From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-186.mta1.migadu.com (out-186.mta1.migadu.com [95.215.58.186]) (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 6554210E3 for ; Thu, 28 Dec 2023 00:49:50 +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="XaxNWeJo" Message-ID: <4e19d402-ee59-42e3-be27-838d834d3477@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1703724588; 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=9i19dPoGIuLs7roVLcxtYB3uFpdkh5lUpBaLUlaxSvg=; b=XaxNWeJoRWotifKXHnW9hIEu56V36k3k5EyIFLdKBIiVhU/HQjc7Gqbexr6mZOIIffgEnL 11IHk851BoOKMCRTJidxkSUR/8J2DSKCuv7RMnqZZmiOaltmkmkobmeEUgx5V2tF+hLVQU 9byXpMU1RvQU6Uk1eZ91bkLFJiBs884= Date: Wed, 27 Dec 2023 16:49:40 -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 v6 0/8] bpf: Reduce memory usage for bpf_global_percpu_ma To: Hou Tao , bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , kernel-team@fb.com, Martin KaFai Lau References: <20231222031729.1287957-1-yonghong.song@linux.dev> Content-Language: en-GB X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Yonghong Song In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On 12/22/23 1:35 AM, Hou Tao wrote: > Hi, > > On 12/22/2023 11:17 AM, Yonghong Song wrote: >> Currently when a bpf program intends to allocate memory for percpu kptr, >> the verifier will call bpf_mem_alloc_init() to prefill all supported >> unit sizes and this caused memory consumption very big for large number >> of cpus. For example, for 128-cpu system, the total memory consumption >> with initial prefill is ~175MB. Things will become worse for systems >> with even more cpus. >> >> Patch 1 avoids unnecessary extra percpu memory allocation. >> Patch 2 adds objcg to bpf_mem_alloc at init stage so objcg can be >> associated with root cgroup and objcg can be passed to later >> bpf_mem_alloc_percpu_unit_init(). >> Patch 3 addresses memory consumption issue by avoiding to prefill >> with all unit sizes, i.e. only prefilling with user specified size. >> Patch 4 further reduces memory consumption by limiting the >> number of prefill entries for percpu memory allocation. >> Patch 5 has much smaller low/high watermarks for percpu allocation >> to reduce memory consumption. >> Patch 6 rejects percpu memory allocation with bpf_global_percpu_ma >> when allocation size is greater than 512 bytes. >> Patch 7 fixed test_bpf_ma test due to Patch 5. >> Patch 8 added one test to show the verification failure log message. > FYI. After applying the patch set, the memory consumption in bpf memory > benchmark [1] on 8-CPU VM decreases a lot: > > Before the patch set: > > $ for i in 1 4 8; do ./bench -w3 -d10 bpf_ma -p${i} -a --percpu; done | > grep Summary > Summary: per-prod alloc   14.16 ± 0.59M/s free   36.18 ± 0.39M/s, total > memory usage  183.71 ± 10.38MiB > Summary: per-prod alloc   12.35 ± 1.10M/s free   35.79 ± 0.51M/s, total > memory usage  744.52 ± 11.64MiB > Summary: per-prod alloc   11.15 ± 0.20M/s free   35.72 ± 0.27M/s, total > memory usage 2545.98 ± 537.57MiB > > After the patch set: > > $ for i in 1 4 8; do ./bench -w3 -d10 bpf_ma -p${i} -a --percpu; done | > grep Summary > Summary: per-prod alloc    0.86 ± 0.00M/s free   37.29 ± 0.11M/s, total > memory usage    0.00 ± 0.00MiB > Summary: per-prod alloc    0.85 ± 0.00M/s free   36.70 ± 0.24M/s, total > memory usage    0.00 ± 0.00MiB > Summary: per-prod alloc    0.84 ± 0.00M/s free   37.21 ± 0.17M/s, total > memory usage    0.00 ± 0.00MiB > > However the allocation performance also degrades a lot. It seems it is > due to patch 5 (bpf: Use smaller low/high marks for percpu allocation), > because c->batch is 1 now, so each allocation needs one run of irq_work. Thanks for benchmarking! With low watermark to be 1 and c->batch to 1 as well, there will be more overhead due to irq_work. In practice, I expect we should not see a lot of such percpu map element updates or percpu kptr allocaitons. > > [1]: > https://lore.kernel.org/bpf/20231221141501.3588586-1-houtao@huaweicloud.com/ >> Changelogs: >> v5 -> v6: >> . Change bpf_mem_alloc_percpu_init() to add objcg as one of parameters. >> For bpf_global_percpu_ma, the objcg is NULL, corresponding root memcg. >> v4 -> v5: >> . Do not do bpf_global_percpu_ma initialization at init stage, instead >> doing initialization when the verifier knows it is going to be used >> by bpf prog. >> . Using much smaller low/high watermarks for percpu allocation. >> v3 -> v4: >> . Add objcg to bpf_mem_alloc during init stage. >> . Initialize objcg at init stage but use it in bpf_mem_alloc_percpu_unit_init(). >> . Remove check_obj_size() in bpf_mem_alloc_percpu_unit_init(). >> v2 -> v3: >> . Clear the bpf_mem_cache if prefill fails. >> . Change test_bpf_ma percpu allocation tests to use bucket_size >> as allocation size instead of bucket_size - 8. >> . Remove __GFP_ZERO flag from __alloc_percpu_gfp() call. >> v1 -> v2: >> . Avoid unnecessary extra percpu memory allocation. >> . Add a separate function to do bpf_global_percpu_ma initialization >> . promote. >> . Promote function static 'sizes' array to file static. >> . Add comments to explain to refill only one item for percpu alloc. >> >> Yonghong Song (8): >> bpf: Avoid unnecessary extra percpu memory allocation >> bpf: Add objcg to bpf_mem_alloc >> bpf: Allow per unit prefill for non-fix-size percpu memory allocator >> bpf: Refill only one percpu element in memalloc >> bpf: Use smaller low/high marks for percpu allocation >> bpf: Limit up to 512 bytes for bpf_global_percpu_ma allocation >> selftests/bpf: Cope with 512 bytes limit with bpf_global_percpu_ma >> selftests/bpf: Add a selftest with > 512-byte percpu allocation size >> >> include/linux/bpf_mem_alloc.h | 8 ++ >> kernel/bpf/memalloc.c | 93 ++++++++++++++++--- >> kernel/bpf/verifier.c | 45 ++++++--- >> .../selftests/bpf/prog_tests/test_bpf_ma.c | 20 ++-- >> .../selftests/bpf/progs/percpu_alloc_fail.c | 18 ++++ >> .../testing/selftests/bpf/progs/test_bpf_ma.c | 66 ++++++------- >> 6 files changed, 184 insertions(+), 66 deletions(-) >>