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McKenney" , Joel Fernandes , Oleksiy Avramchenko , "kexec@lists.infradead.org" Subject: Re: [PATCH v2 4/9] mm: vmalloc: Remove global vmap_area_root rb-tree Thread-Topic: [PATCH v2 4/9] mm: vmalloc: Remove global vmap_area_root rb-tree Thread-Index: AQHZ4TGFXwcU9uXlJU+Gvi161nfs3rAPHBYAgAAFI4CAAQo/gA== Date: Fri, 8 Sep 2023 01:51:06 +0000 Message-ID: <8939ea67-ca27-1aa5-dfff-37d78ad59bb8@nec.com> References: <20230829081142.3619-1-urezki@gmail.com> <20230829081142.3619-5-urezki@gmail.com> In-Reply-To: Accept-Language: ja-JP, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: authentication-results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=nec.com; x-ms-publictraffictype: Email x-ms-traffictypediagnostic: TYYPR01MB6777:EE_|TYWPR01MB8637:EE_ x-ms-office365-filtering-correlation-id: ec98f486-7010-4d5a-400d-08dbb00e115b x-ms-exchange-senderadcheck: 1 x-ms-exchange-antispam-relay: 0 x-microsoft-antispam: BCL:0; x-microsoft-antispam-message-info: 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 x-forefront-antispam-report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:TYYPR01MB6777.jpnprd01.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230031)(136003)(346002)(396003)(366004)(376002)(39860400002)(186009)(1800799009)(451199024)(122000001)(38070700005)(38100700002)(82960400001)(36756003)(85182001)(86362001)(31696002)(478600001)(2906002)(110136005)(6512007)(55236004)(53546011)(4326008)(6506007)(6486002)(8676002)(8936002)(5660300002)(76116006)(66476007)(66946007)(66446008)(316002)(54906003)(31686004)(66556008)(64756008)(41300700001)(71200400001)(7416002)(83380400001)(26005)(2616005)(45980500001);DIR:OUT;SFP:1101; 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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+kexec=archiver.kernel.org@lists.infradead.org On 2023/09/07 18:58, Baoquan He wrote: > On 09/07/23 at 11:39am, Uladzislau Rezki wrote: >> On Thu, Sep 07, 2023 at 10:17:39AM +0800, Baoquan He wrote: >>> Add Kazu and Lianbo to CC, and kexec mailing list >>> >>> On 08/29/23 at 10:11am, Uladzislau Rezki (Sony) wrote: >>>> Store allocated objects in a separate nodes. A va->va_start >>>> address is converted into a correct node where it should >>>> be placed and resided. An addr_to_node() function is used >>>> to do a proper address conversion to determine a node that >>>> contains a VA. >>>> >>>> Such approach balances VAs across nodes as a result an access >>>> becomes scalable. Number of nodes in a system depends on number >>>> of CPUs divided by two. The density factor in this case is 1/2. >>>> >>>> Please note: >>>> >>>> 1. As of now allocated VAs are bound to a node-0. It means the >>>> patch does not give any difference comparing with a current >>>> behavior; >>>> >>>> 2. The global vmap_area_lock, vmap_area_root are removed as there >>>> is no need in it anymore. The vmap_area_list is still kept and >>>> is _empty_. It is exported for a kexec only; >>> >>> I haven't taken a test, while accessing all nodes' busy tree to get >>> va of the lowest address could severely impact kcore reading efficiency >>> on system with many vmap nodes. People doing live debugging via >>> /proc/kcore will get a little surprise. >>> >>> >>> Empty vmap_area_list will break makedumpfile utility, Crash utility >>> could be impactd too. I checked makedumpfile code, it relys on >>> vmap_area_list to deduce the vmalloc_start value. >>> >> It is left part and i hope i fix it in v3. The problem here is >> we can not give an opportunity to access to vmap internals from >> outside. This is just not correct, i.e. you are not allowed to >> access the list directly. > > Right. Thanks for the fix in v3, that is a relief of makedumpfile and > crash. > > Hi Kazu, > > Meanwhile, I am thinking if we should evaluate the necessity of > vmap_area_list in makedumpfile and Crash. In makedumpfile, we just use > vmap_area_list to deduce VMALLOC_START. Wondering if we can export > VMALLOC_START directly. Surely, the lowest va->va_start in vmap_area_list > is a tighter low boundary of vmalloc area and can reduce unnecessary > scanning below the lowest va. Not sure if this is the reason people > decided to export vmap_area_list. The kernel commit acd99dbf5402 introduced the original vmlist entry to vmcoreinfo, but there is no information about why it did not export VMALLOC_START directly. If VMALLOC_START is exported directly to vmcoreinfo, I think it would be enough for makedumpfile. Thanks, Kazu _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec