On Sat, Oct 17, 2026 at 5:33 AM Suren Baghdasaryan <[email protected]> wrote:
>
> On Tue, Oct 13, 2026 at 10:12 AM Hao Ge <[email protected]> wrote:
> >
> > Hi Abhishek
> >
> >
> >
> > On 2026/10/8 06:39, Abhishek Bapat wrote:
> > > 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 <[email protected]>
> >
> > Acked-by: Hao Ge <[email protected]>
>
> Acked-by: Suren Baghdasaryan <[email protected]>
>
> >
> > > ---
> > > 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))
>
> nit: Is there a case when we pass tag=NULL here?
>
Yes, sashiko brought this up during my local review before I sent the
patch. If MAP CONFIG option is enabled but the kernel is booted with
the sysctl set to 0, rhashtable_init() eventually calls
alloc_hooks_tag(). mem_alloc_profiling_enabled() returns false and
alloc_tag_save() is skipped leaving ht->alloc_tag to NULL. If the
sysctl value is later enabled, alloc_hooks_tag() will be called with
ht->alloc_tag set = NULL leading to a NULL pointer exception in
alloc_tag_trace_hit(). Which is why the NULL check is required.
> > > + 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);
> > > }
