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b=XB7ViVbI6QwMQAtAil6w+oL8bl0oAUYhmJxQH/p3CVU4rkIrtPxkP4wZHqFThxJaT Quip1QtcqkbzJwbhSLN2qv+Pdjk/CoYJIeYGN5ZR0ycpdWVXnz4d/pduzbZivrz1LZ 4KQ2rTsPHaiUf2AQEF5jpsTgRVvJzZT3rGU9Y/0139arL3KUA2HtyxlJXnTN/JcyW2 zP4cHBDOsfy/v3064tbJ//EMDQgf4qI7wL6986AU/Kes8ibuahwkM6z832ag2zcnIA JPyOoN1f623cxD12L7EzFewa2TcKySgmGyluNRSTYn84Y6FIQpfoBTPWZON07m542j fmEfYTtQcjX+g== From: Tejun Heo To: David Vernet , Andrea Righi , Changwoo Min , Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau , Kumar Kartikeya Dwivedi Cc: Peter Zijlstra , Catalin Marinas , Will Deacon , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , Andrew Morton , David Hildenbrand , Mike Rapoport , Emil Tsalapatis , sched-ext@lists.linux.dev, bpf@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Tejun Heo Subject: [PATCH 7/8] sched_ext: Sub-allocator over kernel-claimed BPF arena pages Date: Wed, 20 May 2026 13:50:51 -1000 Message-ID: <20260520235052.4180316-8-tj@kernel.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260520235052.4180316-1-tj@kernel.org> References: <20260520235052.4180316-1-tj@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Queue-Id: D755C180004 X-Rspamd-Server: rspam04 X-Stat-Signature: 5zduw6n46yuqycqrsza46xtiq3ok19cg X-HE-Tag: 1779321060-173598 X-HE-Meta: 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 nVrQpKGa wKFH0c9IX6ppIxR9vPbjNk91+dqTedP/+ZpoN9u/X2RIhKMJtEprAEL2GO0jPfCycmpPWWhw/1v6s9rbJdHDeqjK9zI8kqn4MzJmxNwnInhxhe8fLzeIybiaWaUdQkZVyFPmZ3oiP4i07/Fpo1tREhLpLzY88Xz6k+myX2MA5K+kmkshS0HvPJS9Uptg6uIC01eC/TNs9hRLCmScsaARty3gBiefV1l2c9jSKvoC2cMlxClEXVPzLqWvxiD+tE19KsTO+O31OzJWiHxllU47ft8XjGdoKCnPHajJ3 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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. Signed-off-by: Tejun Heo --- kernel/sched/build_policy.c | 4 ++ kernel/sched/ext.c | 11 ++++ kernel/sched/ext_arena.c | 127 ++++++++++++++++++++++++++++++++++++ kernel/sched/ext_arena.h | 18 +++++ kernel/sched/ext_internal.h | 5 ++ 5 files changed, 165 insertions(+) create mode 100644 kernel/sched/ext_arena.c create mode 100644 kernel/sched/ext_arena.h diff --git a/kernel/sched/build_policy.c b/kernel/sched/build_policy.c index 5e76c9177d54..067979a7b69e 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 56f94ac32ba0..fb91079c1244 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 000000000000..53174033765d --- /dev/null +++ b/kernel/sched/ext_arena.c @@ -0,0 +1,127 @@ +/* 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; + + kern_va = gen_pool_alloc(sch->arena_pool, size); + if (!kern_va) { + page_cnt = max_t(u32, SCX_ARENA_GROW_PAGES, + (size + PAGE_SIZE - 1) >> PAGE_SHIFT); + if (scx_arena_grow(sch, page_cnt)) + return NULL; + kern_va = gen_pool_alloc(sch->arena_pool, size); + if (!kern_va) + 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 000000000000..4f3610160102 --- /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 d40cfd29ddaa..ff7e882bd67a 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); -- 2.54.0