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 E41B1C982D7 for ; Sat, 19 Sep 2026 14:08:02 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [127.0.0.1]) by lists.ozlabs.org (Postfix) with ESMTP id 4hnBCj0pHHz2xYg; Sun, 20 Sep 2026 00:08:01 +1000 (AEST) Authentication-Results: lists.ozlabs.org; arc=none smtp.remote-ip="2001:41d0:1004:224b::c6" ARC-Seal: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1789826881; cv=none; b=R9aXB3fF+NdMjNpQBYtA0zHJzhsv+NPfBPS98nEaLXOXFQJ07x0cqLlJviTOxgDuRf8XYh/RvPhQYS6TRUkH2wl+KA5V5C/GEVjaLgiqCWcQCJJkaW7THY46wI/72PmiOCOcKb0MmBk9x3zAtmI/Dj1m8fyDZDHamo/qKDn0cx6r7pc6GRhf8ltZWtFvNHs86wGWJTKyuGguRwVWNsDVDqt8vwYIyPbqZIV5O7za88V06lczBzRCgerGOilMU1N18c6nPkevIMZZ3ZAiWx8WpicX19D1JZ7QZUmE5QtJWNJX+g3qapcLPA9cwB+u/VnrYCQONs/C9/XoCAfuFZwXkA== ARC-Message-Signature: i=1; a=rsa-sha256; d=lists.ozlabs.org; s=201707; t=1789826881; c=relaxed/relaxed; bh=1RJtSmGkDzOhRF7zExD6eG4nMnJW5Es9Ic7XyY94Oj4=; h=Content-Type:Mime-Version:Subject:From:In-Reply-To:Date:Cc: Message-Id:References:To; b=mwCsincrIbR9UaY/u/6witEyfDlJJJPaClsgfBVW8a1vbjxSUQ4CagiEYvgsI6J2gSREytTK9gBJlJqtbSnJPoR97O01+Pl9ull/zYJSxoYHKhix0YkhMlKEdgsl7K4HvDUfodIkhiKyoi1yl1c966h2gi4XcKxgoDjc/GMrWgg5la5JqY43ChNzbQRHofzl0EVupClCIm3HHQILTJBJVvieSrWq4ZeqSHlixdjj+WReP8TznIEpHUZEj6aEY9ESbBnB1xKD8Jk4wm9bl+fsOuAC/6bbLM86qApCL14kPb1Q7XOeiWN9JhMlB83OtRZObenXx37FagxFTwmW23MCBA== 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=mqt6FUuX; dkim-atps=neutral; spf=pass (client-ip=2001:41d0:1004:224b::c6; helo=mta0.migadu.com; envelope-from=muchun.song@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=mqt6FUuX; dkim-atps=neutral Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=linux.dev (client-ip=2001:41d0:1004:224b::c6; helo=mta0.migadu.com; envelope-from=muchun.song@linux.dev; receiver=lists.ozlabs.org) Received: from mta0.migadu.com (out-198.mta0.migadu.com [IPv6:2001:41d0:1004:224b::c6]) (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 4hnBCg6kdgz2xST for ; Sun, 20 Sep 2026 00:07:58 +1000 (AEST) X-Envelope-To: linuxppc-dev@lists.ozlabs.org DKIM-Signature: a=rsa-sha256; bh=1RJtSmGkDzOhRF7zExD6eG4nMnJW5Es9Ic7XyY94Oj4=; c=simple/simple; d=linux.dev; h=from:to:subject:date:message-id:mime-version:content-type; s=key1; t=1789826860; v=1; x=1790431660; b=mqt6FUuXMFr5TEmLd/Q/Yc7UnGrkFFt7cnv558YaEsU6Vh8n7PyA8OR+ru3pS1o5JvD957Yk +b3PDUY6awRtFAZWYIo+vVXFm5eURkdXn6ow9TQg96V92kPVGoWdAUTtvB9B3qysIv8E+t14uye rg662j5uUpj680cmtR7g5Ql4= X-Envelope-To: linuxppc-dev@lists.ozlabs.org Received: by mta11.migadu.com with ESMTPS id b0b09ee52edac098; Sat, 19 Sep 2026 14:07:40 +0000 X-Mizu-Trace-ID: b0b09ee52edac098 X-Migadu-Flow: FLOW_OUT Content-Type: text/plain; charset=us-ascii 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 (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: <186ee2ba-daf3-4120-a3e3-101cac1ff5a1@linux.dev> Date: Sat, 19 Sep 2026 22:07:19 +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: <4AA6C66B-0FD8-49F3-8447-959A3E438FC2@linux.dev> References: <20260913083734.86802-1-songmuchun@bytedance.com> <20260913083734.86802-2-songmuchun@bytedance.com> <186ee2ba-daf3-4120-a3e3-101cac1ff5a1@linux.dev> To: Qi Zheng X-Mailer: Apple Mail (2.3864.700.51.1.1) > 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?=