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 105B4CD4F52 for ; Mon, 18 May 2026 11:01:53 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1wOvj0-0006ah-L1; Mon, 18 May 2026 07:01:30 -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 1wOviw-0006YN-PL for qemu-devel@nongnu.org; Mon, 18 May 2026 07:01:26 -0400 Received: from out30-119.freemail.mail.aliyun.com ([115.124.30.119]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1wOvit-0005hy-6x for qemu-devel@nongnu.org; Mon, 18 May 2026 07:01:26 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.alibaba.com; s=default; t=1779102076; h=From:To:Subject:Date:Message-ID:MIME-Version; bh=oli3TV2O+h3vqz3L6ihhLNIlHjx7t0sun6devc9rBO4=; b=SlROCCkpTXB3cWLe+QK3+vix5MHdCuPJn4bs9kztoLoxPkQOFnEQDdVz4craM+66mxKiT97pHxJPooORf4FWJAOhjnZ2oc0rECCs6k/4Zab5v31XNS9KYHtpF5S424SPD/6a1vgjTOXI22A5RUGbTdbphfviS8WeQtPotyMr3p8= X-Alimail-AntiSpam: AC=PASS; BC=-1|-1; BR=01201311R201e4; CH=green; DM=||false|; DS=||; FP=0|-1|-1|-1|0|-1|-1|-1; HT=maildocker-contentspam033037009110; MF=guobin@linux.alibaba.com; NM=1; PH=DS; RN=3; SR=0; TI=SMTPD_---0X38-onF_1779102075; Received: from localhost(mailfrom:guobin@linux.alibaba.com fp:SMTPD_---0X38-onF_1779102075 cluster:ay36) by smtp.aliyun-inc.com; Mon, 18 May 2026 19:01:15 +0800 From: Bin Guo To: qemu-devel@nongnu.org Cc: peterx@redhat.com, farosas@suse.de Subject: [PATCH 3/8] migration/vmstate: avoid per-element heap churn in vmsd ptr marker field Date: Mon, 18 May 2026 19:01:07 +0800 Message-ID: <20260518110112.21395-4-guobin@linux.alibaba.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20260518110112.21395-1-guobin@linux.alibaba.com> References: <20260518110112.21395-1-guobin@linux.alibaba.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=115.124.30.119; envelope-from=guobin@linux.alibaba.com; helo=out30-119.freemail.mail.aliyun.com X-Spam_score_int: -174 X-Spam_score: -17.5 X-Spam_bar: ----------------- X-Spam_report: (-17.5 / 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, 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=ham 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 For every NULL slot in a VMS_ARRAY_OF_POINTER (or every entry of a dynamic array), the saver allocates a 1-element fake VMStateField via g_new0 and frees it again right after the save. For arrays of thousands of entries this is thousands of malloc/free pairs on the hot save path. Replace the heap-allocated marker with a stack-resident field populated by an init helper. The caller passes a pointer to a local VMStateField, the helper fills it in (still asserting the precondition), and no g_free is needed. Signed-off-by: Bin Guo --- migration/vmstate.c | 41 ++++++++++++++++------------------------- 1 file changed, 16 insertions(+), 25 deletions(-) diff --git a/migration/vmstate.c b/migration/vmstate.c index 2f13b48a37..9ced78532f 100644 --- a/migration/vmstate.c +++ b/migration/vmstate.c @@ -59,29 +59,23 @@ vmstate_field_exists(const VMStateDescription *vmsd, const VMStateField *field, * array of a VMS_ARRAY_OF_POINTER VMSD field. It's needed because we * can't dereference the NULL pointer. */ -static const VMStateField * -vmsd_create_ptr_marker_field(const VMStateField *field) +static void +vmsd_init_ptr_marker_field(VMStateField *fake, const VMStateField *field) { - VMStateField *fake = g_new0(VMStateField, 1); - /* It can only happen on an array of pointers! */ assert(field->flags & VMS_ARRAY_OF_POINTER); - /* Some of fake's properties should match the original's */ - fake->name = field->name; - fake->version_id = field->version_id; - - /* Do not need "field_exists" check as it always exists */ - fake->field_exists = NULL; - - /* See vmstate_info_ptr_marker - use 1 byte to represent ptr status */ - fake->size = 1; - fake->info = &vmstate_info_ptr_marker; - fake->flags = VMS_SINGLE; - - /* All the rest fields shouldn't matter.. */ - - return (const VMStateField *)fake; + /* See vmstate_info_ptr_marker - 1 byte represents ptr status */ + *fake = (VMStateField) { + .name = field->name, + .version_id = field->version_id, + /* Marker always exists, no field_exists callback needed */ + .field_exists = NULL, + .size = 1, + .info = &vmstate_info_ptr_marker, + .flags = VMS_SINGLE, + /* All other fields stay zero-initialised */ + }; } static int vmstate_n_elems(void *opaque, const VMStateField *field) @@ -680,6 +674,7 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd, for (i = 0; i < n_elems; i++) { void *curr_elem = first_elem + size * i; const VMStateField *inner_field; + VMStateField marker_field; /* maximum number of elements to compress in the JSON blob */ int max_elems = vmsd_can_compress(field) ? (n_elems - i) : 1; bool use_marker_field, is_null = false; @@ -693,7 +688,8 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd, use_marker_field = use_dynamic_array || is_null; if (use_marker_field) { - inner_field = vmsd_create_ptr_marker_field(field); + vmsd_init_ptr_marker_field(&marker_field, field); + inner_field = &marker_field; } else { inner_field = field; } @@ -730,11 +726,6 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd, inner_field, vmdesc_loop, i, max_elems, errp); - /* If we used a fake temp field.. free it now */ - if (use_marker_field) { - g_clear_pointer((gpointer *)&inner_field, g_free); - } - if (!ok) { goto out; } -- 2.50.1 (Apple Git-155)