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Message-ID: <9b808582-3a64-b626-14a4-55e7d9040261@suse.cz>
Date: Thu, 24 Mar 2022 19:08:27 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Hyeonggon Yoo <42.hyeyoo@...il.com>, linux-mm@...ck.org
Cc: Christoph Lameter <cl@...ux.com>,
Pekka Enberg <penberg@...nel.org>,
David Rientjes <rientjes@...gle.com>,
Joonsoo Kim <iamjoonsoo.kim@....com>,
Andrew Morton <akpm@...ux-foundation.org>,
Marco Elver <elver@...gle.com>,
Matthew WilCox <willy@...radead.org>,
Roman Gushchin <roman.gushchin@...ux.dev>,
linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v1 09/15] mm/slab: kmalloc: pass requests larger than
order-1 page to page allocator
On 3/8/22 12:41, 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.
>
> [ vbabka@...e.cz: Enable and disable irq around free_large_kmalloc().
> Do not lose NUMA locality in __do_kmalloc_node().
> Use folio_slab(folio)->slab_cache instead of virt_to_cache().
> Remove large sizes in __kmalloc_index(). ]
Thanks for the mention but that's generally only done like this if I took
your patch and made those changes myself. But I just suggested them. Small
suggested changes like this are usually just mentioned in e.g. v1->v2
changelogs.
> Signed-off-by: Hyeonggon Yoo <42.hyeyoo@...il.com>
> ---
> include/linux/slab.h | 23 +++++-----------------
> mm/slab.c | 45 ++++++++++++++++++++++++++++++--------------
> mm/slab.h | 3 +++
> mm/slab_common.c | 25 +++++++++++++++++-------
> mm/slub.c | 19 -------------------
> 5 files changed, 57 insertions(+), 58 deletions(-)
>
> diff --git a/include/linux/slab.h b/include/linux/slab.h
> index dfcc8301d969..9ced225a3ea3 100644
> --- a/include/linux/slab.h
> +++ b/include/linux/slab.h
> @@ -226,27 +226,17 @@ void kmem_dump_obj(void *object);
>
> #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
> @@ -398,10 +388,6 @@ 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()");
> @@ -411,6 +397,7 @@ 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 6ebf509bf2de..f0041f0125ba 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3568,7 +3568,7 @@ __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_node(size, flags, node);
Similar issue with caller not traced.
> cachep = kmalloc_slab(size, flags);
> if (unlikely(ZERO_OR_NULL_PTR(cachep)))
> return cachep;
> @@ -3642,15 +3642,25 @@ 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 */
> - s = virt_to_cache(objp);
> - else
> + if (!orig_s) {
> + 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;
>
> @@ -3679,20 +3689,25 @@ void kfree(const void *objp)
> {
> struct kmem_cache *c;
> unsigned long flags;
> + struct folio *folio;
> + void *x = (void *) objp;
I think you don't need to add 'x', just do the cast while calling
free_large_kmalloc(), same as done for __cache_free().
>
> 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, x);
> 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);
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