From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6C128C433F5 for ; Mon, 27 Dec 2021 15:56:25 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 7ABF96B0072; Mon, 27 Dec 2021 10:56:24 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 734356B0073; Mon, 27 Dec 2021 10:56:24 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 5AE306B0074; Mon, 27 Dec 2021 10:56:24 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0203.hostedemail.com [216.40.44.203]) by kanga.kvack.org (Postfix) with ESMTP id 480166B0072 for ; Mon, 27 Dec 2021 10:56:24 -0500 (EST) Received: from smtpin13.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id BC4F1805C9 for ; Mon, 27 Dec 2021 15:56:23 +0000 (UTC) X-FDA: 78964026246.13.0F9008B Received: from mga18.intel.com (mga18.intel.com [134.134.136.126]) by imf15.hostedemail.com (Postfix) with ESMTP id C99D0A000F for ; Mon, 27 Dec 2021 15:56:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1640620582; x=1672156582; h=subject:to:cc:references:from:message-id:date: mime-version:in-reply-to:content-transfer-encoding; bh=Qopi0GCbZb8D3tqnGHATwO1hv9M0cdIa+FRZv6opEto=; b=NWzgkBEOc1KR0mx0OIEI0IaIpzxgHR/cZwMt4apX5p0qU4H1ZdO4oaUR VfDTNUY79954cG6JeCCYTkRmR29PCQ82QJCxYozcNa1DbJhTgmizZbyrB MpqyvToNEJDLF2jYGSwq9AJ61Q4fRchUOJmGvNvOobful24Y8wUo4ZtGb SaMhto2wcX9WGPAwhyAmudhn/1toS8pQl6C8ID/XrTkltqVXquw600Pn+ lCF+8dlsNjciXJ/muJYjvs1KkTYHAllJ2GhwP3DnWeFIrswjjYnaX0IAn U/y+KWA0d/e/NWHe/Mr6BlMUdaDrfGyuvvs4AXPXPcYNcP2wnBOW+1Ufv Q==; X-IronPort-AV: E=McAfee;i="6200,9189,10209"; a="228059243" X-IronPort-AV: E=Sophos;i="5.88,239,1635231600"; d="scan'208";a="228059243" Received: from orsmga002.jf.intel.com ([10.7.209.21]) by orsmga106.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Dec 2021 07:56:17 -0800 X-IronPort-AV: E=Sophos;i="5.88,239,1635231600"; d="scan'208";a="486053937" Received: from dannysua-mobl2.amr.corp.intel.com (HELO [10.212.232.47]) ([10.212.232.47]) by orsmga002-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 27 Dec 2021 07:56:16 -0800 Subject: Re: [PATCH v2 3/3] x86: Support huge vmalloc mappings To: Kefeng Wang , Jonathan Corbet , Andrew Morton , linuxppc-dev@lists.ozlabs.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org Cc: Nicholas Piggin , Catalin Marinas , Will Deacon , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Michael Ellerman , Benjamin Herrenschmidt , Paul Mackerras , Christophe Leroy , Matthew Wilcox References: <20211227145903.187152-1-wangkefeng.wang@huawei.com> <20211227145903.187152-4-wangkefeng.wang@huawei.com> From: Dave Hansen Message-ID: <70ff58bc-3a92-55c2-2da8-c5877af72e44@intel.com> Date: Mon, 27 Dec 2021 07:56:14 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 In-Reply-To: <20211227145903.187152-4-wangkefeng.wang@huawei.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: C99D0A000F X-Stat-Signature: 44wnbzn4n9pztoj9ugipxnbkw536b3ts Authentication-Results: imf15.hostedemail.com; dkim=pass header.d=intel.com header.s=Intel header.b=NWzgkBEO; dmarc=pass (policy=none) header.from=intel.com; spf=none (imf15.hostedemail.com: domain of dave.hansen@intel.com has no SPF policy when checking 134.134.136.126) smtp.mailfrom=dave.hansen@intel.com X-Rspamd-Server: rspam02 X-HE-Tag: 1640620571-757068 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 12/27/21 6:59 AM, Kefeng Wang wrote: > This patch select HAVE_ARCH_HUGE_VMALLOC to let X86_64 and X86_PAE > support huge vmalloc mappings. In general, this seems interesting and the diff is simple. But, I don't see _any_ x86-specific data. I think the bare minimum here would be a few kernel compiles and some 'perf stat' data for some TLB events. > diff --git a/arch/x86/kernel/module.c b/arch/x86/kernel/module.c > index 95fa745e310a..6bf5cb7d876a 100644 > --- a/arch/x86/kernel/module.c > +++ b/arch/x86/kernel/module.c > @@ -75,8 +75,8 @@ void *module_alloc(unsigned long size) > > p = __vmalloc_node_range(size, MODULE_ALIGN, > MODULES_VADDR + get_module_load_offset(), > - MODULES_END, gfp_mask, > - PAGE_KERNEL, VM_DEFER_KMEMLEAK, NUMA_NO_NODE, > + MODULES_END, gfp_mask, PAGE_KERNEL, > + VM_DEFER_KMEMLEAK | VM_NO_HUGE_VMAP, NUMA_NO_NODE, > __builtin_return_address(0)); > if (p && (kasan_module_alloc(p, size, gfp_mask) < 0)) { > vfree(p); To figure out what's going on in this hunk, I had to look at the cover letter (which I wasn't cc'd on). That's not great and it means that somebody who stumbles upon this in the code is going to have a really hard time figuring out what is going on. Cover letters don't make it into git history. This desperately needs a comment and some changelog material in *this* patch. But, even the description from the cover letter is sparse: > There are some disadvantages about this feature[2], one of the main > concerns is the possible memory fragmentation/waste in some scenarios, > also archs must ensure that any arch specific vmalloc allocations that > require PAGE_SIZE mappings(eg, module alloc with STRICT_MODULE_RWX) > use the VM_NO_HUGE_VMAP flag to inhibit larger mappings. That just says that x86 *needs* PAGE_SIZE allocations. But, what happens if VM_NO_HUGE_VMAP is not passed (like it was in v1)? Will the subsequent permission changes just fragment the 2M mapping?