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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 0D5D7C982DA for ; Mon, 21 Sep 2026 03:44:27 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [127.0.0.1]) by lists.ozlabs.org (Postfix) with ESMTP id 4hp8HG23TGz2yDc; Mon, 21 Sep 2026 13:44:26 +1000 (AEST) Authentication-Results: lists.ozlabs.org; arc=none smtp.remote-ip=95.215.58.87 ARC-Seal: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1789962266; cv=none; b=YDkwamMHvFO43pksduy9LMAMCEGsLdHHU5ATO6tQDQwNx8Nkar7qWe9ghAN+ZvNILl5+qpQuR92tH6Px9U3qr2jcFDtIF05HJ3M4FtX6sUD9hfnMAjUakm/fi/+M2KweSd95wi24mAaqgoDir19OrnCN1F9/ePyrpjDZaHbmUgbxauwxBit1jnoAU6G7XMtwIYAD5qDYwdn88xDXccdOWhJyxqFkAZxs92SS4xNZULIxNIId+LAz4NtkTsGgIRvBv5My0UvuvAKh4FvqPSVA4mvpi28cVWte4HLFo0Jr4/jea2ohokxf1Jr9k0W3VAzjwekkoQBxtJ5oCve09Kebjg== ARC-Message-Signature: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1789962266; c=relaxed/relaxed; bh=obiZyFjcOobmTwuln0nMYhDvmRZvXT8/bzvIQjQRQIw=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=lPdGjkcLRzPvifKTDWT3/AkuuLGYqLY1HQTnwtOTmo98phSe4EjYJcZoGCn/5SznrVS35L2elYRh61X5ECrdfKq5a08/lckbW778gV4AajXcGykaj964B+ZxvdKWskR8VYj+NC5hGxDbZYZOu14s0CS+0Qf2DhNiE4A66ai5MMuQUW+kiVj9mwpBjVmMcuIg2rSXupTve9SbXyaPyf0r/g+tJKabTxPRhJ2So+g6BelvcNc7X1VVSBSCLOiqxU2udZ5ID6OWakzvoChnBiRgoQGBDQxfNbpR4dUR9f+OUhXtKljt6KZ+us0s6zRzLjxOHQj7aG8WPS5eY5FPHBGJeQ== ARC-Authentication-Results: i=1; lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=linux.dev; dkim=pass (1024-bit key; unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=q6i3Cc4v; dkim-atps=neutral; spf=pass (client-ip=95.215.58.87; helo=mta1.migadu.com; envelope-from=qi.zheng@linux.dev; receiver=lists.ozlabs.org) smtp.mailfrom=linux.dev Authentication-Results: lists.ozlabs.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: lists.ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=linux.dev header.i=@linux.dev header.a=rsa-sha256 header.s=key1 header.b=q6i3Cc4v; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linux.dev (client-ip=95.215.58.87; helo=mta1.migadu.com; envelope-from=qi.zheng@linux.dev; receiver=lists.ozlabs.org) Received: from mta1.migadu.com (out-87.mta1.migadu.com [95.215.58.87]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange x25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4hp8HB6HgQz2xdb for ; Mon, 21 Sep 2026 13:44:21 +1000 (AEST) X-Envelope-To: linuxppc-dev@lists.ozlabs.org DKIM-Signature: a=rsa-sha256; bh=OGERyTp5CrbGXz3u1lwBm+Mkoof0KEPSvGD6/69fiBc=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1789962241; v=1; x=1790567041; b=q6i3Cc4vPqW2HACNC1Kbcz5AWkNrBAYd+5bKQYabHMNoOlMMuY3LgSJDfb1uNhWzk0yXNWQ/ H6nBlVUvtNQacO2ypx/6s3g+F0Qqoq+o8ycUPanwPWEII6LLiBx6wFzMsVCccjETiUbB0bUqndW gxfcR9gm2LW9kj92Cy41XQnA= X-Envelope-To: linuxppc-dev@lists.ozlabs.org Received: by smtp.migadu.com with ESMTPS id f06bd7d5875bb714; Mon, 21 Sep 2026 03:44:01 +0000 X-Mizu-Trace-ID: f06bd7d5875bb714 X-Migadu-Flow: FLOW_OUT Message-ID: <95d326cb-ebb4-492c-9062-5d373609e18b@linux.dev> Date: Mon, 21 Sep 2026 11:43:51 +0800 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/6] mm/sparse-vmemmap: drop VMEMMAP_POPULATE_DAX To: Muchun Song Cc: Muchun Song , Madhavan Srinivasan , Mike Rapoport , Andrew Morton , David Hildenbrand , Michael Ellerman , Nicholas Piggin , Christophe Leroy , Lorenzo Stoakes , "Liam R . Howlett" , Vlastimil Babka , Suren Baghdasaryan , Michal Hocko , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20260913083734.86802-1-songmuchun@bytedance.com> <20260913083734.86802-2-songmuchun@bytedance.com> <186ee2ba-daf3-4120-a3e3-101cac1ff5a1@linux.dev> <4AA6C66B-0FD8-49F3-8447-959A3E438FC2@linux.dev> From: Qi Zheng In-Reply-To: <4AA6C66B-0FD8-49F3-8447-959A3E438FC2@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/19/26 10:07 PM, Muchun Song wrote: > > >> On Sep 19, 2026, at 22:01, Qi Zheng wrote: >> On 9/13/26 4:37 PM, Muchun Song wrote: >>> VMEMMAP_POPULATE_DAX currently distinguishes DAX vmemmap population in two >>> places: it keeps allocations on the normal path and takes a reference when >>> a backing page is supplied for reuse. >>> After Device DAX switched to the common per-zone shared tail page, both >>> conditions can be determined locally. DAX supplies ptpfn for every shared >>> tail mapping and requests an allocation only for compound head mappings, >>> whose PFNs are not optimizable. Therefore, vmemmap_optimizable_pfn() alone >>> selects the correct allocation path. >>> When ptpfn is supplied, the caller is reusing an existing backing page. >>> Once the slab allocator is available, take a reference for each reused >> >> Does the availability of slab mean the buddy allocator is already being >> used? Could there be a window where the buddy allocator is functional >> but slab hasn't become available yet? > > Yes, because the slab allocator is based on buddy allocator. But I want to know > what's your concern here? The goal here is to check if the buddy allocator is ready, but the code actually checks for slab. I'm concerned there could be a gap between these two: buddy is ready <-- gap --> slab is ready Thanks, Qi