On 3/4/22 07:34, 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>
Looks like it's on the right path! Some suggestions follow.
> ---
> include/linux/slab.h | 35 ++++++++++++++++-------------------
> mm/slab.c | 31 +++++++++++++++++++++++++++----
> mm/slab.h | 19 +++++++++++++++++++
> mm/slub.c | 19 -------------------
> 4 files changed, 62 insertions(+), 42 deletions(-)
>
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index 37bde99b74af..e7b3330db4f3 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -224,29 +224,19 @@ void kmem_dump_obj(void *object);
> * Kmalloc array related definitions
> */
>
> -#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
> +#ifdef CONFIG_SLAB
> +#define KMALLOC_SHIFT_HIGH (PAGE_SHIFT + 1)
> +#define KMALLOC_SHIFT_MAX (MAX_ORDER + PAGE_SHIFT - 1)
I think we should be able to also remove the larger sizes from
__kmalloc_index() later in this file.
> #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
> @@ -564,15 +554,15 @@ static __always_inline __alloc_size(1) void *kmalloc_large(size_t size, gfp_t fl
> * Try really hard to succeed the allocation but fail
> * eventually.
> */
> +#ifndef CONFIG_SLOB
> static __always_inline __alloc_size(1) void *kmalloc(size_t size, gfp_t flags)
> {
> if (__builtin_constant_p(size)) {
> -#ifndef CONFIG_SLOB
> unsigned int index;
> -#endif
> +
> if (size > KMALLOC_MAX_CACHE_SIZE)
> return kmalloc_large(size, flags);
> -#ifndef CONFIG_SLOB
> +
> index = kmalloc_index(size);
>
> if (!index)
> @@ -581,10 +571,17 @@ static __always_inline __alloc_size(1) void *kmalloc(size_t size, gfp_t flags)
> return kmem_cache_alloc_trace(
> kmalloc_caches[kmalloc_type(flags)][index],
> flags, size);
> -#endif
> }
> return __kmalloc(size, flags);
> }
> +#else
> +static __always_inline __alloc_size(1) void *kmalloc(size_t size, gfp_t flags)
> +{
> + if (__builtin_constant_p(size) && size > KMALLOC_MAX_CACHE_SIZE)
> + return kmalloc_large(size, flags);
> + return __kmalloc(size, flags);
> +}
> +#endif
>
> static __always_inline __alloc_size(1) void *kmalloc_node(size_t size, gfp_t flags, int node)
> {
> diff --git a/mm/slab.c b/mm/slab.c
> index ddf5737c63d9..570af6dc3478 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3624,7 +3624,8 @@ __do_kmalloc_node(size_t size, gfp_t flags, int node, unsigned long caller)
> void *ret;
>
> if (unlikely(size > KMALLOC_MAX_CACHE_SIZE))
> - return NULL;
> + return kmalloc_large(size, flags);
This loses the node information and NUMA locality. It would be better to
generalize kmalloc_large_node() from mm/slub.c instead.
> +
> cachep = kmalloc_slab(size, flags);
> if (unlikely(ZERO_OR_NULL_PTR(cachep)))
> return cachep;
> @@ -3685,7 +3686,8 @@ static __always_inline void *__do_kmalloc(size_t size, gfp_t flags,
> void *ret;
>
> if (unlikely(size > KMALLOC_MAX_CACHE_SIZE))
> - return NULL;
> + return kmalloc_large(size, flags);
> +
> cachep = kmalloc_slab(size, flags);
> if (unlikely(ZERO_OR_NULL_PTR(cachep)))
> return cachep;
> @@ -3739,14 +3741,21 @@ void kmem_cache_free_bulk(struct kmem_cache *orig_s, size_t size, void **p)
> {
> struct kmem_cache *s;
> size_t i;
> + struct folio *folio;
>
> local_irq_disable();
> for (i = 0; i < size; i++) {
> void *objp = p[i];
>
> - if (!orig_s) /* called via kfree_bulk */
> + if (!orig_s) {
> + /* called via kfree_bulk */
> + folio = virt_to_folio(objp);
> + if (unlikely(!folio_test_slab(folio))) {
> + free_large_kmalloc(folio, objp);
Hmm I'm not sure it's a good idea to call this and the page allocator with
disabled irq's. Maybe simply re-enable around it?
> + continue;
> + }
> s = virt_to_cache(objp);
Since we already have the folio, we shoold instead use folio_slab and
slab->slab_cache (see how mm/slub.c does it).
The same applies to functions below as well.
> - else
> + } else
> s = cache_from_obj(orig_s, objp);
> if (!s)
> continue;
> @@ -3776,11 +3785,20 @@ void kfree(const void *objp)
> {
> struct kmem_cache *c;
> unsigned long flags;
> + struct folio *folio;
> + void *object = (void *) objp;
>
> trace_kfree(_RET_IP_, objp);
>
> if (unlikely(ZERO_OR_NULL_PTR(objp)))
> return;
> +
> + folio = virt_to_folio(objp);
> + if (unlikely(!folio_test_slab(folio))) {
> + free_large_kmalloc(folio, object);
> + return;
> + }
> +
> local_irq_save(flags);
> kfree_debugcheck(objp);
> c = virt_to_cache(objp);
> @@ -4211,12 +4229,17 @@ void __check_heap_object(const void *ptr, unsigned long n,
> size_t __ksize(const void *objp)
> {
> struct kmem_cache *c;
> + struct folio *folio;
> size_t size;
>
> BUG_ON(!objp);
> if (unlikely(objp == ZERO_SIZE_PTR))
> return 0;
>
> + folio = virt_to_folio(objp);
> + if (!folio_test_slab(folio))
> + return folio_size(folio);
> +
> c = virt_to_cache(objp);
> size = c ? c->object_size : 0;
>
> diff --git a/mm/slab.h b/mm/slab.h
> index c7f2abc2b154..31e98beb47a3 100644
> --- a/mm/slab.h
> +++ b/mm/slab.h
> @@ -664,6 +664,25 @@ static inline struct kmem_cache *cache_from_obj(struct kmem_cache *s, void *x)
> print_tracking(cachep, x);
> return cachep;
> }
> +
> +static __always_inline void kfree_hook(void *x)
> +{
> + kmemleak_free(x);
> + kasan_kfree_large(x);
Looks like there's only one caller of kfree_hook() so we could do that
directly there.
> +}
> +
> +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);
> +}
> #endif /* CONFIG_SLOB */
>
> static inline size_t slab_ksize(const struct kmem_cache *s)
> diff --git a/mm/slub.c b/mm/slub.c
> index 261474092e43..04fd084f4709 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -1686,12 +1686,6 @@ static inline void *kmalloc_large_node_hook(void *ptr, size_t size, gfp_t flags)
> return ptr;
> }
>
> -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)
> {
> @@ -3535,19 +3529,6 @@ 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
