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Mon, 27 Nov 2023 01:06:06 +0000 Received: from SN6PR02MB4157.namprd02.prod.outlook.com ([fe80::54e5:928f:135c:6190]) by SN6PR02MB4157.namprd02.prod.outlook.com ([fe80::54e5:928f:135c:6190%7]) with mapi id 15.20.7025.022; Mon, 27 Nov 2023 01:06:06 +0000 From: Michael Kelley To: Christoph Hellwig CC: "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "dave.hansen@linux.intel.com" , "x86@kernel.org" , "hpa@zytor.com" , "kirill.shutemov@linux.intel.com" , "kys@microsoft.com" , "haiyangz@microsoft.com" , "wei.liu@kernel.org" , "decui@microsoft.com" , "luto@kernel.org" , "peterz@infradead.org" , "akpm@linux-foundation.org" , "urezki@gmail.com" , "lstoakes@gmail.com" , "thomas.lendacky@amd.com" , "ardb@kernel.org" , "jroedel@suse.de" , "seanjc@google.com" , "rick.p.edgecombe@intel.com" , "sathyanarayanan.kuppuswamy@linux.intel.com" , "linux-kernel@vger.kernel.org" , "linux-coco@lists.linux.dev" , "linux-hyperv@vger.kernel.org" , "linux-mm@kvack.org" Subject: RE: [PATCH v2 3/8] x86/mm: Remove "static" from vmap_pages_range() Thread-Topic: [PATCH v2 3/8] x86/mm: Remove "static" from vmap_pages_range() Thread-Index: AQHaHMCcNHra+kumRUKExlyvEEqwbLCF4AyAgAEpOhCAAHuSgIAF2cCA Date: Mon, 27 Nov 2023 01:06:06 +0000 Message-ID: References: <20231121212016.1154303-1-mhklinux@outlook.com> <20231121212016.1154303-4-mhklinux@outlook.com> In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-tmn: [8sq0PsiZIh4OiZxFtOxeEFKLYajZBv4t] x-ms-publictraffictype: Email x-ms-traffictypediagnostic: SN6PR02MB4157:EE_|DM6PR02MB6859:EE_ x-ms-office365-filtering-correlation-id: f9e86026-9ebc-435f-1284-08dbeee508ad x-microsoft-antispam: BCL:0; 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Please try to come = up > > > with a good way to encapsulate your map at a certain address primitiv= e > > > and implement it in vmalloc.c. > > > > To clarify, is your concern narrowly about vmap_pages_range() > > specifically? >=20 > The prime concern is that it took a lot of effort to make > vmap_pages_range static and remove all the abuses. I absolutely > object to undoing that. OK, so I assume that means a new variant of vmap_pages_range(), such as one that always sets the page_shift parameter to PAGE_SIZE, is also disallowed because of the same potential for abuse. So the only way to map a system memory page to a vmalloc vaddr is via vmap() or some vmap() variant, which always creates a new vmalloc area via get_vm_area(). I've done the perf measurements, and that approach won't work for this use case. Independent of the alignment requirements, the churn in creating and removing a lot of vmalloc areas has too much perf impact. The use case needs to create a single vmalloc area, and then repeatedly map/unmap a page in that existing area. I'll have to handle the top-level problem in this patch set in a completely different way. Michael