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 035C4C46CA0 for ; Mon, 4 Dec 2023 12:39:48 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 6E0636B02C4; Mon, 4 Dec 2023 07:39:48 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 690916B02C6; Mon, 4 Dec 2023 07:39:48 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 55A956B02C7; Mon, 4 Dec 2023 07:39:48 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 4593C6B02C4 for ; Mon, 4 Dec 2023 07:39:48 -0500 (EST) Received: from smtpin08.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id 25D8AA020C for ; Mon, 4 Dec 2023 12:39:48 +0000 (UTC) X-FDA: 81529092456.08.05BB66F Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by imf04.hostedemail.com (Postfix) with ESMTP id 4F0404001A for ; Mon, 4 Dec 2023 12:39:46 +0000 (UTC) Authentication-Results: imf04.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf04.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1701693586; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+5b8MBu6rfJuWDzcAfvQbPo0RTOjpJ87Cty6pHQRk6Y=; b=bdtCn/EzR46/vFLdEbQ2lltAipqrDB6lwmWW35OdtjOkLZ1X/PFMQpKZPNZJ43bFysZwaH 2AfDDGomt6p6/0CSZCl4x8sulI9jJGWCM/YezaK4zr/sRQVZ+EmzM6cdJ1zg7bPIsQBFST IwJKkfMZEQtezASjE4xOBKH4WmbqwaM= ARC-Authentication-Results: i=1; imf04.hostedemail.com; dkim=none; dmarc=pass (policy=none) header.from=arm.com; spf=pass (imf04.hostedemail.com: domain of ryan.roberts@arm.com designates 217.140.110.172 as permitted sender) smtp.mailfrom=ryan.roberts@arm.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1701693586; a=rsa-sha256; cv=none; b=gki6Zc5yD+VXLthYvSKeg22I6mZIyElJGIn8N/hkTdcOIS3IrblWIxATUBF1gFAlZUvQOo 8qwEjfQccYXMOVoIyuo3BFkJXkqXjv1IfjygBBsxEMlYGvOIj+X7eMgZS4luAMk6s9aJo0 Ra0ioJLre2npG/m1Aa5/ViCkd8XtoRM= Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A917C1424; Mon, 4 Dec 2023 04:40:32 -0800 (PST) Received: from [10.57.73.130] (unknown [10.57.73.130]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id EA8AC3F5A1; Mon, 4 Dec 2023 04:39:42 -0800 (PST) Message-ID: <52b042b9-ec95-4db0-b38a-f7f1cea0b90c@arm.com> Date: Mon, 4 Dec 2023 12:39:41 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1 4/4] mm/mmu_gather: Store and process pages in contig ranges Content-Language: en-GB To: David Hildenbrand , Zi Yan , Matthew Wilcox Cc: Will Deacon , "Aneesh Kumar K.V" , Andrew Morton , Nick Piggin , Peter Zijlstra , Christian Borntraeger , Sven Schnelle , Arnd Bergmann , Yu Zhao , "Kirill A. Shutemov" , Yin Fengwei , Yang Shi , "Huang, Ying" , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20230810103332.3062143-1-ryan.roberts@arm.com> <20230810103332.3062143-5-ryan.roberts@arm.com> <800937DA-BAD0-4C60-B155-AECCA21E955E@nvidia.com> <1a0f5cb8-421c-4f28-a986-f3c381406e81@arm.com> <90EC4C0D-0254-4B93-AFD5-3C09580A77DE@nvidia.com> <6dd6164a-1dd5-46e7-bcf7-b62ff5c6e8ec@arm.com> <890f4455-bf1b-437b-a355-7895e4dd3085@redhat.com> From: Ryan Roberts In-Reply-To: <890f4455-bf1b-437b-a355-7895e4dd3085@redhat.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: m6h3cg8a361mzumca7k6qb9sh6hsecpa X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 4F0404001A X-HE-Tag: 1701693586-804379 X-HE-Meta: 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 hotSQ67X EFGLT05OkvcG1QD6/XezmxlBzlWT5BQM5NBzrtqfBbqAB9XbwRZSU7c2hskET7gbe0sl4EVxpdlnYwm8LHEJF83HvMVF3KoRtCZFKx6Yz/3tjEnS7A9tt8fjEHvI56xXQ3EXvPIVAWExqTARFcGkw34chofFOoc6Aps9UKMv9j/3STz057O7Vwqpcp5qLY9vdjvEw 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: List-Subscribe: List-Unsubscribe: On 04/12/2023 12:28, David Hildenbrand wrote: > On 04.12.23 13:26, Ryan Roberts wrote: >>>>> >>>>> Also, struct page (memmap) might not be always contiguous, using struct page >>>>> points to represent folio range might not give the result you want. >>>>> See nth_page() and folio_page_idx() in include/linux/mm.h. >>>> >>>> Is that true for pages within the same folio too? Or are all pages in a folio >>>> guarranteed contiguous? Perhaps I'm better off using pfn? >>> >>> folio_page_idx() says not all pages in a folio is guaranteed to be contiguous. >>> PFN might be a better choice. >> >> Hi Zi, Matthew, >> >> Zi made this comment a couple of months back that it is incorrect to assume that >> `struct page`s within a folio are (virtually) contiguous. I'm not sure if that's >> really the case though? I see other sites in the source that do page++ when >> iterating over a folio. e.g. smaps_account(), splice_folio_into_pipe(), >> __collapse_huge_page_copy(), etc. >> >> Any chance someone could explain the rules? > > With the vmemmap, they are contiguous. Without a vmemmap, but with sparsemem, we > might end up allocating one memmap chunk per memory section (e.g., 128 MiB). > > So, for example, a 1 GiB hugetlb page could cross multiple 128 MiB sections, and > therefore, the memmap might not be virtually consecutive. OK, is a "memory section" always 128M or is it variable? If fixed, does that mean that it's impossible for a THP to cross section boundaries? (because a THP is always smaller than a section?) Trying to figure out why my original usage in this series was wrong, but presumably the other places that I mentioned are safe. > >