Re: [PATCH v3 20/35] lib: add codetag reference into slabobj_ext

Vlastimil Babka
2024-02-16T15:36:20Z

On 2/12/24 22:39, Suren Baghdasaryan wrote:
> To store code tag for every slab object, a codetag reference is embedded
> into slabobj_ext when CONFIG_MEM_ALLOC_PROFILING=y.
>
> Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> Co-developed-by: Kent Overstreet <kent.overstreet@linux.dev>
> Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
> ---
> include/linux/memcontrol.h | 5 +++++
> lib/Kconfig.debug | 1 +
> mm/slab.h | 4 ++++
> 3 files changed, 10 insertions(+)
>
> diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
> index f3584e98b640..2b010316016c 100644
> --- a/include/linux/memcontrol.h
> +++ b/include/linux/memcontrol.h
> @@ -1653,7 +1653,12 @@ unsigned long mem_cgroup_soft_limit_reclaim(pg_data_t *pgdat, int order,
> * if MEMCG_DATA_OBJEXTS is set.
> */
> struct slabobj_ext {
> +#ifdef CONFIG_MEMCG_KMEM
> struct obj_cgroup *objcg;
> +#endif
> +#ifdef CONFIG_MEM_ALLOC_PROFILING
> + union codetag_ref ref;
> +#endif
> } __aligned(8);

So this means that compiling with CONFIG_MEM_ALLOC_PROFILING will increase
the memory overhead of arrays allocated for CONFIG_MEMCG_KMEM, even if
allocation profiling itself is not enabled in runtime? Similar concern to
the unconditional page_ext usage, that this would hinder enabling in a
general distro kernel.

The unused field overhead would be smaller than currently page_ext, but
getting rid of it when alloc profiling is not enabled would be more work
than introducing an early boot param for the page_ext case. Could be however
solved similarly to how page_ext is populated dynamically at runtime.
Hopefully it wouldn't add noticeable cpu overhead.

> static inline void __inc_lruvec_kmem_state(void *p, enum node_stat_item idx)
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 7bbdb0ddb011..9ecfcdb54417 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -979,6 +979,7 @@ config MEM_ALLOC_PROFILING
> depends on !DEBUG_FORCE_WEAK_PER_CPU
> select CODE_TAGGING
> select PAGE_EXTENSION
> + select SLAB_OBJ_EXT
> help
> Track allocation source code and record total allocation size
> initiated at that code location. The mechanism can be used to track
> diff --git a/mm/slab.h b/mm/slab.h
> index 77cf7474fe46..224a4b2305fb 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -569,6 +569,10 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
>
> static inline bool need_slab_obj_ext(void)
> {
> +#ifdef CONFIG_MEM_ALLOC_PROFILING
> + if (mem_alloc_profiling_enabled())
> + return true;
> +#endif
> /*
> * CONFIG_MEMCG_KMEM creates vector of obj_cgroup objects conditionally
> * inside memcg_slab_post_alloc_hook. No other users for now.