Re: [PATCH v3 10/15] mm/slab: kmalloc: pass requests larger than order-1 page to page allocator

From: Vlastimil Babka
Date: Thu Jul 28 2022 - 12:25:46 EST

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On 7/12/22 15:39, Hyeonggon Yoo wrote:
> There is not much benefit for serving large objects in kmalloc().
> Let's pass large requests to page allocator like SLUB for better
> maintenance of common code.
>
> Signed-off-by: Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx>

Reviewed-by: Vlastimil Babka <vbabka@xxxxxxx>

> ---
> v2->v3:
> This patch is basically same but it now depends on
> kmalloc_large_node_notrace().
>
> include/linux/slab.h | 23 ++++-------------
> mm/slab.c | 60 +++++++++++++++++++++++++++++++-------------
> mm/slab.h | 3 +++
> mm/slab_common.c | 25 ++++++++++++------
> mm/slub.c | 19 --------------
> 5 files changed, 68 insertions(+), 62 deletions(-)
>
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index fd2e129fc813..4ee5b2fed164 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -243,27 +243,17 @@ static inline unsigned int arch_slab_minalign(void)
>
> #ifdef CONFIG_SLAB
> /*
> - * The largest kmalloc size supported by the SLAB allocators is
> - * 32 megabyte (2^25) or the maximum allocatable page order if that is
> - * less than 32 MB.
> - *
> - * WARNING: Its not easy to increase this value since the allocators have
> - * to do various tricks to work around compiler limitations in order to
> - * ensure proper constant folding.
> + * SLAB and SLUB directly allocates requests fitting in to an order-1 page
> + * (PAGE_SIZE*2). Larger requests are passed to the page allocator.
> */
> -#define KMALLOC_SHIFT_HIGH ((MAX_ORDER + PAGE_SHIFT - 1) <= 25 ? \
> - (MAX_ORDER + PAGE_SHIFT - 1) : 25)
> -#define KMALLOC_SHIFT_MAX KMALLOC_SHIFT_HIGH
> +#define KMALLOC_SHIFT_HIGH (PAGE_SHIFT + 1)
> +#define KMALLOC_SHIFT_MAX (MAX_ORDER + PAGE_SHIFT - 1)
> #ifndef KMALLOC_SHIFT_LOW
> #define KMALLOC_SHIFT_LOW 5
> #endif
> #endif
>
> #ifdef CONFIG_SLUB
> -/*
> - * SLUB directly allocates requests fitting in to an order-1 page
> - * (PAGE_SIZE*2). Larger requests are passed to the page allocator.
> - */
> #define KMALLOC_SHIFT_HIGH (PAGE_SHIFT + 1)
> #define KMALLOC_SHIFT_MAX (MAX_ORDER + PAGE_SHIFT - 1)
> #ifndef KMALLOC_SHIFT_LOW
> @@ -415,10 +405,6 @@ static __always_inline unsigned int __kmalloc_index(size_t size,
> if (size <= 512 * 1024) return 19;
> if (size <= 1024 * 1024) return 20;
> if (size <= 2 * 1024 * 1024) return 21;
> - if (size <= 4 * 1024 * 1024) return 22;
> - if (size <= 8 * 1024 * 1024) return 23;
> - if (size <= 16 * 1024 * 1024) return 24;
> - if (size <= 32 * 1024 * 1024) return 25;
>
> if (!IS_ENABLED(CONFIG_PROFILE_ALL_BRANCHES) && size_is_constant)
> BUILD_BUG_ON_MSG(1, "unexpected size in kmalloc_index()");
> @@ -428,6 +414,7 @@ static __always_inline unsigned int __kmalloc_index(size_t size,
> /* Will never be reached. Needed because the compiler may complain */
> return -1;
> }
> +static_assert(PAGE_SHIFT <= 20);
> #define kmalloc_index(s) __kmalloc_index(s, true)
> #endif /* !CONFIG_SLOB */
>
> diff --git a/mm/slab.c b/mm/slab.c
> index ab34727d61b2..a2f43425a0ae 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3585,11 +3585,19 @@ __do_kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller)
> struct kmem_cache *cachep;
> void *ret;
>
> - if (unlikely(size > KMALLOC_MAX_CACHE_SIZE))
> - return NULL;
> + if (unlikely(size > KMALLOC_MAX_CACHE_SIZE)) {
> + ret = kmalloc_large_node_notrace(size, flags, node);
> +
> + trace_kmalloc_node(caller, ret, NULL, size,
> + PAGE_SIZE << get_order(size),
> + flags, node);
> + return ret;
> + }
> +
> cachep = kmalloc_slab(size, flags);
> if (unlikely(ZERO_OR_NULL_PTR(cachep)))
> return cachep;
> +
> ret = kmem_cache_alloc_node_trace(cachep, flags, node, size);
> ret = kasan_kmalloc(cachep, ret, size, flags);
>
> @@ -3664,17 +3672,27 @@ EXPORT_SYMBOL(kmem_cache_free);
>
> void kmem_cache_free_bulk(struct kmem_cache *orig_s, size_t size, void **p)
> {
> - struct kmem_cache *s;
> - size_t i;
>
> local_irq_disable();
> - for (i = 0; i < size; i++) {
> + for (int i = 0; i < size; i++) {
> void *objp = p[i];
> + struct kmem_cache *s;
>
> - if (!orig_s) /* called via kfree_bulk */
> - s = virt_to_cache(objp);
> - else
> + if (!orig_s) {
> + struct folio *folio = virt_to_folio(objp);
> +
> + /* called via kfree_bulk */
> + if (!folio_test_slab(folio)) {
> + local_irq_enable();
> + free_large_kmalloc(folio, objp);
> + local_irq_disable();
> + continue;
> + }
> + s = folio_slab(folio)->slab_cache;
> + } else {
> s = cache_from_obj(orig_s, objp);
> + }
> +
> if (!s)
> continue;
>
> @@ -3703,20 +3721,24 @@ void kfree(const void *objp)
> {
> struct kmem_cache *c;
> unsigned long flags;
> + struct folio *folio;
>
> trace_kfree(_RET_IP_, objp);
>
> if (unlikely(ZERO_OR_NULL_PTR(objp)))
> return;
> - local_irq_save(flags);
> - kfree_debugcheck(objp);
> - c = virt_to_cache(objp);
> - if (!c) {
> - local_irq_restore(flags);
> +
> + folio = virt_to_folio(objp);
> + if (!folio_test_slab(folio)) {
> + free_large_kmalloc(folio, (void *)objp);
> return;
> }
> - debug_check_no_locks_freed(objp, c->object_size);
>
> + c = folio_slab(folio)->slab_cache;
> +
> + local_irq_save(flags);
> + kfree_debugcheck(objp);
> + debug_check_no_locks_freed(objp, c->object_size);
> debug_check_no_obj_freed(objp, c->object_size);
> __cache_free(c, (void *)objp, _RET_IP_);
> local_irq_restore(flags);
> @@ -4138,15 +4160,17 @@ void __check_heap_object(const void *ptr, unsigned long n,
> size_t __ksize(const void *objp)
> {
> struct kmem_cache *c;
> - size_t size;
> + struct folio *folio;
>
> BUG_ON(!objp);
> if (unlikely(objp == ZERO_SIZE_PTR))
> return 0;
>
> - c = virt_to_cache(objp);
> - size = c ? c->object_size : 0;
> + folio = virt_to_folio(objp);
> + if (!folio_test_slab(folio))
> + return folio_size(folio);
>
> - return size;
> + c = folio_slab(folio)->slab_cache;
> + return c->object_size;
> }
> EXPORT_SYMBOL(__ksize);
> diff --git a/mm/slab.h b/mm/slab.h
> index 7cb51ff44f0c..c81c92d421f1 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -669,6 +669,9 @@ static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x)
> print_tracking(cachep, x);
> return cachep;
> }
> +
> +void free_large_kmalloc(struct folio *folio, void *object);
> +
> #endif /* CONFIG_SLOB */
>
> static inline size_t slab_ksize(const struct kmem_cache *s)
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index 9c46e2f9589f..0dff46fb7193 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -771,8 +771,8 @@ struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags)
>
> /*
> * kmalloc_info[] is to make slub_debug=,kmalloc-xx option work at boot time.
> - * kmalloc_index() supports up to 2^25=32MB, so the final entry of the table is
> - * kmalloc-32M.
> + * kmalloc_index() supports up to 2^21=2MB, so the final entry of the table is
> + * kmalloc-2M.
> */
> const struct kmalloc_info_struct kmalloc_info[] __initconst = {
> INIT_KMALLOC_INFO(0, 0),
> @@ -796,11 +796,7 @@ const struct kmalloc_info_struct kmalloc_info[] __initconst = {
> INIT_KMALLOC_INFO(262144, 256k),
> INIT_KMALLOC_INFO(524288, 512k),
> INIT_KMALLOC_INFO(1048576, 1M),
> - INIT_KMALLOC_INFO(2097152, 2M),
> - INIT_KMALLOC_INFO(4194304, 4M),
> - INIT_KMALLOC_INFO(8388608, 8M),
> - INIT_KMALLOC_INFO(16777216, 16M),
> - INIT_KMALLOC_INFO(33554432, 32M)
> + INIT_KMALLOC_INFO(2097152, 2M)
> };
>
> /*
> @@ -913,6 +909,21 @@ void __init create_kmalloc_caches(slab_flags_t flags)
> /* Kmalloc array is now usable */
> slab_state = UP;
> }
> +
> +void free_large_kmalloc(struct folio *folio, void *object)
> +{
> + unsigned int order = folio_order(folio);
> +
> + if (WARN_ON_ONCE(order == 0))
> + pr_warn_once("object pointer: 0x%p\n", object);
> +
> + kmemleak_free(object);
> + kasan_kfree_large(object);
> +
> + mod_lruvec_page_state(folio_page(folio, 0), NR_SLAB_UNRECLAIMABLE_B,
> + -(PAGE_SIZE << order));
> + __free_pages(folio_page(folio, 0), order);
> +}
> #endif /* !CONFIG_SLOB */
>
> gfp_t kmalloc_fix_flags(gfp_t flags)
> diff --git a/mm/slub.c b/mm/slub.c
> index 3d02cf44adf7..6cb7ca27f3b7 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1704,12 +1704,6 @@ static bool freelist_corrupted(struct kmem_cache *s, struct slab *slab,
> * Hooks for other subsystems that check memory allocations. In a typical
> * production configuration these hooks all should produce no code at all.
> */
> -static __always_inline void kfree_hook(void *x)
> -{
> - kmemleak_free(x);
> - kasan_kfree_large(x);
> -}
> -
> static __always_inline bool slab_free_hook(struct kmem_cache *s,
> void *x, bool init)
> {
> @@ -3550,19 +3544,6 @@ struct detached_freelist {
> struct kmem_cache *s;
> };
>
> -static inline void free_large_kmalloc(struct folio *folio, void *object)
> -{
> - unsigned int order = folio_order(folio);
> -
> - if (WARN_ON_ONCE(order == 0))
> - pr_warn_once("object pointer: 0x%p\n", object);
> -
> - kfree_hook(object);
> - mod_lruvec_page_state(folio_page(folio, 0), NR_SLAB_UNRECLAIMABLE_B,
> - -(PAGE_SIZE << order));
> - __free_pages(folio_page(folio, 0), order);
> -}
> -
> /*
> * This function progressively scans the array with free objects (with
> * a limited look ahead) and extract objects belonging to the same

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