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Wed, 23 Sep 2026 09:55:49 +0000 X-Mizu-Trace-ID: 585754956f1076bd X-Migadu-Flow: FLOW_OUT Message-ID: Date: Wed, 23 Sep 2026 17:56:50 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/4] alloc_tag: Add trace events for tracing allocations To: Abhishek Bapat , Suren Baghdasaryan , Andrew Morton Cc: Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, Shuah Khan References: <06c3a9b52785e6968ea15709a55365b2342c7a15.1790025465.git.abhishekbapat@google.com> Content-Language: en-US From: Hao Ge In-Reply-To: <06c3a9b52785e6968ea15709a55365b2342c7a15.1790025465.git.abhishekbapat@google.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Stat-Signature: 4ztjp499j3mfizimoyz59ay4urux4hkr X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: D75BC1C0004 X-HE-Tag: 1790157350-842227 X-HE-Meta: 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 TZWLrLua EoEyzrvtddSqxmwuj9s7BBAAzvmMgh2J0pK9gu5r8BUz/TMonYXO/PHVv6UZODuT2vMhm02dK6tvg0vLaW0EQ4rCgdrVPJ7kqAvEytnJ37S5K+qusfdTEqzCorE7mXaeqOklvFdaJj67Fcj9Tx03o8xBJ41Nm7YIIH69woKA6iuJ0HqzIiRcU8q61e2EGwnmF4ivua/S9sSP+KGGfBdLLT5o8sDHA+yTYGPV5oZtREM3shO7+8lbacNqx68ZdO4MJtujhkCBjlL5C+XXRxCbKYQzRefYeKC272w5H9i9K3M18nFTP8GpFEmIgS5mBBMEgIFcJ5EacHQ3qYryfspop1LZ75lbUcZkcT7fsSVou9SB3zay9LxD6OqKD5Q== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Abhishek On 2026/9/22 05:26, 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 codetag_ref metadata pointer. > 3. `alloc_tag_mem_freed`: Fired in alloc_tag_sub right before memory is > freed, yielding the same codetag_ref 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 `codetag_ref` > 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 `codetag_ref`. The tool uses this reference to look up the > original allocation record, correlates the free, and safely retires > the tracking entry. > > 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. > Nore that the mechanism to enabl tag tracing is implemented in the next > patch, therefore for now, `alloc_tag_trace_key` stays always unset. > nit: s/Nore/Note/ s/enabl/enable > Signed-off-by: Abhishek Bapat > --- > MAINTAINERS | 1 + > include/linux/alloc_tag.h | 57 ++++++++++++--- > include/trace/events/alloc_tag.h | 122 +++++++++++++++++++++++++++++++ > mm/alloc_tag.c | 28 +++++++ > 4 files changed, 196 insertions(+), 12 deletions(-) > create mode 100644 include/trace/events/alloc_tag.h > > diff --git a/MAINTAINERS b/MAINTAINERS > index 24420a8c06d0..29e1f7915cb9 100644 > --- a/MAINTAINERS > +++ b/MAINTAINERS > @@ -17096,6 +17096,7 @@ 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..2994934cf44a 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(const struct alloc_tag *tag) > +{ > + return static_branch_unlikely(&alloc_tag_trace_key); > +} > + The tag parameter is unused here. Let's remove it for now and add it back when needed, to avoid the -Wno‑unused‑parameter warning. Some CI bots go through each patch one‑by‑one, so we can't leave warnings in intermediate commits. One other thought: what about adding a sysctl knob here? It would let users grab all alloc‑tag tracked allocations within a time window? Thanks Best Regards Hao > +void alloc_tag_trace_mem_alloc(union codetag_ref *ref, struct alloc_tag *tag, > + size_t bytes); > + > +void alloc_tag_trace_mem_free(union codetag_ref *ref, struct alloc_tag *tag, > + size_t bytes); > + > +void __alloc_tag_trace_hit(struct alloc_tag *tag); > + > +static inline void alloc_tag_trace_hit(struct alloc_tag *tag) > +{ > + if (alloc_tag_trace_enabled(tag)) > + __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) > @@ -200,8 +221,13 @@ static inline bool alloc_tag_ref_set(union codetag_ref *ref, struct alloc_tag *t > > static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag, size_t bytes) > { > - 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(tag)) > + /* Trace successful allocs with their unique ref */ > + alloc_tag_trace_mem_alloc(ref, tag, bytes); > + } > } > > static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes) > @@ -222,6 +248,10 @@ 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(tag)) > + /* Trace frees with their unique ref */ > + alloc_tag_trace_mem_free(ref, tag, bytes); > + > ref->ct = NULL; > } > > @@ -247,21 +277,24 @@ static inline void alloc_tag_add(union codetag_ref *ref, struct alloc_tag *tag, > static inline void alloc_tag_sub(union codetag_ref *ref, size_t bytes) {} > 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..af2182501864 > --- /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 > + > +/* > + * 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 `ref` pointer identifies the memory chunk for tracking its lifecycle > + * (e.g., matching it with alloc_tag_mem_freed). > + * > + * Because the kernel isolates active allocations within the task struct > + * (current->alloc_tag), this even 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(union codetag_ref *ref, struct alloc_tag *tag, size_t bytes), > + > + TP_ARGS(ref, tag, bytes), > + > + TP_STRUCT__entry( > + __field(union codetag_ref *, ref) > + __field(struct alloc_tag *, tag) > + __field(size_t, bytes) > + ), > + > + TP_fast_assign( > + __entry->ref = ref; > + __entry->tag = tag; > + __entry->bytes = bytes; > + ), > + > + TP_printk("reference %p, tag %p, bytes %zu", > + __entry->ref, > + __entry->tag, > + __entry->bytes > + ) > +); > + > +/* > + * alloc_tag_mem_freed event is generated immediately before memory is > + * freed. The `ref` pointer matches the one emitted during allocation, > + * allowing tools to match it to it's corresponding allocation and > + * call stack. > + */ > +TRACE_EVENT(alloc_tag_mem_freed, > + > + TP_PROTO(union codetag_ref *ref, struct alloc_tag *tag, size_t bytes), > + > + TP_ARGS(ref, tag, bytes), > + > + TP_STRUCT__entry( > + __field(union codetag_ref *, ref) > + __field(struct alloc_tag *, tag) > + __field(size_t, bytes) > + ), > + > + TP_fast_assign( > + __entry->ref = ref; > + __entry->tag = tag; > + __entry->bytes = bytes; > + ), > + > + TP_printk("reference %p, tag %p, bytes %zu", > + __entry->ref, > + __entry->tag, > + __entry->bytes > + ) > +); > + > +#endif /* _TRACE_ALLOC_TAG_H */ > + > +/* This part must be outside protection */ > +#include > diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c > index f30ef8dd24c7..a5339767efd5 100644 > --- a/mm/alloc_tag.c > +++ b/mm/alloc_tag.c > @@ -19,6 +19,9 @@ > #include > #include > > +#define CREATE_TRACE_POINTS > +#include > + > #include "internal.h" > #include "page_alloc.h" > > @@ -55,6 +58,9 @@ 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; > @@ -485,6 +491,28 @@ 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(union codetag_ref *ref, struct alloc_tag *tag, > + size_t bytes) > +{ > + trace_alloc_tag_mem_alloced(ref, tag, bytes); > +} > +EXPORT_SYMBOL(alloc_tag_trace_mem_alloc); > + > +void alloc_tag_trace_mem_free(union codetag_ref *ref, struct alloc_tag *tag, > + size_t bytes) > +{ > + trace_alloc_tag_mem_freed(ref, 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;