From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta1.migadu.com (out-236.mta1.migadu.com [95.215.58.236]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 3B735318ED7 for ; Mon, 21 Sep 2026 03:49:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.236 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789962584; cv=none; b=GXYqsjRLCYOjobPpVe4O8wFlNfYt3rkk8fZwOo7Y433J//YyZo/h/Tlp4VxW26MEBWxMYE1tPJDbJ5CnNeQnKVkHjXTCAIsmA+lqxXC+ZdPgmgCyDXw2POWyPPsJdsShQC/oZeLVdp3fUEMGgVoJ6qP3TjNfMY7oVxwrbJnWkDo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789962584; c=relaxed/simple; bh=28SAODsjBVAdEFNL/DREIySi6dVovlUoxUjNe7E0v7k=; h=Content-Type:Mime-Version:Subject:From:In-Reply-To:Date:Cc: Message-Id:References:To; b=jns1viTEMPgcg3K2pN6V6KO0HoyvDzKofF2wzzlAxdTe8YYwHJVVpOe8xiDo8oZ00DDCPSq0e6Rlmp7cKIHjq6qQLx28qd0V4eC3qmd8moRW3WNiXYVSWOI7c1Z78xNDF7JenESigKpoLdoRjrRaslDE+7/CZF5+ae/HXJyNKEs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=R3djp9Lp; arc=none smtp.client-ip=95.215.58.236 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="R3djp9Lp" X-Envelope-To: linux-kernel@vger.kernel.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-kernel@vger.kernel.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 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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) > 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