On Thu, May 18, 2023 at 9:58 AM Kent Overstreet
<kent.overstreet@xxxxxxxxx> wrote:
>
> On Thu, May 18, 2023 at 09:33:20AM -0700, Song Liu wrote:
> > I am working on patches based on the discussion in [1]. I am planning to
> > send v1 for review in a week or so.
>
> For reference, here's my own (early, but functioning :) slab allocator:
>
> Look forward to comparing!
This looks similar to the bpf_prog_pack allocator we use for BPF at the
moment. (search for bpf_prog_pack in kernel/bpf/core.c). I guess we
can also use bpf_prog_pack for bcachefs for now.
Thanks,
Song
> -->--
> From 6eeb6b8ef4271ea1a8d9cac7fbaeeb7704951976 Mon Sep 17 00:00:00 2001
> From: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> Date: Wed, 17 May 2023 01:22:06 -0400
> Subject: [PATCH] mm: jit/text allocator
>
> This provides a new, very simple slab allocator for jit/text, i.e. bpf,
> ftrace trampolines, or bcachefs unpack functions.
>
> With this API we can avoid ever mapping pages both writeable and
> executable (not implemented in this patch: need to tweak
> module_alloc()), and it also supports sub-page sized allocations.
>
> Signed-off-by: Kent Overstreet <kent.overstreet@xxxxxxxxx>
>
> diff --git a/include/linux/jitalloc.h b/include/linux/jitalloc.h
> new file mode 100644
> index 0000000000..f1549d60e8
> --- /dev/null
> +++ b/include/linux/jitalloc.h
> @@ -0,0 +1,9 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef _LINUX_JITALLOC_H
> +#define _LINUX_JITALLOC_H
> +
> +void jit_update(void *buf, void *new_buf, size_t len);
> +void jit_free(void *buf);
> +void *jit_alloc(void *buf, size_t len);
> +
> +#endif /* _LINUX_JITALLOC_H */
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 4751031f3f..ff26a4f0c9 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1202,6 +1202,9 @@ config LRU_GEN_STATS
> This option has a per-memcg and per-node memory overhead.
> # }
>
> +config JITALLOC
> + bool
> +
> source "mm/damon/Kconfig"
>
> endmenu
> diff --git a/mm/Makefile b/mm/Makefile
> index c03e1e5859..25e82db9e8 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -138,3 +138,4 @@ obj-$(CONFIG_IO_MAPPING) += io-mapping.o
> obj-$(CONFIG_HAVE_BOOTMEM_INFO_NODE) += bootmem_info.o
> obj-$(CONFIG_GENERIC_IOREMAP) += ioremap.o
> obj-$(CONFIG_SHRINKER_DEBUG) += shrinker_debug.o
> +obj-$(CONFIG_JITALLOC) += jitalloc.o
> diff --git a/mm/jitalloc.c b/mm/jitalloc.c
> new file mode 100644
> index 0000000000..7c4d621802
> --- /dev/null
> +++ b/mm/jitalloc.c
> @@ -0,0 +1,187 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/gfp.h>
> +#include <linux/highmem.h>
> +#include <linux/jitalloc.h>
> +#include <linux/mm.h>
> +#include <linux/moduleloader.h>
> +#include <linux/mutex.h>
> +#include <linux/set_memory.h>
> +#include <linux/vmalloc.h>
> +
> +#include <asm/text-patching.h>
> +
> +static DEFINE_MUTEX(jit_alloc_lock);
> +
> +struct jit_cache {
> + unsigned obj_size_bits;
> + unsigned objs_per_slab;
> + struct list_head partial;
> +};
> +
> +#define JITALLOC_MIN_SIZE 16
> +#define NR_JIT_CACHES ilog2(PAGE_SIZE / JITALLOC_MIN_SIZE)
> +
> +static struct jit_cache jit_caches[NR_JIT_CACHES];
> +
> +struct jit_slab {
> + unsigned long __page_flags;
> +
> + struct jit_cache *cache;
> + void *executably_mapped;;
> + unsigned long *objs_allocated; /* bitmap of free objects */
> + struct list_head list;
> +};
> +
> +#define folio_jit_slab(folio) (_Generic((folio), \
> + const struct folio *: (const struct jit_slab *)(folio), \
> + struct folio *: (struct jit_slab *)(folio)))
> +
> +#define jit_slab_folio(s) (_Generic((s), \
> + const struct jit_slab *: (const struct folio *)s, \
> + struct jit_slab *: (struct folio *)s))
> +
> +static struct jit_slab *jit_slab_alloc(struct jit_cache *cache)
> +{
> + void *executably_mapped = module_alloc(PAGE_SIZE);
> + struct page *page;
> + struct folio *folio;
> + struct jit_slab *slab;
> + unsigned long *objs_allocated;
> +
> + if (!executably_mapped)
> + return NULL;
> +
> + objs_allocated = kcalloc(BITS_TO_LONGS(cache->objs_per_slab), sizeof(unsigned long), GFP_KERNEL);
> + if (!objs_allocated ) {
> + vfree(executably_mapped);
> + return NULL;
> + }
> +
> + set_vm_flush_reset_perms(executably_mapped);
> + set_memory_rox((unsigned long) executably_mapped, 1);
> +
> + page = vmalloc_to_page(executably_mapped);
> + folio = page_folio(page);
> +
> + __folio_set_slab(folio);
> + slab = folio_jit_slab(folio);
> + slab->cache = cache;
> + slab->executably_mapped = executably_mapped;
> + slab->objs_allocated = objs_allocated;
> + INIT_LIST_HEAD(&slab->list);
> +
> + return slab;
> +}
> +
> +static void *jit_cache_alloc(void *buf, size_t len, struct jit_cache *cache)
> +{
> + struct jit_slab *s =
> + list_first_entry_or_null(&cache->partial, struct jit_slab, list) ?:
> + jit_slab_alloc(cache);
> + unsigned obj_idx, nr_allocated;
> +
> + if (!s)
> + return NULL;
> +
> + obj_idx = find_first_zero_bit(s->objs_allocated, cache->objs_per_slab);
> +
> + BUG_ON(obj_idx >= cache->objs_per_slab);
> + __set_bit(obj_idx, s->objs_allocated);
> +
> + nr_allocated = bitmap_weight(s->objs_allocated, s->cache->objs_per_slab);
> +
> + if (nr_allocated == s->cache->objs_per_slab) {
> + list_del_init(&s->list);
> + } else if (nr_allocated == 1) {
> + list_del(&s->list);
> + list_add(&s->list, &s->cache->partial);
> + }
> +
> + return s->executably_mapped + (obj_idx << cache->obj_size_bits);
> +}
> +
> +void jit_update(void *buf, void *new_buf, size_t len)
> +{
> + text_poke_copy(buf, new_buf, len);
> +}
> +EXPORT_SYMBOL_GPL(jit_update);
> +
> +void jit_free(void *buf)
> +{
> + struct page *page;
> + struct folio *folio;
> + struct jit_slab *s;
> + unsigned obj_idx, nr_allocated;
> + size_t offset;
> +
> + if (!buf)
> + return;
> +
> + page = vmalloc_to_page(buf);
> + folio = page_folio(page);
> + offset = offset_in_folio(folio, buf);
> +
> + if (!folio_test_slab(folio)) {
> + vfree(buf);
> + return;
> + }
> +
> + s = folio_jit_slab(folio);
> +
> + mutex_lock(&jit_alloc_lock);
> + obj_idx = offset >> s->cache->obj_size_bits;
> +
> + __clear_bit(obj_idx, s->objs_allocated);
> +
> + nr_allocated = bitmap_weight(s->objs_allocated, s->cache->objs_per_slab);
> +
> + if (nr_allocated == 0) {
> + list_del(&s->list);
> + kfree(s->objs_allocated);
> + folio_put(folio);
> + } else if (nr_allocated + 1 == s->cache->objs_per_slab) {
> + list_del(&s->list);
> + list_add(&s->list, &s->cache->partial);
> + }
> +
> + mutex_unlock(&jit_alloc_lock);
> +}
> +EXPORT_SYMBOL_GPL(jit_free);
> +
> +void *jit_alloc(void *buf, size_t len)
> +{
> + unsigned jit_cache_idx = ilog2(roundup_pow_of_two(len) / 16);
> + void *p;
> +
> + if (jit_cache_idx < NR_JIT_CACHES) {
> + mutex_lock(&jit_alloc_lock);
> + p = jit_cache_alloc(buf, len, &jit_caches[jit_cache_idx]);
> + mutex_unlock(&jit_alloc_lock);
> + } else {
> + p = module_alloc(len);
> + if (p) {
> + set_vm_flush_reset_perms(p);
> + set_memory_rox((unsigned long) p, DIV_ROUND_UP(len, PAGE_SIZE));
> + }
> + }
> +
> + if (p && buf)
> + jit_update(p, buf, len);
> +
> + return p;
> +}
> +EXPORT_SYMBOL_GPL(jit_alloc);
> +
> +static int __init jit_alloc_init(void)
> +{
> + for (unsigned i = 0; i < ARRAY_SIZE(jit_caches); i++) {
> + jit_caches[i].obj_size_bits = ilog2(JITALLOC_MIN_SIZE) + i;
> + jit_caches[i].objs_per_slab = PAGE_SIZE >> jit_caches[i].obj_size_bits;
> +
> + INIT_LIST_HEAD(&jit_caches[i].partial);
> + }
> +
> + return 0;
> +}
> +core_initcall(jit_alloc_init);
>
