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

On Fri, Feb 16, 2024 at 7:36 AM Vlastimil Babka [off-list ref] wrote:

On 2/12/24 22:39, Suren Baghdasaryan wrote:

quoted

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.

Yes, slabobj_ext overhead is much smaller than page_ext one but still
considerable and it would be harder to eliminate. Boot-time resizing
of the extension object might be doable but that again would be quite
complex and better be done as a separate patchset. This is lower on my
TODO list than page_ext ones since the overhead is order of magnitude
smaller.

quoted

 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.