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 X-Spam-Level: X-Spam-Status: No, score=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DD3A9C433B4 for ; Mon, 5 Apr 2021 21:02:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A5D9B6139F for ; Mon, 5 Apr 2021 21:02:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241194AbhDEVCH (ORCPT ); Mon, 5 Apr 2021 17:02:07 -0400 Received: from mga07.intel.com ([134.134.136.100]:34793 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237300AbhDEVCG (ORCPT ); Mon, 5 Apr 2021 17:02:06 -0400 IronPort-SDR: soEgZbHxwJsLIFFMwIjwWc59IL8dhnuV9uxzq6P/CZBYDhyys2dM2d46Fy7mSRqPYkfY0pZYT3 hWZ+gvpiPxQA== X-IronPort-AV: E=McAfee;i="6000,8403,9945"; a="256908590" X-IronPort-AV: E=Sophos;i="5.81,307,1610438400"; d="scan'208";a="256908590" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Apr 2021 14:01:59 -0700 IronPort-SDR: o+gAVIFmH11CT3k4mPTCaWOFMEuoUXlD5TU/3DPISumNTD1c1CmxSGRVSAbqfS6FH5befZEJQf d/9JSzvr5PYA== X-IronPort-AV: E=Sophos;i="5.81,307,1610438400"; d="scan'208";a="414446416" Received: from wenhuali-mobl1.amr.corp.intel.com (HELO [10.254.184.105]) ([10.254.184.105]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 05 Apr 2021 14:01:58 -0700 Subject: Re: [RFC 2/3] vmalloc: Support grouped page allocations To: Rick Edgecombe , akpm@linux-foundation.org, linux-mm@kvack.org, bpf@vger.kernel.org, dave.hansen@linux.intel.com, peterz@infradead.org, luto@kernel.org, jeyu@kernel.org Cc: linux-kernel@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, hch@infradead.org, x86@kernel.org References: <20210405203711.1095940-1-rick.p.edgecombe@intel.com> <20210405203711.1095940-3-rick.p.edgecombe@intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210405203711.1095940-3-rick.p.edgecombe@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On 4/5/21 1:37 PM, Rick Edgecombe wrote: > +static void __dispose_pages(struct list_head *head) > +{ > + struct list_head *cur, *next; > + > + list_for_each_safe(cur, next, head) { > + list_del(cur); > + > + /* The list head is stored at the start of the page */ > + free_page((unsigned long)cur); > + } > +} This is interesting. While the page is in the allocator, you're using the page contents themselves to store the list_head. It took me a minute to figure out what you were doing here because: "start of the page" is a bit ambiguous. It could mean: * the first 16 bytes in 'struct page' or * the first 16 bytes in the page itself, aka *page_address(page) The fact that this doesn't work on higmem systems makes this an OK thing to do, but it is a bit weird. It's also doubly susceptible to bugs where there's a page_to_virt() or virt_to_page() screwup. I was *hoping* there was still sufficient space in 'struct page' for this second list_head in addition to page->lru. I think there *should* be. That would at least make this allocator a bit more "normal" in not caring about page contents while the page is free in the allocator. If you were able to do that you could do things like kmemcheck or page alloc debugging while the page is in the allocator. Anyway, I think I'd prefer that you *try* to use 'struct page' alone. But, if that doesn't work out, please comment the snot out of this thing because it _is_ weird.