From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-184.mta1.migadu.com (out-184.mta1.migadu.com [95.215.58.184]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 03EB7156C9 for ; Thu, 21 Dec 2023 07:52:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="X0TwC4Mm" Message-ID: <2c6e0258-8ecf-4acd-9cb9-8b9ac6222794@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1703145160; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=1d2ceve+3phxZ9nH7IW39aBCY3ci1u9+TrsjLI8bNmk=; b=X0TwC4MmCQZsBSpyXIwcAAf5+IxgOPvFNiI1kmNNMN+si1OCnKiNYFXQxMW1z/hejPiZyV 9qvcDTLSNeQryNR8Iv3bWjK+NvRK0+ymg9g6AkjCHjeqw111Gz4rGpu4Lhu/+2BDMJd98E WMQKBBgMYbqXnpRA00qGEkcJ09+hejo= Date: Wed, 20 Dec 2023 23:52:33 -0800 Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Subject: Re: [PATCH bpf-next v5 3/8] bpf: Allow per unit prefill for non-fix-size percpu memory allocator Content-Language: en-GB X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song To: Hou Tao , bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , kernel-team@fb.com, Martin KaFai Lau References: <20231221045954.1969955-1-yonghong.song@linux.dev> <20231221050010.1971932-1-yonghong.song@linux.dev> <58e11994-6f73-20de-eab8-f4d7a4f71d80@huaweicloud.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 12/20/23 11:16 PM, Yonghong Song wrote: > > On 12/20/23 10:26 PM, Hou Tao wrote: >> Hi, >> >> On 12/21/2023 1:00 PM, Yonghong Song wrote: >>> Commit 41a5db8d8161 ("Add support for non-fix-size percpu mem >>> allocation") >>> added support for non-fix-size percpu memory allocation. >>> Such allocation will allocate percpu memory for all buckets on all >>> cpus and the memory consumption is in the order to quadratic. >>> For example, let us say, 4 cpus, unit size 16 bytes, so each >>> cpu has 16 * 4 = 64 bytes, with 4 cpus, total will be 64 * 4 = 256 >>> bytes. >>> Then let us say, 8 cpus with the same unit size, each cpu >>> has 16 * 8 = 128 bytes, with 8 cpus, total will be 128 * 8 = 1024 >>> bytes. >>> So if the number of cpus doubles, the number of memory consumption >>> will be 4 times. So for a system with large number of cpus, the >>> memory consumption goes up quickly with quadratic order. >>> For example, for 4KB percpu allocation, 128 cpus. The total memory >>> consumption will 4KB * 128 * 128 = 64MB. Things will become >>> worse if the number of cpus is bigger (e.g., 512, 1024, etc.) >>> >>> In Commit 41a5db8d8161, the non-fix-size percpu memory allocation is >>> done in boot time, so for system with large number of cpus, the initial >>> percpu memory consumption is very visible. For example, for 128 cpu >>> system, the total percpu memory allocation will be at least >>> (16 + 32 + 64 + 96 + 128 + 196 + 256 + 512 + 1024 + 2048 + 4096) >>>    * 128 * 128 = ~138MB. >>> which is pretty big. It will be even bigger for larger number of cpus. >> SNIP >>> + >>>   static void drain_mem_cache(struct bpf_mem_cache *c) >>>   { >>>       bool percpu = !!c->percpu_size; >>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c >>> index f13008d27f35..08f9a49cc11c 100644 >>> --- a/kernel/bpf/verifier.c >>> +++ b/kernel/bpf/verifier.c >>> @@ -12141,20 +12141,6 @@ static int check_kfunc_call(struct >>> bpf_verifier_env *env, struct bpf_insn *insn, >>>                   if (meta.func_id == >>> special_kfunc_list[KF_bpf_obj_new_impl] && !bpf_global_ma_set) >>>                       return -ENOMEM; >>>   -                if (meta.func_id == >>> special_kfunc_list[KF_bpf_percpu_obj_new_impl]) { >>> -                    if (!bpf_global_percpu_ma_set) { >>> -                        mutex_lock(&bpf_percpu_ma_lock); >>> -                        if (!bpf_global_percpu_ma_set) { >>> -                            err = >>> bpf_mem_alloc_init(&bpf_global_percpu_ma, 0, true); >>> -                            if (!err) >>> -                                bpf_global_percpu_ma_set = true; >>> -                        } >>> - mutex_unlock(&bpf_percpu_ma_lock); >>> -                        if (err) >>> -                            return err; >>> -                    } >>> -                } >>> - >>>                   if (((u64)(u32)meta.arg_constant.value) != >>> meta.arg_constant.value) { >>>                       verbose(env, "local type ID argument must be >>> in range [0, U32_MAX]\n"); >>>                       return -EINVAL; >>> @@ -12175,6 +12161,26 @@ static int check_kfunc_call(struct >>> bpf_verifier_env *env, struct bpf_insn *insn, >>>                       return -EINVAL; >>>                   } >>>   +                if (meta.func_id == >>> special_kfunc_list[KF_bpf_percpu_obj_new_impl]) { >>> +                    if (!bpf_global_percpu_ma_set) { >>> +                        mutex_lock(&bpf_percpu_ma_lock); >>> +                        if (!bpf_global_percpu_ma_set) { >>> +                            err = >>> bpf_mem_alloc_percpu_init(&bpf_global_percpu_ma); >> Because ma->objcg is assigned as get_obj_cgroup_from_current(), so I >> think the memory account will be incorrect, right ? Maybe we should pass >> objcg to bpf_mem_alloc_percpu_init() explicit. For root memcg, I think >> the objcg is NULL. > > You are correct. Calling bpf_mem_alloc_percpu_init() in init stage > is exactly the reason to have proper root memcg for objcg. Sorry I > missed it. > > I remembered I indeed traced it a few days ago and indeed it is NULL. > There are three ways to resolve this: >    1 Just do 'ma->objcg = NULL' unconditionally in > bpf_mem_alloc_percpu_init(). >    2 Second, we can remember objcg = bpf_mem_alloc_percpu_init() at > init stage, >      e.g., in bpf_global_ma_init() init function (core.c), and later > it can >      be used in bpf_mem_alloc_percpu_init(). >    3 Still do bpf_mem_alloc_percpu_init() at init stage to initialize > ma->objcg >      properly. But delay __alloc_percpu_gfp() later when verifier > found a call >      to bpf_percpu_obj_new(). We could add a call > bpf_mem_alloc_percpu_init_caches() >      to do __alloc_percpu_grp(). > > I prefer option 3, what do you think? The option 4 below: diff --git a/kernel/bpf/memalloc.c b/kernel/bpf/memalloc.c index 984c83ecace9..f90989cc9cbc 100644 --- a/kernel/bpf/memalloc.c +++ b/kernel/bpf/memalloc.c @@ -122,6 +122,7 @@ struct bpf_mem_caches { }; static const u16 sizes[NUM_CACHES] = {96, 192, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096}; +static struct obj_cgroup *objcg_at_init __ro_after_init; static struct llist_node notrace *__llist_del_first(struct llist_head *head) { @@ -590,7 +591,7 @@ int bpf_mem_alloc_percpu_init(struct bpf_mem_alloc *ma) ma->percpu = true; #ifdef CONFIG_MEMCG_KMEM - ma->objcg = get_obj_cgroup_from_current(); + ma->objcg = objcg_at_init; #else ma->objcg = NULL; #endif @@ -1015,3 +1016,10 @@ void notrace *bpf_mem_cache_alloc_flags(struct bpf_mem_alloc *ma, gfp_t flags) return !ret ? NULL : ret + LLIST_NODE_SZ; } + +static int __init find_objcg_at_init(void) +{ + objcg_at_init = get_obj_cgroup_from_current(); + return 0; +} +late_initcall(find_objcg_at_init); It seems this is better? > >>> +                            if (!err) >>> +                                bpf_global_percpu_ma_set = true; >>> +                        } >>> + mutex_unlock(&bpf_percpu_ma_lock); >>> +                        if (err) >>> +                            return err; >>> +                    } >>> + >>> +                    mutex_lock(&bpf_percpu_ma_lock); >>> +                    err = >>> bpf_mem_alloc_percpu_unit_init(&bpf_global_percpu_ma, ret_t->size); >>> +                    mutex_unlock(&bpf_percpu_ma_lock); >>> +                    if (err) >>> +                        return err; >>> +                } >>> + >>>                   struct_meta = btf_find_struct_meta(ret_btf, >>> ret_btf_id); >>>                   if (meta.func_id == >>> special_kfunc_list[KF_bpf_percpu_obj_new_impl]) { >>>                       if (!__btf_type_is_scalar_struct(env, ret_btf, >>> ret_t, 0)) { >> >