On 7/10/24 7:43 AM, alexs@xxxxxxxxxx wrote:
> From: "Alex Shi (Tencent)" <alexs@xxxxxxxxxx>
>
> commit 21c690a349ba ("mm: introduce slabobj_ext to support slab object
> extensions") changed the folio/page->memcg_data define condition from
> MEMCG to SLAB_OBJ_EXT. And selected SLAB_OBJ_EXT for MEMCG, just for
> SLAB_MATCH(memcg_data, obj_exts), even no other relationship between them.
>
> Above action make memcg_data exposed and include SLAB_OBJ_EXT for
> !MEMCG. That's incorrect in logcial and pay on code size.
>
> As Vlastimil Babka suggested, let's add _unused_slab_obj_ext for
> SLAB_MATCH for slab.obj_exts while !MEMCG. That could resolve the match
> issue, clean up the feature logical. And decouple the SLAB_OBJ_EXT from
> MEMCG in next patch.
>
> Signed-off-by: Alex Shi (Tencent) <alexs@xxxxxxxxxx>
> Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Cc: Yoann Congal <yoann.congal@xxxxxxxx>
> Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> Cc: Petr Mladek <pmladek@xxxxxxxx>
> Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Cc: Vlastimil Babka <vbabka@xxxxxxx>
> ---
> v1->v3: take Vlastimil's suggestion and move SLAB_OBJ_EXT/MEMCG decouple
> to 2nd patch.
> ---
> include/linux/mm_types.h | 8 ++++++--
> mm/slab.h | 4 ++++
> 2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
> index ef09c4eef6d3..4ac3abc673d3 100644
> --- a/include/linux/mm_types.h
> +++ b/include/linux/mm_types.h
> @@ -180,8 +180,10 @@ struct page {
> /* Usage count. *DO NOT USE DIRECTLY*. See page_ref.h */
> atomic_t _refcount;
>
> -#ifdef CONFIG_SLAB_OBJ_EXT
> +#ifdef CONFIG_MEMCG
> unsigned long memcg_data;
> +#elif defined(CONFIG_SLAB_OBJ_EXT)
> + unsigned long _unused_slab_obj_ext;
> #endif
>
> /*
> @@ -343,8 +345,10 @@ struct folio {
> };
> atomic_t _mapcount;
> atomic_t _refcount;
> -#ifdef CONFIG_SLAB_OBJ_EXT
> +#ifdef CONFIG_MEMCG
> unsigned long memcg_data;
> +#elif defined(CONFIG_SLAB_OBJ_EXT)
> + unsigned long _unused_slab_obj_ext;
> #endif
> #if defined(WANT_PAGE_VIRTUAL)
> void *virtual;
> diff --git a/mm/slab.h b/mm/slab.h
> index 3586e6183224..8ffdd4f315f8 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -98,7 +98,11 @@ SLAB_MATCH(flags, __page_flags);
> SLAB_MATCH(compound_head, slab_cache); /* Ensure bit 0 is clear */
> SLAB_MATCH(_refcount, __page_refcount);
> #ifdef CONFIG_SLAB_OBJ_EXT
> +#ifdef CONFIG_MEMCG
> SLAB_MATCH(memcg_data, obj_exts);
> +#else
> +SLAB_MATCH(_unused_slab_obj_ext, obj_exts);
> +#endif
> #endif
Why not also #ifdef / #elif like above, instead of this nesting?
> #undef SLAB_MATCH
> static_assert(sizeof(struct slab) <= sizeof(struct page));
