From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from firstgate.proxmox.com (firstgate.proxmox.com [IPv6:2a01:7e0:0:424::9]) by lore.proxmox.com (Postfix) with ESMTPS id 437771FF13F for ; Thu, 26 Mar 2026 07:16:44 +0100 (CET) Received: from firstgate.proxmox.com (localhost [127.0.0.1]) by firstgate.proxmox.com (Proxmox) with ESMTP id 0238658B4; Thu, 26 Mar 2026 07:17:04 +0100 (CET) Message-ID: <03fc2a07-34c8-4029-bbed-f1c764d4562e@proxmox.com> Date: Thu, 26 Mar 2026 07:16:29 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC] Re-enable alternative memory allocator (tcmalloc) for pve-qemu? To: Kefu Chai , pve-devel@lists.proxmox.com References: Content-Language: en-US From: Dietmar Maurer In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Bm-Milter-Handled: 55990f41-d878-4baa-be0a-ee34c49e34d2 X-Bm-Transport-Timestamp: 1774505742057 X-SPAM-LEVEL: Spam detection results: 0 AWL 0.337 Adjusted score from AWL reputation of From: address BAYES_00 -1.9 Bayes spam probability is 0 to 1% DMARC_MISSING 0.1 Missing DMARC policy KAM_DMARC_STATUS 0.01 Test Rule for DKIM or SPF Failure with Strict Alignment RCVD_IN_VALIDITY_CERTIFIED_BLOCKED 0.001 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. RCVD_IN_VALIDITY_RPBL_BLOCKED 0.001 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. RCVD_IN_VALIDITY_SAFE_BLOCKED 0.001 ADMINISTRATOR NOTICE: The query to Validity was blocked. See https://knowledge.validity.com/hc/en-us/articles/20961730681243 for more information. SPF_HELO_NONE 0.001 SPF: HELO does not publish an SPF Record SPF_PASS -0.001 SPF: sender matches SPF record Message-ID-Hash: 7QCJQGE77PSZNDF5G4GRH62I6JJ7AJHK X-Message-ID-Hash: 7QCJQGE77PSZNDF5G4GRH62I6JJ7AJHK X-MailFrom: dietmar@proxmox.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; loop; banned-address; emergency; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header X-Mailman-Version: 3.3.10 Precedence: list List-Id: Proxmox VE development discussion List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: > The mechanism is well-understood: librbd creates many small temporary > objects per I/O operation, and glibc's allocator is slow under that > fragmentation pattern. Such things are usually easy to fix using by using a custom pool allocator, freeing all allocated objects at once. But I don't know the Ceph code, so I am not sure if it is possible to apply such pattern to the Ceph code ... > But both allocators provide explicit "release everything now" APIs: > > - gperftools: MallocExtension::instance()->ReleaseFreeMemory() > (calls ReleaseToSystem(LONG_MAX) internally) > - jemalloc: mallctl("arena..purge", ...) The problem with that is that it can halt/delay the whole application while freeing memory? We need to make sure that there is no noticeable delay. > ## Questions for the team > > 1. Does anyone remember why tcmalloc was removed after only 8 days > in 2015 (2.3-4)? The changelog just says "remove tcmalloc" with > no explanation. Not really, sorry. > 2. Fiona: given the backup memory reclamation work in 5f9cb29, would > you see a problem with replacing malloc_trim with the > allocator-specific release API in the backup completion path? > > 3. Has the proxmox-backup-qemu library's allocation pattern changed > since 2020 in ways that might affect this? (e.g., different buffer > management, Rust allocator changes) I am not aware of such changes.