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([2a02:6b6f:e759:7e00:1047:5c2a:74d8:1f23]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3e900d8f0e9sm14410982f8f.35.2025.09.16.14.11.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 16 Sep 2025 14:11:27 -0700 (PDT) Message-ID: Date: Tue, 16 Sep 2025 22:11:27 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 1/1] alloc_tag: mark inaccurate allocation counters in /proc/allocinfo output Content-Language: en-GB To: Suren Baghdasaryan , Vlastimil Babka Cc: akpm@linux-foundation.org, kent.overstreet@linux.dev, hannes@cmpxchg.org, rientjes@google.com, roman.gushchin@linux.dev, harry.yoo@oracle.com, shakeel.butt@linux.dev, 00107082@163.com, pyyjason@gmail.com, pasha.tatashin@soleen.com, souravpanda@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20250915230224.4115531-1-surenb@google.com> <2d8eb571-6d76-4a9e-8d08-0da251a73f33@suse.cz> From: Usama Arif In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 16/09/2025 16:51, Suren Baghdasaryan wrote: > On Tue, Sep 16, 2025 at 5:57 AM Vlastimil Babka wrote: >> >> On 9/16/25 01:02, Suren Baghdasaryan wrote: >>> While rare, memory allocation profiling can contain inaccurate counters >>> if slab object extension vector allocation fails. That allocation might >>> succeed later but prior to that, slab allocations that would have used >>> that object extension vector will not be accounted for. To indicate >>> incorrect counters, "accurate:no" marker is appended to the call site >>> line in the /proc/allocinfo output. >>> Bump up /proc/allocinfo version to reflect the change in the file format >>> and update documentation. >>> >>> Example output with invalid counters: >>> allocinfo - version: 2.0 >>> 0 0 arch/x86/kernel/kdebugfs.c:105 func:create_setup_data_nodes >>> 0 0 arch/x86/kernel/alternative.c:2090 func:alternatives_smp_module_add >>> 0 0 arch/x86/kernel/alternative.c:127 func:__its_alloc accurate:no >>> 0 0 arch/x86/kernel/fpu/regset.c:160 func:xstateregs_set >>> 0 0 arch/x86/kernel/fpu/xstate.c:1590 func:fpstate_realloc >>> 0 0 arch/x86/kernel/cpu/aperfmperf.c:379 func:arch_enable_hybrid_capacity_scale >>> 0 0 arch/x86/kernel/cpu/amd_cache_disable.c:258 func:init_amd_l3_attrs >>> 49152 48 arch/x86/kernel/cpu/mce/core.c:2709 func:mce_device_create accurate:no >>> 32768 1 arch/x86/kernel/cpu/mce/genpool.c:132 func:mce_gen_pool_create >>> 0 0 arch/x86/kernel/cpu/mce/amd.c:1341 func:mce_threshold_create_device >>> >>> Suggested-by: Johannes Weiner >>> Signed-off-by: Suren Baghdasaryan >>> Acked-by: Shakeel Butt >>> Acked-by: Usama Arif >>> Acked-by: Johannes Weiner >> >> With this format you could instead print the accumulated size of allocations >> that could not allocate their objext (for the given tag). It should be then >> an upper bound of the actual error, because obviously we cannot recognize >> moments where these allocations are freed - so we don't know for which tag >> to decrement. Maybe it could be more useful output than the yes/no >> information, although of course require more storage in struct codetag, so I >> don't know if it's worth it. > > Yeah, I'm reluctant to add more fields to the codetag and increase the > overhead until we have a usecases. If that happens and with the new > format we can add something like error_size: to indicate the > amount of the error. > >> >> Maybe a global counter of sum size for all these missed objexts could be >> also maintained, and that wouldn't be an upper bound but an actual current >> error, that is if we can precisely determine that when freeing an object, we >> don't have a tag to decrement because objext allocation had failed on it and >> thus that allocation had incremented this global error counter and it's >> correct to decrement it. > > That's a good idea and should be doable without too much overhead. Thanks! > For the UAPI... I think for this case IOCTL would work and the use > scenario would be that the user sees the "accurate:no" mark and issues > ioctl command to retrieve this global counter value. > Usama, since you initiated this feature request, do you think such a > counter would be useful? > hmm, I really dont like suggesting changing /proc/allocinfo as it will break parsers, but it might be better to put it there? If the value is in the file, I imagine people will be more prone to looking at it? I am not completely sure if everyone will do an ioctl to try and find this out? Especially if you just have infra that is just automatically collecting info from this file. >> >>> --- >>> Changes since v1[1]: >>> - Changed the marker from asterisk to accurate:no pair, per Andrew Morton >>> - Documented /proc/allocinfo v2 format >>> - Update the changelog >>> - Added Acked-by from v2 since the functionality is the same, >>> per Shakeel Butt, Usama Arif and Johannes Weiner >>> >>> [1] https://lore.kernel.org/all/20250909234942.1104356-1-surenb@google.com/ >>> >>> Documentation/filesystems/proc.rst | 4 ++++ >>> include/linux/alloc_tag.h | 12 ++++++++++++ >>> include/linux/codetag.h | 5 ++++- >>> lib/alloc_tag.c | 4 +++- >>> mm/slub.c | 2 ++ >>> 5 files changed, 25 insertions(+), 2 deletions(-) >>> >>> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst >>> index 915a3e44bc12..1776a06571c2 100644 >>> --- a/Documentation/filesystems/proc.rst >>> +++ b/Documentation/filesystems/proc.rst >>> @@ -1009,6 +1009,10 @@ number, module (if originates from a loadable module) and the function calling >>> the allocation. The number of bytes allocated and number of calls at each >>> location are reported. The first line indicates the version of the file, the >>> second line is the header listing fields in the file. >>> +If file version is 2.0 or higher then each line may contain additional >>> +: pairs representing extra information about the call site. >>> +For example if the counters are not accurate, the line will be appended with >>> +"accurate:no" pair. >>> >>> Example output. >>> >>> diff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h >>> index 9ef2633e2c08..d40ac39bfbe8 100644 >>> --- a/include/linux/alloc_tag.h >>> +++ b/include/linux/alloc_tag.h >>> @@ -221,6 +221,16 @@ static inline void alloc_tag_sub(union codetag_ref *ref, size_t 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 */ >>> @@ -230,6 +240,8 @@ static inline bool mem_alloc_profiling_enabled(void) { return false; } >>> 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) {} >>> +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_record(p) do {} while (0) >>> >>> #endif /* CONFIG_MEM_ALLOC_PROFILING */ >>> diff --git a/include/linux/codetag.h b/include/linux/codetag.h >>> index 457ed8fd3214..8ea2a5f7c98a 100644 >>> --- a/include/linux/codetag.h >>> +++ b/include/linux/codetag.h >>> @@ -16,13 +16,16 @@ struct module; >>> #define CODETAG_SECTION_START_PREFIX "__start_" >>> #define CODETAG_SECTION_STOP_PREFIX "__stop_" >>> >>> +/* codetag flags */ >>> +#define CODETAG_FLAG_INACCURATE (1 << 0) >>> + >>> /* >>> * An instance of this structure is created in a special ELF section at every >>> * code location being tagged. At runtime, the special section is treated as >>> * an array of these. >>> */ >>> struct codetag { >>> - unsigned int flags; /* used in later patches */ >>> + unsigned int flags; >>> unsigned int lineno; >>> const char *modname; >>> const char *function; >>> diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c >>> index 79891528e7b6..12ff80bbbd22 100644 >>> --- a/lib/alloc_tag.c >>> +++ b/lib/alloc_tag.c >>> @@ -80,7 +80,7 @@ static void allocinfo_stop(struct seq_file *m, void *arg) >>> static void print_allocinfo_header(struct seq_buf *buf) >>> { >>> /* Output format version, so we can change it. */ >>> - seq_buf_printf(buf, "allocinfo - version: 1.0\n"); >>> + seq_buf_printf(buf, "allocinfo - version: 2.0\n"); >>> seq_buf_printf(buf, "# \n"); >>> } >>> >>> @@ -92,6 +92,8 @@ static void alloc_tag_to_text(struct seq_buf *out, struct codetag *ct) >>> >>> seq_buf_printf(out, "%12lli %8llu ", bytes, counter.calls); >>> codetag_to_text(out, ct); >>> + if (unlikely(alloc_tag_is_inaccurate(tag))) >>> + seq_buf_printf(out, " accurate:no"); >>> seq_buf_putc(out, ' '); >>> seq_buf_putc(out, '\n'); >>> } >>> diff --git a/mm/slub.c b/mm/slub.c >>> index af343ca570b5..9c04f29ee8de 100644 >>> --- a/mm/slub.c >>> +++ b/mm/slub.c >>> @@ -2143,6 +2143,8 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags) >>> */ >>> if (likely(obj_exts)) >>> alloc_tag_add(&obj_exts->ref, current->alloc_tag, s->size); >>> + else >>> + alloc_tag_set_inaccurate(current->alloc_tag); >>> } >>> >>> static inline void >>