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Wed, 15 Sep 2021 08:21:53 +0000 Received: from VI1PR04MB5600.eurprd04.prod.outlook.com ([fe80::4d37:ec64:4e90:b16b]) by VI1PR04MB5600.eurprd04.prod.outlook.com ([fe80::4d37:ec64:4e90:b16b%7]) with mapi id 15.20.4523.014; Wed, 15 Sep 2021 08:21:53 +0000 Subject: Re: [PATCH 04/12] swiotlb-xen: ensure to issue well-formed XENMEM_exchange requests To: Stefano Stabellini Cc: Juergen Gross , Boris Ostrovsky , lkml , "xen-devel@lists.xenproject.org" References: <588b3e6d-2682-160c-468e-44ca4867a570@suse.com> <397bf325-f81e-e104-6142-e8c9c4955475@suse.com> <9819a6e9-93d5-e62a-7b4a-ffc2ecd996dc@suse.com> From: Jan Beulich Message-ID: Date: Wed, 15 Sep 2021 10:21:51 +0200 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: AM8P251CA0025.EURP251.PROD.OUTLOOK.COM (2603:10a6:20b:21b::30) To VI1PR04MB5600.eurprd04.prod.outlook.com (2603:10a6:803:e7::16) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [10.156.60.236] (37.24.206.209) by AM8P251CA0025.EURP251.PROD.OUTLOOK.COM (2603:10a6:20b:21b::30) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4523.14 via Frontend Transport; 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I don't mind either way but you >>>>>> can go ahead and remove it if you prefer (and it would make the line >>>>>> shorter.) >>>>>> >>>>>> >>>>>>> I further wonder how useful it is to wrap "bytes" in >>>>>>> PAGE_ALIGN(), when it is a multiple of a segment's size anyway (or at >>>>>>> least was supposed to be, prior to "swiotlb-xen: maintain slab count >>>>>>> properly"). >>>>>> >>>>>> This one I would keep, to make sure to print out the same amount passed >>>>>> to memblock_alloc. >>>>> >>>>> Oh - if I was to drop it from the printk(), I would have been meaning to >>>>> also drop it there. If it's useless, then it's useless everywhere. >>>> >>>> That's fine too >>> >>> Thanks, I'll see about dropping that then. >>> >>> Another Arm-related question has occurred to me: Do you actually >>> mind the higher-than-necessary alignment there? If so, a per-arch >>> definition of the needed alignment would need introducing. Maybe >>> that could default to PAGE_SIZE, allowing Arm and alike to get away >>> without explicitly specifying a value ... >> >> Certainly a patch like that could be good. Given that it is only one >> allocation I was assuming that the higher-than-necessary alignment >> wouldn't be a problem worth addressing (and I cannot completely rule out >> that one day we might have to use XENMEM_exchange on ARM too). > > Also this code is currently #ifdef CONFIG_X86 Oh, good point. When writing the patch I did take this into consideration, but I had managed to forget that aspect in the meantime. No adjustment to this effect needed then. Jan