct codetag
return 0;
}
+static void unload_module(struct module *mod, struct codetag *start, struct codetag *stop)
+{
+ struct alloc_tag *start_tag = ct_to_alloc_tag(start);
+ struct alloc_tag *stop_tag = ct_to_alloc_tag(stop);
+ struct alloc_tag *tag;
+
+ /*
+ * Turn tracing off for the tags of the module being unloaded. Without
+ * this, `alloc_tag_trace_cnt` would never reach zero and tracing would
+ * stay enabled forever.
+ *
+ * `alloc_tag_trace_mutex` is not needed here as this code path is
+ * protected by a `down_write(&cttype->mod_lock)`.
+ */
+ for (tag = start_tag; tag < stop_tag; tag++)
+ alloc_tag_trace_toggle(tag, false);
+}
+
static void replace_module(struct module *mod, struct module *new_mod)
{
MA_STATE(mas, &mod_area_mt, 0, module_tags.size);
@@ -1357,6 +1466,7 @@ static int __init alloc_tag_init(void)
.alloc_section_mem = reserve_module_tags,
.free_section_mem = release_module_tags,
.module_load = load_module,
+ .module_unload = unload_module,
.module_replaced = replace_module,
#endif
};
--
2.56.0.385.gd3acb90ef8-goog
^ permalink raw reply [flat|nested] 5+ messages in thread* [PATCH v2 4/4] alloc_tag: Add a test for trace state toggle and filtering
2026-10-07 22:39 [PATCH v2 0/4] alloc_tag: Introduce selective tracing for MAP Abhishek Bapat
` (2 preceding siblings ...)
2026-10-07 22:40 ` [PATCH v2 3/4] alloc_tag: Extend allocinfo_filter to support tracing queries Abhishek Bapat
@ 2026-10-07 22:40 ` Abhishek Bapat
3 siblings, 0 replies; 5+ messages in thread
From: Abhishek Bapat @ 2026-10-07 22:40 UTC (permalink / raw)
To: Suren Baghdasaryan, Hao Ge, Andrew Morton
Cc: linux-kernel, linux-mm, linux-trace-kernel, Abhishek Bapat
Following the introduction of the ALLOCINFO_IOC_TOGGLE_TRACE IOCTL and
ALLOCINFO_FILTER_MASK_TRACE_ON filters for selective memory allocation
tracing, update the kselftests to validate this behaviour.
Introduce `test_tracing_toggle_and_filter`, which validates the
architecture by:
1. Dynamically flipping trace execution state for a designated allocation.
2. Query the same tag again, and check that the returned tag reports the
new state in its `trace_on` field.
3. Restore the tag's original trace state, also on failure, so the test
does not leave tracing changed on the system.
The test uses `dup_mm()` function name with the function filter in the
IOCTL to run the above steps. If the `dup_mm()` tag is not found, the
test is skipped.
Signed-off-by: Abhishek Bapat <abhishekbapat@google.com>
---
.../alloc_tag/allocinfo_ioctl_test.c | 113 +++++++++++++++++-
1 file changed, 110 insertions(+), 3 deletions(-)
diff --git a/tools/testing/selftests/alloc_tag/allocinfo_ioctl_test.c b/tools/testing/selftests/alloc_tag/allocinfo_ioctl_test.c
index 74fd64b2370c..eb52ca1a1dc4 100644
--- a/tools/testing/selftests/alloc_tag/allocinfo_ioctl_test.c
+++ b/tools/testing/selftests/alloc_tag/allocinfo_ioctl_test.c
@@ -48,6 +48,11 @@ static inline int __allocinfo_get_next(int dev_fd, struct allocinfo_tag_data *pa
return ioctl(dev_fd, ALLOCINFO_IOC_GET_NEXT, params);
}
+static inline int __allocinfo_toggle_trace(int dev_fd, struct allocinfo_toggle_traces *params)
+{
+ return ioctl(dev_fd, ALLOCINFO_IOC_TOGGLE_TRACE, params);
+}
+
static bool match_entry(const struct allocinfo_tag_data *procfs_entry,
const struct allocinfo_tag_data *tag_data,
bool match_bytes, bool match_calls, bool match_lineno,
@@ -289,6 +294,8 @@ static int run_filter_test(const struct allocinfo_filter *filter)
return ret;
}
+static const char *target_test_function = "dup_mm";
+
static int test_filename_filter(void)
{
struct allocinfo_filter filter;
@@ -304,11 +311,10 @@ static int test_filename_filter(void)
static int test_function_filter(void)
{
struct allocinfo_filter filter;
- const char *target_function = "dup_mm";
memset(&filter, 0, sizeof(filter));
filter.mask |= ALLOCINFO_FILTER_MASK_FUNCTION;
- strncpy(filter.fields.function, target_function, ALLOCINFO_STR_SIZE);
+ strncpy(filter.fields.function, target_test_function, ALLOCINFO_STR_SIZE);
return run_filter_test(&filter);
}
@@ -514,11 +520,106 @@ static int test_lineno_filter(void)
return ret;
}
+static enum ioctl_ret toggle_trace(struct allocinfo_tag *target_tag,
+ bool enable)
+{
+ int fd;
+ struct allocinfo_toggle_traces toggle_params;
+
+ fd = open(ALLOCINFO_PROC, O_RDONLY);
+ if (fd < 0) {
+ ksft_print_msg("Failed to open " ALLOCINFO_PROC ": %s\n", strerror(errno));
+ return IOCTL_FAILURE;
+ }
+
+ memset(&toggle_params, 0, sizeof(toggle_params));
+ toggle_params.filter.mask = ALLOCINFO_FILTER_MASK_MODNAME | ALLOCINFO_FILTER_MASK_FUNCTION |
+ ALLOCINFO_FILTER_MASK_FILENAME | ALLOCINFO_FILTER_MASK_LINENO;
+ toggle_params.filter.fields = *target_tag;
+ toggle_params.enable = enable;
+
+ if (__allocinfo_toggle_trace(fd, &toggle_params)) {
+ close(fd);
+ return IOCTL_FAILURE;
+ }
+
+ close(fd);
+ return IOCTL_SUCCESS;
+}
+
+static int test_tracing_toggle_and_filter(void)
+{
+ struct allocinfo_filter filter = { 0 };
+ enum ioctl_ret ioctl_status;
+ int ret = KSFT_PASS;
+ bool initial_state, target_state;
+ struct allocinfo_tag target_tag;
+ struct allocinfo_tag_data_vec *tags = calloc(1, sizeof(*tags));
+
+ if (!tags) {
+ ksft_print_msg("Memory allocation failed.\n");
+ return KSFT_FAIL;
+ }
+
+ filter.mask |= ALLOCINFO_FILTER_MASK_FUNCTION;
+ strncpy(filter.fields.function, target_test_function, ALLOCINFO_STR_SIZE);
+
+ ioctl_status = get_filtered_ioctl_entries(tags, &filter, 0);
+ if (ioctl_status != IOCTL_SUCCESS || tags->count == 0) {
+ ksft_print_msg("Could not retrieve IOCTL entries for %s\n", target_test_function);
+ ret = KSFT_SKIP;
+ goto exit;
+ }
+
+ target_tag = tags->tag[0].tag;
+ initial_state = tags->tag[0].counter.trace_on;
+ target_state = !initial_state;
+
+ ioctl_status = toggle_trace(&target_tag, target_state);
+ if (ioctl_status != IOCTL_SUCCESS) {
+ ksft_print_msg("Failed to toggle tracing\n");
+ ret = KSFT_FAIL;
+ goto exit;
+ }
+
+ filter.mask |= ALLOCINFO_FILTER_MASK_TRACE_ON;
+ filter.tracing = target_state;
+
+ ioctl_status = get_filtered_ioctl_entries(tags, &filter, 0);
+ if (ioctl_status != IOCTL_SUCCESS) {
+ ksft_print_msg("Error retrieving IOCTL entries with trace filter.\n");
+ ret = KSFT_FAIL;
+ goto exit_revert;
+ }
+
+ if (tags->count != 1) {
+ ksft_print_msg("Expected exactly 1 entry, but got %llu\n", tags->count);
+ ret = KSFT_FAIL;
+ goto exit_revert;
+ }
+
+ if (tags->tag[0].counter.trace_on != target_state) {
+ ksft_print_msg("Entry returned by trace filter does not match target state\n");
+ ret = KSFT_FAIL;
+ }
+
+exit_revert:
+ ioctl_status = toggle_trace(&target_tag, initial_state);
+ if (ioctl_status != IOCTL_SUCCESS) {
+ ksft_print_msg("Failed to revert tracing to initial state\n");
+ ret = KSFT_FAIL;
+ }
+
+exit:
+ free(tags);
+ return ret;
+}
+
int main(int argc, char *argv[])
{
int ret;
- ksft_set_plan(4);
+ ksft_set_plan(5);
ret = test_filename_filter();
if (ret == KSFT_SKIP)
@@ -526,6 +627,12 @@ int main(int argc, char *argv[])
else
ksft_test_result(ret == KSFT_PASS, "test_filename_filter\n");
+ ret = test_tracing_toggle_and_filter();
+ if (ret == KSFT_SKIP)
+ ksft_test_result_skip("Skipping test_tracing_toggle_and_filter\n");
+ else
+ ksft_test_result(ret == KSFT_PASS, "test_tracing_toggle_and_filter\n");
+
ret = test_function_filter();
if (ret == KSFT_SKIP)
ksft_test_result_skip("Skipping test_function_filter\n");
--
2.56.0.385.gd3acb90ef8-goog
^ permalink raw reply [flat|nested] 5+ messages in thread