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]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E13D2C982DE for ; Mon, 21 Sep 2026 03:49:48 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id CFFDB6B00DB; Sun, 20 Sep 2026 23:49:47 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CB1226B00E3; Sun, 20 Sep 2026 23:49:47 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B9FBA6B00E4; Sun, 20 Sep 2026 23:49:47 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0011.hostedemail.com [216.40.44.11]) by kanga.kvack.org (Postfix) with ESMTP id 8AC2E6B00DB for ; Sun, 20 Sep 2026 23:49:47 -0400 (EDT) Received: from smtpin23.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay05.hostedemail.com (Postfix) with ESMTP id E6EF340555 for ; Mon, 21 Sep 2026 03:49:46 +0000 (UTC) X-FDA: 85236390372.23.E6FCC29 Received: from mta1.migadu.com (out-239.mta1.migadu.com [95.215.58.239]) by imf24.hostedemail.com (Postfix) with ESMTP id 1E8EF180004 for ; Mon, 21 Sep 2026 03:49:42 +0000 (UTC) Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=R3djp9Lp; spf=pass (imf24.hostedemail.com: domain of muchun.song@linux.dev designates 95.215.58.239 as permitted sender) smtp.mailfrom=muchun.song@linux.dev; dmarc=pass (policy=none) header.from=linux.dev ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1789962585; 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:dkim-signature; bh=28SAODsjBVAdEFNL/DREIySi6dVovlUoxUjNe7E0v7k=; b=opClwJEwO0XeCbytSn0qURlhLghs6rF+ps0zz1JvqbYzkew/6JyhhrsLM8xtBEKGVKDe49 83YTVCQIEfodiGT2iheYujnltrEq6i213yDLKVJjmne3cNLIASKd1CExwN8Vmdzi/IN6jP P1861dvNmLYxChHbNsy32l/vkKmOv9Q= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1789962585; b=QaURoSRYbEKXol1lVeZ1NxAI8CiEq32pLjLxAizUR/uqUb1Q81Aul4Yj13/89TVSr+nOvE alfs7xxvI3Wwq0syIzPHcgr2cunAZOFSDsoRQ71reXq6IwGrCZVQmhn5BgnAFkMu8Syh1e dJO8k8RKjeMHjNsFIRe38rXwkNECEoo= ARC-Authentication-Results: i=1; imf24.hostedemail.com; dkim=pass header.d=linux.dev header.s=key1 header.b=R3djp9Lp; spf=pass (imf24.hostedemail.com: domain of muchun.song@linux.dev designates 95.215.58.239 as permitted sender) smtp.mailfrom=muchun.song@linux.dev; dmarc=pass (policy=none) header.from=linux.dev X-Envelope-To: linux-mm@kvack.org DKIM-Signature: a=rsa-sha256; bh=28SAODsjBVAdEFNL/DREIySi6dVovlUoxUjNe7E0v7k=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1789962580; v=1; x=1790567380; b=R3djp9Lp6q7p1WQW44p6wZoyKGyJN0bqYAZSySR1ojICUXRB2S1cozr2bAwNFJhz4iN3zIf3 vX3oEkH4Yx7LZ1g7RMkzlXW5dBE+cBtq376DVzzzUpqmBWzUsJDJd7Gz5LwiPbIzWxTMLoDl2PU kEmUhQUTmSbSfTviXpL/KLeE= X-Envelope-To: linux-mm@kvack.org Received: by mta10.migadu.com with ESMTPS id e91057e5e69ad459; Mon, 21 Sep 2026 03:49:39 +0000 X-Mizu-Trace-ID: e91057e5e69ad459 X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Mac OS X Mail 16.0 \(3864.700.51.1.1\)) Subject: Re: [PATCH 1/6] mm/sparse-vmemmap: drop VMEMMAP_POPULATE_DAX From: Muchun Song In-Reply-To: <95d326cb-ebb4-492c-9062-5d373609e18b@linux.dev> Date: Mon, 21 Sep 2026 11:49:23 +0800 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 Content-Transfer-Encoding: quoted-printable Message-Id: <6479325A-E6FA-45BD-9392-262E71467EDB@linux.dev> 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> <95d326cb-ebb4-492c-9062-5d373609e18b@linux.dev> To: Qi Zheng X-Mailer: Apple Mail (2.3864.700.51.1.1) X-Rspamd-Server: rspam04 X-Rspam-User: X-Stat-Signature: mtt51zg8j6eedkkn93cmh756g8f57b77 X-Rspamd-Queue-Id: 1E8EF180004 X-HE-Tag: 1789962582-165531 X-HE-Meta: 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 HZFHSsc2 Ic3do8cHhjdgPpUpw2D+PYAncoRh4y/5exoRITOKMUsyfQONbSDVXvad9cUnzaa8EV4NtLk4mmlv/RjFDK4Rs1oHlg/EBVlcAeAfMpQWY66RhrdgH/s+9NqFdpsL3dt1FIMdknk5foT/KetD4x8lgWzItK6vlqD4JEf5lXNDizPQw3zHujCEXQ/eaxRdzojsZFJNtS40JsokodTP8DUX+Rg7mD0cryxLiDLmRjxdxmDp9/0uYu0Ze66z8x1KEqG2AS69o/uSyBCRZ44DhBJ9V1emHfO2u+vaj2WrFhutqgbTBMNLdDSyU7dxIiQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > On Sep 21, 2026, at 11:43, Qi Zheng wrote: > 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 >>>=20 >>> 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? >=20 > The goal here is to check if the buddy allocator is ready, but the = code > actually checks for slab. >=20 > I'm concerned there could be a gap between these two: >=20 > buddy is ready <-- gap --> slab is ready There is no vmemmap population during the gap. We don't need to concern = the gap. Thanks. >=20 > Thanks, > Qi >=20 >=20