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9 Nov 2021 22:33:17 +0000 Message-ID: <03e480f8-c6c5-3247-5726-8982b02123af@oracle.com> Date: Tue, 9 Nov 2021 16:33:11 -0600 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.2.1 Subject: Re: [PATCH v2] Remove upper limit on tunable MALLOC_MMAP_THRESHOLD Content-Language: en-US To: DJ Delorie Cc: libc-alpha@sourceware.org References: From: Patrick McGehearty In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: SN6PR16CA0054.namprd16.prod.outlook.com (2603:10b6:805:ca::31) To BYAPR10MB3208.namprd10.prod.outlook.com (2603:10b6:a03:159::10) MIME-Version: 1.0 Received: from [10.39.245.196] (138.3.201.4) by SN6PR16CA0054.namprd16.prod.outlook.com (2603:10b6:805:ca::31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4669.10 via Frontend Transport; Tue, 9 Nov 2021 22:33:16 +0000 X-MS-PublicTrafficType: Email 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List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 09 Nov 2021 22:33:24 -0000 If a chunk smaller than the mmap_threshold is requested, then MORECORE [typically sbrk()] is called and HEAP_MAX is not considered by the malloc code.  Heaps are only used for mmap()ed allocations, not sbrk()'ed allocations, so far as I can tell in reading the code. Setting a higher default HEAP_MAX would mean the main arena would by default be larger which might cause issues for applications with many, many threads. For that reason, I did not consider changing the default HEAP_MAX as part of this patch. It might be desirable to also allow HEAP_MAX to be set by the user before the first call to malloc, but I see that as a separate task. -  patrick On 11/1/2021 7:27 PM, DJ Delorie wrote: > If mmap_threshold is greater than heap_max, what happens when you > allocate a chunk between those two sizes? >