From patchwork Tue Apr 8 16:05:08 2025 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Mathieu Desnoyers X-Patchwork-Id: 14043318 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 119F5C369A2 for ; Tue, 8 Apr 2025 16:05:19 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 328056B0093; Tue, 8 Apr 2025 12:05:17 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2FEAA6B0095; Tue, 8 Apr 2025 12:05:17 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 178376B0096; Tue, 8 Apr 2025 12:05:17 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) by kanga.kvack.org (Postfix) with ESMTP id E4B356B0093 for ; Tue, 8 Apr 2025 12:05:16 -0400 (EDT) Received: from smtpin14.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay07.hostedemail.com (Postfix) with ESMTP id DEEE61611B9 for ; Tue, 8 Apr 2025 16:05:17 +0000 (UTC) X-FDA: 83311351074.14.9AB23B6 Received: from smtpout.efficios.com (smtpout.efficios.com [158.69.130.18]) by imf03.hostedemail.com (Postfix) with ESMTP id E4A5F20009 for ; Tue, 8 Apr 2025 16:05:15 +0000 (UTC) Authentication-Results: imf03.hostedemail.com; dkim=pass header.d=efficios.com header.s=smtpout1 header.b=DMJNR1lt; dmarc=pass (policy=none) header.from=efficios.com; spf=pass (imf03.hostedemail.com: domain of mathieu.desnoyers@efficios.com designates 158.69.130.18 as permitted sender) smtp.mailfrom=mathieu.desnoyers@efficios.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1744128316; h=from:from:sender: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: references:dkim-signature; bh=eLyne7m0C417zu3+EbeQgzSDOFKUX+Dlvx0uVu7+NsY=; b=w3OOoDAafhPCmJAepVUkcGJovIL8bRk2JfHb7ZNEKWLs6SwVywXymeUdl8H0Ql+Xv3qD3q 7AyxlNYmCObg4Nb9BOmdTU3NvHdy+a+fBnGoaYLV5Us5MlVifiS3tCMNTP778F3EKGL7Bv Rj85U3rz8LjpQEC041SQ22MnLUPAITY= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1744128316; a=rsa-sha256; cv=none; b=Wx3/eOdrVMGrZ3KhgL4sE5dqKPDX9SFAhy/jiyPwtSdCJvW580NeUzfJjvd3S4xPfAfsaU r9LaPxvAvCGyKRBvVSQAXbVrIwUWrtCCTOs2EohM7tXJapZgkB0JP1viH8PYHpnq2WeKLP isFlyPIrBVN4giWT5kX1vDQaH0h1JBs= ARC-Authentication-Results: i=1; imf03.hostedemail.com; dkim=pass header.d=efficios.com header.s=smtpout1 header.b=DMJNR1lt; dmarc=pass (policy=none) header.from=efficios.com; spf=pass (imf03.hostedemail.com: domain of mathieu.desnoyers@efficios.com designates 158.69.130.18 as permitted sender) smtp.mailfrom=mathieu.desnoyers@efficios.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=efficios.com; s=smtpout1; t=1744128315; bh=30nP+t9oyZ1F0fRLjqbXH1OPlVwPLFQRPahG/PJCRkI=; h=From:To:Cc:Subject:Date:From; b=DMJNR1ltTOJSyotfY1foVwYw+MAd6XhPR9Kyl1q0uADQ2SJqbuiOIbRzs8ITyqfL5 sc0xyB0k9CFAi3Kmyy9ycS0RWXW6QpJnDsGQvUH4TUCPEGtpyvvcsIO1FFK1HT3THS rLFEGRfU2qtbWlEaqY64sIaIP+LIOvRBzfJPwdqxZuBx/uQiRZ+He5iajdXVfoHqJH g18vn1KEOKtSbq/AZKXsfLB+rC8vGSbpu6Qpd4nhU55UQEuss8GRg5A9Y8BWqjt87O Dr8ZIJpreMtMNf8oJkeZ4mOFf5dbk8987H5mmjYx7F9sN2nfDaS+V3RqDldb+NDs8A d+QY8UCldvm8Q== Received: from thinkos.internal.efficios.com (96-127-217-162.qc.cable.ebox.net [96.127.217.162]) by smtpout.efficios.com (Postfix) with ESMTPSA id 4ZX9s63lBPz1Cv3; Tue, 8 Apr 2025 12:05:14 -0400 (EDT) From: Mathieu Desnoyers To: Sweet Tea Dorminy , Mateusz Guzik Cc: linux-kernel@vger.kernel.org, Mathieu Desnoyers , Andrew Morton , "Paul E. McKenney" , Steven Rostedt , Masami Hiramatsu , Dennis Zhou , Tejun Heo , Christoph Lameter , Martin Liu , David Rientjes , christian.koenig@amd.com, Shakeel Butt , Johannes Weiner , Lorenzo Stoakes , "Liam R . Howlett" , Suren Baghdasaryan , Vlastimil Babka , Christian Brauner , Wei Yang , David Hildenbrand , Miaohe Lin , Al Viro , linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org, Yu Zhao , Roman Gushchin , Matthew Wilcox Subject: [RFC PATCH v2] Introduce Hierarchical Per-CPU Counters Date: Tue, 8 Apr 2025 12:05:08 -0400 Message-Id: <20250408160508.991738-1-mathieu.desnoyers@efficios.com> X-Mailer: git-send-email 2.39.5 MIME-Version: 1.0 X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: E4A5F20009 X-Stat-Signature: b1su4cyw59mngwxi34gu8r7m4sfdqxs6 X-Rspam-User: X-HE-Tag: 1744128315-165286 X-HE-Meta: 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 /+nEN+04 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 rmtqAIgZ xl65sttSaWE= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: * Motivation The purpose of this hierarchical split-counter scheme is to: - Minimize contention when incrementing and decrementing counters, - Provide fast access to a sum approximation, - Provide a sum approximation with an acceptable accuracy level when scaling to many-core systems. - Provide approximate and precise comparison of two counters, and between a counter and a value. It aims at fixing the per-mm RSS tracking which has become too inaccurate for OOM killer purposes on large many-core systems [1]. * Design The hierarchical per-CPU counters propagate a sum approximation through a binary tree. When reaching the batch size, the carry is propagated through a binary tree which consists of log2(nr_cpu_ids) levels. The batch size for each level is twice the batch size of the prior level. Example propagation diagram with 8 cpus: Level 0: 0 1 2 3 4 5 6 7 | / | / | / | / | / | / | / | / | / | / | / | / Level 1: 0 1 2 3 | / | / | / | / | / | / Level 2: 0 1 | / | / | / Level 3: 0 The maximum inaccuracy is bound by: batch_size * log2(nr_cpus) * nr_cpus which evolves with O(n*log(n)) as the number of CPUs increases. Link: https://lore.kernel.org/lkml/20250331223516.7810-2-sweettea-kernel@dorminy.me/ # [1] Signed-off-by: Mathieu Desnoyers Cc: Andrew Morton Cc: "Paul E. McKenney" Cc: Steven Rostedt Cc: Masami Hiramatsu Cc: Mathieu Desnoyers Cc: Dennis Zhou Cc: Tejun Heo Cc: Christoph Lameter Cc: Martin Liu Cc: David Rientjes Cc: christian.koenig@amd.com Cc: Shakeel Butt Cc: Johannes Weiner Cc: Sweet Tea Dorminy Cc: Lorenzo Stoakes Cc: "Liam R . Howlett" Cc: Suren Baghdasaryan Cc: Vlastimil Babka Cc: Christian Brauner Cc: Wei Yang Cc: David Hildenbrand Cc: Miaohe Lin Cc: Al Viro Cc: linux-mm@kvack.org Cc: linux-trace-kernel@vger.kernel.org Cc: Yu Zhao Cc: Roman Gushchin Cc: Mateusz Guzik Cc: Matthew Wilcox --- Changes since v1: - Remove percpu_counter_tree_precise_sum_unbiased from public header, make this function static, - Introduce precise and approximate comparisons between two counters, - Reorder the struct percpu_counter_tree fields, - Introduce approx_sum field, which points to the approximate sum for the percpu_counter_tree_approximate_sum() fast path. --- include/linux/percpu_counter_tree.h | 102 +++++++++ lib/Makefile | 1 + lib/percpu_counter_tree.c | 313 ++++++++++++++++++++++++++++ 3 files changed, 416 insertions(+) create mode 100644 include/linux/percpu_counter_tree.h create mode 100644 lib/percpu_counter_tree.c diff --git a/include/linux/percpu_counter_tree.h b/include/linux/percpu_counter_tree.h new file mode 100644 index 000000000000..aac5a711de3e --- /dev/null +++ b/include/linux/percpu_counter_tree.h @@ -0,0 +1,102 @@ +/* SPDX-License-Identifier: GPL-2.0+ OR MIT */ +/* SPDX-FileCopyrightText: 2025 Mathieu Desnoyers */ + +#ifndef _PERCPU_COUNTER_TREE_H +#define _PERCPU_COUNTER_TREE_H + +#include +#include +#include +#include + +struct percpu_counter_tree_level_item { + atomic_t count; +} ____cacheline_aligned_in_smp; + +struct percpu_counter_tree { + /* Fast-path fields. */ + unsigned int __percpu *level0; + unsigned int level0_bit_mask; + atomic_t *approx_sum; + int bias; /* bias for counter_set */ + + /* Slow-path fields. */ + struct percpu_counter_tree_level_item *items; + unsigned int batch_size; + unsigned int inaccuracy; /* approximation imprecise within ± inaccuracy */ + unsigned int nr_levels; + unsigned int nr_cpus; +}; + +int percpu_counter_tree_init(struct percpu_counter_tree *counter, unsigned int batch_size); +void percpu_counter_tree_destroy(struct percpu_counter_tree *counter); +void percpu_counter_tree_add_slowpath(struct percpu_counter_tree *counter, int inc); +int percpu_counter_tree_precise_sum(struct percpu_counter_tree *counter); +int percpu_counter_tree_approximate_compare(struct percpu_counter_tree *a, struct percpu_counter_tree *b); +int percpu_counter_tree_approximate_compare_value(struct percpu_counter_tree *counter, int v); +int percpu_counter_tree_precise_compare(struct percpu_counter_tree *a, struct percpu_counter_tree *b); +int percpu_counter_tree_precise_compare_value(struct percpu_counter_tree *counter, int v); +void percpu_counter_tree_set_bias(struct percpu_counter_tree *counter, int bias); +void percpu_counter_tree_set(struct percpu_counter_tree *counter, int v); +unsigned int percpu_counter_tree_inaccuracy(struct percpu_counter_tree *counter); + +/* Fast paths */ + +static inline +int percpu_counter_tree_carry(int orig, int res, int inc, unsigned int bit_mask) +{ + if (inc < 0) { + inc = -(-inc & ~(bit_mask - 1)); + /* + * xor bit_mask: underflow. + * + * If inc has bit set, decrement an additional bit if + * there is _no_ bit transition between orig and res. + * Else, inc has bit cleared, decrement an additional + * bit if there is a bit transition between orig and + * res. + */ + if ((inc ^ orig ^ res) & bit_mask) + inc -= bit_mask; + } else { + inc &= ~(bit_mask - 1); + /* + * xor bit_mask: overflow. + * + * If inc has bit set, increment an additional bit if + * there is _no_ bit transition between orig and res. + * Else, inc has bit cleared, increment an additional + * bit if there is a bit transition between orig and + * res. + */ + if ((inc ^ orig ^ res) & bit_mask) + inc += bit_mask; + } + return inc; +} + +static inline +void percpu_counter_tree_add(struct percpu_counter_tree *counter, int inc) +{ + unsigned int bit_mask = counter->level0_bit_mask, orig, res; + + if (!inc) + return; + /* Make sure the fast and slow paths use the same cpu number. */ + guard(migrate)(); + res = this_cpu_add_return(*counter->level0, inc); + orig = res - inc; + inc = percpu_counter_tree_carry(orig, res, inc, bit_mask); + if (!inc) + return; + percpu_counter_tree_add_slowpath(counter, inc); +} + +static inline +int percpu_counter_tree_approximate_sum(struct percpu_counter_tree *counter) +{ + return (int) ((unsigned int)atomic_read(counter->approx_sum) + + (unsigned int)READ_ONCE(counter->bias)); +} + +#endif /* _PERCPU_COUNTER_TREE_H */ diff --git a/lib/Makefile b/lib/Makefile index d5cfc7afbbb8..d803a3a63288 100644 --- a/lib/Makefile +++ b/lib/Makefile @@ -201,6 +201,7 @@ obj-$(CONFIG_TEXTSEARCH_KMP) += ts_kmp.o obj-$(CONFIG_TEXTSEARCH_BM) += ts_bm.o obj-$(CONFIG_TEXTSEARCH_FSM) += ts_fsm.o obj-$(CONFIG_SMP) += percpu_counter.o +obj-$(CONFIG_SMP) += percpu_counter_tree.o obj-$(CONFIG_AUDIT_GENERIC) += audit.o obj-$(CONFIG_AUDIT_COMPAT_GENERIC) += compat_audit.o diff --git a/lib/percpu_counter_tree.c b/lib/percpu_counter_tree.c new file mode 100644 index 000000000000..b530ba9dd61b --- /dev/null +++ b/lib/percpu_counter_tree.c @@ -0,0 +1,313 @@ +// SPDX-License-Identifier: GPL-2.0+ OR MIT +// SPDX-FileCopyrightText: 2025 Mathieu Desnoyers + +/* + * Split Counters With Binary Tree Approximation Propagation + * + * * Propagation diagram when reaching batch size thresholds (± batch size): + * + * Example diagram for 8 CPUs: + * + * log2(8) = 3 levels + * + * At each level, each pair propagates its values to the next level when + * reaching the batch size thresholds. + * + * Counters at levels 0, 1, 2 can be kept on a single byte (±128 range), + * although it may be relevant to keep them on 32-bit counters for + * simplicity. (complexity vs memory footprint tradeoff) + * + * Counter at level 3 can be kept on a 32-bit counter. + * + * Level 0: 0 1 2 3 4 5 6 7 + * | / | / | / | / + * | / | / | / | / + * | / | / | / | / + * Level 1: 0 1 2 3 + * | / | / + * | / | / + * | / | / + * Level 2: 0 1 + * | / + * | / + * | / + * Level 3: 0 + * + * * Approximation inaccuracy: + * + * BATCH(level N): Level N batch size. + * + * Example for BATCH(level 0) = 32. + * + * BATCH(level 0) = 32 + * BATCH(level 1) = 64 + * BATCH(level 2) = 128 + * BATCH(level N) = BATCH(level 0) * 2^N + * + * per-counter global + * inaccuracy inaccuracy + * Level 0: [ -32 .. +31] ±256 (8 * 32) + * Level 1: [ -64 .. +63] ±256 (4 * 64) + * Level 2: [-128 .. +127] ±256 (2 * 128) + * Total: ------ ±768 (log2(nr_cpu_ids) * BATCH(level 0) * nr_cpu_ids) + * + * ----- + * + * Approximate Sum Carry Propagation + * + * Let's define a number of counter bits for each level, e.g.: + * + * log2(BATCH(level 0)) = log2(32) = 5 + * + * nr_bit value_mask range + * Level 0: 5 bits v 0 .. +31 + * Level 1: 1 bit (v & ~((1UL << 5) - 1)) 0 .. +63 + * Level 2: 1 bit (v & ~((1UL << 6) - 1)) 0 .. +127 + * Level 3: 25 bits (v & ~((1UL << 7) - 1)) 0 .. 2^32-1 + * + * Note: Use a full 32-bit per-cpu counter at level 0 to allow precise sum. + * + * Note: Use cacheline aligned counters at levels above 0 to prevent false sharing. + * If memory footprint is an issue, a specialized allocator could be used + * to eliminate padding. + * + * Example with expanded values: + * + * counter_add(counter, inc): + * + * if (!inc) + * return; + * + * res = percpu_add_return(counter @ Level 0, inc); + * orig = res - inc; + * if (inc < 0) { + * inc = -(-inc & ~0b00011111); // Clear used bits + * // xor bit 5: underflow + * if ((inc ^ orig ^ res) & 0b00100000) + * inc -= 0b00100000; + * } else { + * inc &= ~0b00011111; // Clear used bits + * // xor bit 5: overflow + * if ((inc ^ orig ^ res) & 0b00100000) + * inc += 0b00100000; + * } + * if (!inc) + * return; + * + * res = atomic_add_return(counter @ Level 1, inc); + * orig = res - inc; + * if (inc < 0) { + * inc = -(-inc & ~0b00111111); // Clear used bits + * // xor bit 6: underflow + * if ((inc ^ orig ^ res) & 0b01000000) + * inc -= 0b01000000; + * } else { + * inc &= ~0b00111111; // Clear used bits + * // xor bit 6: overflow + * if ((inc ^ orig ^ res) & 0b01000000) + * inc += 0b01000000; + * } + * if (!inc) + * return; + * + * res = atomic_add_return(counter @ Level 2, inc); + * orig = res - inc; + * if (inc < 0) { + * inc = -(-inc & ~0b01111111); // Clear used bits + * // xor bit 7: underflow + * if ((inc ^ orig ^ res) & 0b10000000) + * inc -= 0b10000000; + * } else { + * inc &= ~0b01111111; // Clear used bits + * // xor bit 7: overflow + * if ((inc ^ orig ^ res) & 0b10000000) + * inc += 0b10000000; + * } + * if (!inc) + * return; + * + * atomic_add(counter @ Level 3, inc); + */ + +#include +#include +#include +#include +#include +#include +#include + +int percpu_counter_tree_init(struct percpu_counter_tree *counter, unsigned int batch_size) +{ + /* Batch size must be power of 2 */ + if (!batch_size || (batch_size & (batch_size - 1))) + return -EINVAL; + counter->nr_levels = get_count_order(nr_cpu_ids); + counter->nr_cpus = 1UL << counter->nr_levels; + counter->batch_size = batch_size; + counter->level0_bit_mask = 1UL << get_count_order(batch_size); + counter->inaccuracy = counter->nr_levels * batch_size * counter->nr_cpus; + counter->bias = 0; + counter->level0 = alloc_percpu(unsigned int); + if (!counter->level0) + return -ENOMEM; + counter->items = kzalloc(counter->nr_cpus - 1 * + sizeof(struct percpu_counter_tree_level_item), + GFP_KERNEL); + if (!counter->items) { + free_percpu(counter->level0); + return -ENOMEM; + } + counter->approx_sum = &counter->items[counter->nr_cpus - 2].count; + return 0; +} + +void percpu_counter_tree_destroy(struct percpu_counter_tree *counter) +{ + free_percpu(counter->level0); + kfree(counter->items); +} + +/* Called with migration disabled. */ +void percpu_counter_tree_add_slowpath(struct percpu_counter_tree *counter, int inc) +{ + struct percpu_counter_tree_level_item *item = counter->items; + unsigned int level_items = counter->nr_cpus >> 1; + unsigned int level, nr_levels = counter->nr_levels; + unsigned int bit_mask = counter->level0_bit_mask; + unsigned int cpu = smp_processor_id(); + + for (level = 1; level < nr_levels; level++) { + atomic_t *count = &item[cpu & (level_items - 1)].count; + unsigned int orig, res; + + bit_mask <<= 1; + res = atomic_add_return_relaxed(inc, count); + orig = res - inc; + inc = percpu_counter_tree_carry(orig, res, inc, bit_mask); + item += level_items; + level_items >>= 1; + if (!inc) + return; + } + atomic_add(inc, counter->approx_sum); +} + +/* + * Precise sum. Perform the sum of all per-cpu counters. + */ +static +int percpu_counter_tree_precise_sum_unbiased(struct percpu_counter_tree *counter) +{ + unsigned int sum = 0; + int cpu; + + for_each_possible_cpu(cpu) + sum += *per_cpu_ptr(counter->level0, cpu); + return (int) sum; +} + +int percpu_counter_tree_precise_sum(struct percpu_counter_tree *counter) +{ + return percpu_counter_tree_precise_sum_unbiased(counter) + READ_ONCE(counter->bias); +} + +/* + * Do an approximate comparison of two counters. + * Return 0 if counters do not differ by more than the sum of their + * respective inaccuracy ranges, + * Return -1 if counter @a less than counter @b, + * Return 1 if counter @a is greater than counter @b. + */ +int percpu_counter_tree_approximate_compare(struct percpu_counter_tree *a, struct percpu_counter_tree *b) +{ + int count_a = percpu_counter_tree_approximate_sum(a), + count_b = percpu_counter_tree_approximate_sum(b); + + if (abs(count_a - count_b) <= (a->inaccuracy + b->inaccuracy)) + return 0; + if (count_a < count_b) + return -1; + return 1; +} + +/* + * Do an approximate comparison of a counter against a given value. + * Return 0 if the value is within the inaccuracy range of the counter, + * Return -1 if the value less than counter, + * Return 1 if the value is greater than counter. + */ +int percpu_counter_tree_approximate_compare_value(struct percpu_counter_tree *counter, int v) +{ + int count = percpu_counter_tree_approximate_sum(counter); + + if (abs(v - count) <= counter->inaccuracy) + return 0; + if (count < v) + return -1; + return 1; +} + +/* + * Do a precise comparison of two counters. + * Return 0 if the counters are equal, + * Return -1 if counter @a less than counter @b, + * Return 1 if counter @a is greater than counter @b. + */ +int percpu_counter_tree_precise_compare(struct percpu_counter_tree *a, struct percpu_counter_tree *b) +{ + int count_a = percpu_counter_tree_approximate_sum(a), + count_b = percpu_counter_tree_approximate_sum(b); + + if (abs(count_a - count_b) <= (a->inaccuracy + b->inaccuracy)) { + if (b->inaccuracy < a->inaccuracy) { + count_a = percpu_counter_tree_precise_sum(a); + if (abs(count_a - count_b) <= b->inaccuracy) + count_b = percpu_counter_tree_precise_sum(b); + } else { + count_b = percpu_counter_tree_precise_sum(b); + if (abs(count_a - count_b) <= a->inaccuracy) + count_a = percpu_counter_tree_precise_sum(a); + } + } + if (count_a > count_b) + return -1; + if (count_a > count_b) + return 1; + return 0; +} + +/* + * Do a precise comparision of a counter against a given value. + * Return 0 if the value is equal to the counter, + * Return -1 if the value less than counter, + * Return 1 if the value is greater than counter. + */ +int percpu_counter_tree_precise_compare_value(struct percpu_counter_tree *counter, int v) +{ + int count = percpu_counter_tree_approximate_sum(counter); + + if (abs(v - count) <= counter->inaccuracy) + count = percpu_counter_tree_precise_sum(counter); + if (count < v) + return -1; + if (count > v) + return 1; + return 0; +} + +void percpu_counter_tree_set_bias(struct percpu_counter_tree *counter, int bias) +{ + WRITE_ONCE(counter->bias, bias); +} + +void percpu_counter_tree_set(struct percpu_counter_tree *counter, int v) +{ + percpu_counter_tree_set_bias(counter, + v - percpu_counter_tree_precise_sum_unbiased(counter)); +} + +unsigned int percpu_counter_tree_inaccuracy(struct percpu_counter_tree *counter) +{ + return counter->inaccuracy; +}