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aligned to it, each object ends up with some unused space because of alignment. If this wasted space is big enough, we can use it to store the slabobj_ext metadata instead of wasting it. On my system, this happens with caches like kmem_cache, mm_struct, pid, task_struct, sighand_cache, xfs_inode, and others. To place the slabobj_ext metadata within each object, the existing slab_obj_ext() logic can still be used by setting: - slab->obj_exts = slab_address(slab) + s->red_left_zone + (slabobj_ext offset) - stride = s->size slab_obj_ext() doesn't need know where the metadata is stored, so this method works without adding extra overhead to slab_obj_ext(). A good example benefiting from this optimization is xfs_inode (object_size: 992, align: 64). To measure memory savings, 2 millions of files were created on XFS. [ MEMCG=y, MEM_ALLOC_PROFILING=n ] Before patch (creating 2M directories on xfs): Slab: 6693844 kB SReclaimable: 6016332 kB SUnreclaim: 677512 kB After patch (creating 2M directories on xfs): Slab: 6697572 kB SReclaimable: 6034744 kB SUnreclaim: 662828 kB (-14.3 MiB) Enjoy the memory savings! Suggested-by: Vlastimil Babka Signed-off-by: Harry Yoo --- include/linux/slab.h | 9 ++++++ mm/slab_common.c | 6 ++-- mm/slub.c | 72 ++++++++++++++++++++++++++++++++++++++++++-- 3 files changed, 82 insertions(+), 5 deletions(-) diff --git a/include/linux/slab.h b/include/linux/slab.h index 561597dd2164..fd09674cc117 100644 --- a/include/linux/slab.h +++ b/include/linux/slab.h @@ -59,6 +59,9 @@ enum _slab_flag_bits { _SLAB_CMPXCHG_DOUBLE, #ifdef CONFIG_SLAB_OBJ_EXT _SLAB_NO_OBJ_EXT, +#endif +#if defined(CONFIG_SLAB_OBJ_EXT) && defined(CONFIG_64BIT) + _SLAB_OBJ_EXT_IN_OBJ, #endif _SLAB_FLAGS_LAST_BIT }; @@ -244,6 +247,12 @@ enum _slab_flag_bits { #define SLAB_NO_OBJ_EXT __SLAB_FLAG_UNUSED #endif +#if defined(CONFIG_SLAB_OBJ_EXT) && defined(CONFIG_64BIT) +#define SLAB_OBJ_EXT_IN_OBJ __SLAB_FLAG_BIT(_SLAB_OBJ_EXT_IN_OBJ) +#else +#define SLAB_OBJ_EXT_IN_OBJ __SLAB_FLAG_UNUSED +#endif + /* * ZERO_SIZE_PTR will be returned for zero sized kmalloc requests. * diff --git a/mm/slab_common.c b/mm/slab_common.c index 2c2ed2452271..bfe2f498e622 100644 --- a/mm/slab_common.c +++ b/mm/slab_common.c @@ -43,11 +43,13 @@ DEFINE_MUTEX(slab_mutex); struct kmem_cache *kmem_cache; /* - * Set of flags that will prevent slab merging + * Set of flags that will prevent slab merging. + * Any flag that adds per-object metadata should be included, + * since slab merging can update s->inuse that affects the metadata layout. */ #define SLAB_NEVER_MERGE (SLAB_RED_ZONE | SLAB_POISON | SLAB_STORE_USER | \ SLAB_TRACE | SLAB_TYPESAFE_BY_RCU | SLAB_NOLEAKTRACE | \ - SLAB_FAILSLAB | SLAB_NO_MERGE) + SLAB_FAILSLAB | SLAB_NO_MERGE | SLAB_OBJ_EXT_IN_OBJ) #define SLAB_MERGE_SAME (SLAB_RECLAIM_ACCOUNT | SLAB_CACHE_DMA | \ SLAB_CACHE_DMA32 | SLAB_ACCOUNT) diff --git a/mm/slub.c b/mm/slub.c index 8101df5fdccf..7de6e8f8f8c2 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -970,6 +970,40 @@ static inline bool obj_exts_in_slab(struct kmem_cache *s, struct slab *slab) { return false; } + +#endif + +#if defined(CONFIG_SLAB_OBJ_EXT) && defined(CONFIG_64BIT) +static bool obj_exts_in_object(struct kmem_cache *s) +{ + return s->flags & SLAB_OBJ_EXT_IN_OBJ; +} + +static unsigned int obj_exts_offset_in_object(struct kmem_cache *s) +{ + unsigned int offset = get_info_end(s); + + if (kmem_cache_debug_flags(s, SLAB_STORE_USER)) + offset += sizeof(struct track) * 2; + + if (slub_debug_orig_size(s)) + offset += ALIGN(sizeof(unsigned int), + __alignof__(unsigned long)); + + offset += kasan_metadata_size(s, false); + + return offset; +} +#else +static inline bool obj_exts_in_object(struct kmem_cache *s) +{ + return false; +} + +static inline unsigned int obj_exts_offset_in_object(struct kmem_cache *s) +{ + return 0; +} #endif #ifdef CONFIG_SLUB_DEBUG @@ -1270,6 +1304,9 @@ static void print_trailer(struct kmem_cache *s, struct slab *slab, u8 *p) off += kasan_metadata_size(s, false); + if (obj_exts_in_object(s)) + off += sizeof(struct slabobj_ext); + if (off != size_from_object(s)) /* Beginning of the filler is the free pointer */ print_section(KERN_ERR, "Padding ", p + off, @@ -1439,7 +1476,10 @@ check_bytes_and_report(struct kmem_cache *s, struct slab *slab, * A. Free pointer (if we cannot overwrite object on free) * B. Tracking data for SLAB_STORE_USER * C. Original request size for kmalloc object (SLAB_STORE_USER enabled) - * D. Padding to reach required alignment boundary or at minimum + * D. KASAN alloc metadata (KASAN enabled) + * E. struct slabobj_ext to store accounting metadata + * (SLAB_OBJ_EXT_IN_OBJ enabled) + * F. Padding to reach required alignment boundary or at minimum * one word if debugging is on to be able to detect writes * before the word boundary. * @@ -1468,6 +1508,9 @@ static int check_pad_bytes(struct kmem_cache *s, struct slab *slab, u8 *p) off += kasan_metadata_size(s, false); + if (obj_exts_in_object(s)) + off += sizeof(struct slabobj_ext); + if (size_from_object(s) == off) return 1; @@ -2250,7 +2293,8 @@ static inline void free_slab_obj_exts(struct slab *slab) if (!obj_exts) return; - if (obj_exts_in_slab(slab->slab_cache, slab)) { + if (obj_exts_in_slab(slab->slab_cache, slab) || + obj_exts_in_object(slab->slab_cache)) { slab->obj_exts = 0; return; } @@ -2291,6 +2335,21 @@ static void alloc_slab_obj_exts_early(struct kmem_cache *s, struct slab *slab) if (IS_ENABLED(CONFIG_MEMCG)) slab->obj_exts |= MEMCG_DATA_OBJEXTS; slab_set_stride(slab, sizeof(struct slabobj_ext)); + } else if (obj_exts_in_object(s)) { + unsigned int offset = obj_exts_offset_in_object(s); + + slab->obj_exts = (unsigned long)slab_address(slab); + slab->obj_exts += s->red_left_pad; + slab->obj_exts += obj_exts_offset_in_object(s); + if (IS_ENABLED(CONFIG_MEMCG)) + slab->obj_exts |= MEMCG_DATA_OBJEXTS; + slab_set_stride(slab, s->size); + + for_each_object(addr, s, slab_address(slab), slab->objects) { + kasan_unpoison_range(addr + offset, + sizeof(struct slabobj_ext)); + memset(addr + offset, 0, sizeof(struct slabobj_ext)); + } } metadata_access_disable(); } @@ -7883,6 +7942,7 @@ static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s) { slab_flags_t flags = s->flags; unsigned int size = s->object_size; + unsigned int aligned_size; unsigned int order; /* @@ -7997,7 +8057,13 @@ static int calculate_sizes(struct kmem_cache_args *args, struct kmem_cache *s) * offset 0. In order to align the objects we have to simply size * each object to conform to the alignment. */ - size = ALIGN(size, s->align); + aligned_size = ALIGN(size, s->align); +#if defined(CONFIG_SLAB_OBJ_EXT) && defined(CONFIG_64BIT) + if (aligned_size - size >= sizeof(struct slabobj_ext)) + s->flags |= SLAB_OBJ_EXT_IN_OBJ; +#endif + size = aligned_size; + s->size = size; s->reciprocal_size = reciprocal_value(size); order = calculate_order(size); -- 2.43.0