From mboxrd@z Thu Jan 1 00:00:00 1970 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 lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id D00DCCD6E43 for ; Fri, 29 May 2026 02:35:29 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wSn3t-0002ZX-Md; Thu, 28 May 2026 22:35:01 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wSn3o-0002Z3-RA for qemu-devel@nongnu.org; Thu, 28 May 2026 22:34:56 -0400 Received: from [115.124.30.130] (helo=out30-130.freemail.mail.aliyun.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wSn3i-0008Mj-Ad for qemu-devel@nongnu.org; Thu, 28 May 2026 22:34:56 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1780022069; h=From:To:Subject:Date:Message-ID:MIME-Version; bh=pjtaOls1ii9JKGuurRt5ksb8LEZDgW05wpiuRF7AcZw=; b=VaDc8Hn1xNgkdyBehf6GKqJdJ+XGIl7I+g5Ti1HT1JTaNqMFgLVEi24cTyKcGQpODPJhXXrkyqqzjIT7vlRlTExKleA2J6+hWQACx/PZOZPStpjV4nDpSv1BVcOmZgrBAUeHv8NqdPXQZvPWwLVv+v2vEHGe1YQm+Qv8cyF03PM= X-Alimail-AntiSpam: AC=PASS; BC=-1|-1; BR=01201311R121e4; CH=green; DM=||false|; DS=||; FP=0|-1|-1|-1|0|-1|-1|-1; HT=maildocker-contentspam011083073210; MF=guobin@linux.alibaba.com; NM=1; PH=DS; RN=2; SR=0; TI=SMTPD_---0X3o2.Fu_1780022067; Received: from localhost(mailfrom:guobin@linux.alibaba.com fp:SMTPD_---0X3o2.Fu_1780022067 cluster:ay36) by smtp.aliyun-inc.com; Fri, 29 May 2026 10:34:27 +0800 From: Bin Guo To: qemu-devel@nongnu.org Cc: armbru@redhat.com Subject: [PATCH] qobject/json-writer: preallocate output buffer Date: Fri, 29 May 2026 10:34:26 +0800 Message-ID: <20260529023426.54680-1-guobin@linux.alibaba.com> X-Mailer: git-send-email 2.50.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Host-Lookup-Failed: Reverse DNS lookup failed for 115.124.30.130 (deferred) Received-SPF: pass client-ip=115.124.30.130; envelope-from=guobin@linux.alibaba.com; helo=out30-130.freemail.mail.aliyun.com X-Spam_score_int: -166 X-Spam_score: -16.7 X-Spam_bar: ---------------- X-Spam_report: (-16.7 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, ENV_AND_HDR_SPF_MATCH=-0.5, RCVD_IN_DNSWL_NONE=-0.0001, RDNS_NONE=0.793, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, UNPARSEABLE_RELAY=0.001, USER_IN_DEF_DKIM_WL=-7.5, USER_IN_DEF_SPF_WL=-7.5 autolearn=no autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org json_writer_new() creates the output GString with g_string_new(NULL), which starts at the GLib default of 64 bytes. Serializing typical QMP responses then requires multiple reallocations as the buffer grows -- for query-qmp-schema the GString is reallocated 12+ times. Preallocate JSON_WRITER_INITIAL_SIZE (4096) bytes. This covers most QMP responses without any reallocation. 4096 is one page on most systems, which is efficient for the allocator. The JSONWriter is a short-lived object so the preallocation does not accumulate. Signed-off-by: Bin Guo --- qobject/json-writer.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/qobject/json-writer.c b/qobject/json-writer.c index aac2c6ab71..fb3f3f3e3c 100644 --- a/qobject/json-writer.c +++ b/qobject/json-writer.c @@ -24,13 +24,16 @@ struct JSONWriter { GByteArray *container_is_array; }; +/* Covers most QMP responses without reallocation (one page) */ +#define JSON_WRITER_INITIAL_SIZE 4096 + JSONWriter *json_writer_new(bool pretty) { JSONWriter *writer = g_new(JSONWriter, 1); writer->pretty = pretty; writer->need_comma = false; - writer->contents = g_string_new(NULL); + writer->contents = g_string_sized_new(JSON_WRITER_INITIAL_SIZE); writer->container_is_array = g_byte_array_new(); return writer; } -- 2.50.1 (Apple Git-155)