From: Tejun Heo Date: Fri, 22 May 2026 17:06:01 +0000 (-1000) Subject: sched_ext: Sub-allocator over kernel-claimed BPF arena pages X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9eca087deb0b35f3170109a9630a6c5c06c2e222;p=thirdparty%2Fkernel%2Flinux.git sched_ext: Sub-allocator over kernel-claimed BPF arena pages Build a per-scheduler sub-allocator on top of pages claimed from the BPF arena registered in the previous patch. Subsequent kernel-managed arena-resident structures (e.g. per-CPU set_cmask cmask) carve their storage from this pool. scx_arena_pool_init() creates a gen_pool. scx_arena_alloc() returns the kernel VA. On exhaustion, the pool grows by claiming more pages via bpf_arena_alloc_pages_sleepable(). Chunks are added at the kernel-side mapping address. Callers translate to the BPF-arena form themselves if needed. Allocations sleep (GFP_KERNEL) - they may grow the pool through vzalloc and arena page allocation. All current consumers run from the enable path (after ops.init() and the kernel-side arena auto-discovery, before validate_ops()), where sleeping is fine. scx_arena_pool_destroy() walks each chunk, returns outstanding ranges to the gen_pool with gen_pool_free() and then calls gen_pool_destroy(). The underlying arena pages are released when the arena map itself is torn down, so the pool destroy doesn't free them explicitly. v2: Switch scx_arena_alloc() to a loop. (Andrea) Signed-off-by: Tejun Heo Reviewed-by: Andrea Righi --- diff --git a/kernel/sched/build_policy.c b/kernel/sched/build_policy.c index 5e76c9177d540..067979a7b69ec 100644 --- a/kernel/sched/build_policy.c +++ b/kernel/sched/build_policy.c @@ -59,12 +59,16 @@ #ifdef CONFIG_SCHED_CLASS_EXT # include +# include +# include # include "ext_types.h" # include "ext_internal.h" # include "ext_cid.h" +# include "ext_arena.h" # include "ext_idle.h" # include "ext.c" # include "ext_cid.c" +# include "ext_arena.c" # include "ext_idle.c" #endif diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index 53708fd3cc349..f5c67e3ff0753 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -5003,6 +5003,7 @@ static void scx_sched_free_rcu_work(struct work_struct *work) rhashtable_free_and_destroy(&sch->dsq_hash, NULL, NULL); free_exit_info(sch->exit_info); + scx_arena_pool_destroy(sch); if (sch->arena_map) bpf_map_put(sch->arena_map); kfree(sch); @@ -7155,6 +7156,12 @@ static void scx_root_enable_workfn(struct kthread_work *work) sch->exit_info->flags |= SCX_EFLAG_INITIALIZED; } + ret = scx_arena_pool_init(sch); + if (ret) { + cpus_read_unlock(); + goto err_disable; + } + for (i = SCX_OPI_CPU_HOTPLUG_BEGIN; i < SCX_OPI_CPU_HOTPLUG_END; i++) if (((void (**)(void))ops)[i]) set_bit(i, sch->has_op); @@ -7473,6 +7480,10 @@ static void scx_sub_enable_workfn(struct kthread_work *work) sch->exit_info->flags |= SCX_EFLAG_INITIALIZED; } + ret = scx_arena_pool_init(sch); + if (ret) + goto err_disable; + if (validate_ops(sch, ops)) goto err_disable; diff --git a/kernel/sched/ext_arena.c b/kernel/sched/ext_arena.c new file mode 100644 index 0000000000000..b413e155ba6b1 --- /dev/null +++ b/kernel/sched/ext_arena.c @@ -0,0 +1,126 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * BPF extensible scheduler class: Documentation/scheduler/sched-ext.rst + * + * scx_arena_pool: kernel-side sub-allocator over BPF-arena pages. + * + * Each chunk added to @sch->arena_pool comes from one + * bpf_arena_alloc_pages_sleepable() call and is registered at the + * kernel-side mapping address. Callers translate to the BPF-arena form + * themselves if needed. + * + * Allocations grow the pool on demand. Underlying arena pages are released + * when the arena map itself is torn down. + * + * Copyright (c) 2026 Meta Platforms, Inc. and affiliates. + * Copyright (c) 2026 Tejun Heo + */ + +enum scx_arena_consts { + SCX_ARENA_MIN_ORDER = 3, /* 8-byte minimum sub-allocation */ + SCX_ARENA_GROW_PAGES = 4, /* per growth */ +}; + +s32 scx_arena_pool_init(struct scx_sched *sch) +{ + if (!sch->arena_map) + return 0; + + sch->arena_pool = gen_pool_create(SCX_ARENA_MIN_ORDER, NUMA_NO_NODE); + if (!sch->arena_pool) + return -ENOMEM; + return 0; +} + +static void scx_arena_clear_chunk(struct gen_pool *pool, struct gen_pool_chunk *chunk, + void *data) +{ + int order = pool->min_alloc_order; + size_t chunk_sz = chunk->end_addr - chunk->start_addr + 1; + unsigned long end_bit = chunk_sz >> order; + unsigned long b, e; + + for_each_set_bitrange(b, e, chunk->bits, end_bit) + gen_pool_free(pool, chunk->start_addr + (b << order), + (e - b) << order); +} + +/* + * Tear down the pool. Outstanding gen_pool allocations are freed via + * scx_arena_clear_chunk() so gen_pool_destroy() doesn't BUG. The underlying + * arena pages are released when the arena map itself is torn down. + */ +void scx_arena_pool_destroy(struct scx_sched *sch) +{ + if (!sch->arena_pool) + return; + gen_pool_for_each_chunk(sch->arena_pool, scx_arena_clear_chunk, NULL); + gen_pool_destroy(sch->arena_pool); + sch->arena_pool = NULL; +} + +/* + * Grow the pool by @page_cnt pages. bpf_arena_alloc_pages_sleepable() and + * gen_pool_add() (which calls vzalloc(GFP_KERNEL)) require a sleepable + * context. + */ +static int scx_arena_grow(struct scx_sched *sch, u32 page_cnt) +{ + u64 kern_vm_start; + u32 uaddr32; + void *p; + int ret; + + if (!sch->arena_map || !sch->arena_pool) + return -EINVAL; + + p = bpf_arena_alloc_pages_sleepable(sch->arena_map, NULL, + page_cnt, NUMA_NO_NODE, 0); + if (!p) + return -ENOMEM; + + uaddr32 = (u32)(unsigned long)p; + kern_vm_start = bpf_arena_map_kern_vm_start(sch->arena_map); + + ret = gen_pool_add(sch->arena_pool, kern_vm_start + uaddr32, + page_cnt * PAGE_SIZE, NUMA_NO_NODE); + if (ret) { + bpf_arena_free_pages_non_sleepable(sch->arena_map, p, page_cnt); + return ret; + } + return 0; +} + +/* + * Allocate @size bytes from the arena pool. Returns kernel VA on success, NULL + * on failure. May grow the pool via scx_arena_grow() which sleeps. Caller must + * be in a GFP_KERNEL context. + */ +void *scx_arena_alloc(struct scx_sched *sch, size_t size) +{ + unsigned long kern_va; + u32 page_cnt; + + might_sleep(); + + if (!sch->arena_pool) + return NULL; + + while (true) { + kern_va = gen_pool_alloc(sch->arena_pool, size); + if (kern_va) + break; + page_cnt = max_t(u32, SCX_ARENA_GROW_PAGES, + (size + PAGE_SIZE - 1) >> PAGE_SHIFT); + if (scx_arena_grow(sch, page_cnt)) + return NULL; + } + + return (void *)kern_va; +} + +void scx_arena_free(struct scx_sched *sch, void *kern_va, size_t size) +{ + if (sch->arena_pool && kern_va) + gen_pool_free(sch->arena_pool, (unsigned long)kern_va, size); +} diff --git a/kernel/sched/ext_arena.h b/kernel/sched/ext_arena.h new file mode 100644 index 0000000000000..4f36101601024 --- /dev/null +++ b/kernel/sched/ext_arena.h @@ -0,0 +1,18 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * BPF extensible scheduler class: Documentation/scheduler/sched-ext.rst + * + * Copyright (c) 2025 Meta Platforms, Inc. and affiliates. + * Copyright (c) 2025 Tejun Heo + */ +#ifndef _KERNEL_SCHED_EXT_ARENA_H +#define _KERNEL_SCHED_EXT_ARENA_H + +struct scx_sched; + +s32 scx_arena_pool_init(struct scx_sched *sch); +void scx_arena_pool_destroy(struct scx_sched *sch); +void *scx_arena_alloc(struct scx_sched *sch, size_t size); +void scx_arena_free(struct scx_sched *sch, void *kern_va, size_t size); + +#endif /* _KERNEL_SCHED_EXT_ARENA_H */ diff --git a/kernel/sched/ext_internal.h b/kernel/sched/ext_internal.h index d40cfd29ddaa2..ff7e882bd67a8 100644 --- a/kernel/sched/ext_internal.h +++ b/kernel/sched/ext_internal.h @@ -1116,8 +1116,13 @@ struct scx_sched { * Arena map auto-discovered from member progs at struct_ops attach. * cid-form schedulers must use exactly one arena across all member * progs. NULL on cpu-form. + * + * @arena_pool sub-allocates @arena_map. Each gen_pool chunk is added + * at the kernel-side mapping address. Grows on demand and pages are + * not released until sched destroy. */ struct bpf_map *arena_map; + struct gen_pool *arena_pool; DECLARE_BITMAP(has_op, SCX_OPI_END);