From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mta0.migadu.com (out-64.mta0.migadu.com [91.218.175.64]) (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 4E91378C9C for ; Sat, 19 Sep 2026 14:07:41 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=91.218.175.64 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789826864; cv=none; b=OnXvkOttQtVmCvjvIAip2vbFGbVEWRdrO6LeoXFSf2leSTWOU6DlnsHIIy0cWCXzoLZu8NT7Q2ptIyBuC8q1imDD38WlPbamKPOQE1H9kosWgAZLqoIhFzS/nEkHcOZcPnvw/ynN9nt9C7j0959zmlvcgMflvzab8dQdQa+NLpI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789826864; c=relaxed/simple; bh=1RJtSmGkDzOhRF7zExD6eG4nMnJW5Es9Ic7XyY94Oj4=; h=Content-Type:Mime-Version:Subject:From:In-Reply-To:Date:Cc: Message-Id:References:To; b=Rrc7i07crR540GpcpTAKep4+NRQiUqFh+tKO0i8/snkf+eKlyJg8BA4utZeMu5XRZ53udnNXue5y29mvxWRAwBKJk65c9idy7lVbBcAbeUiTvIPzO+wRyZo0roEec0Au4/T9oZ5caXECLEl8AHm328FuVeH5OmahU+L1x5myWec= 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=mqt6FUuX; arc=none smtp.client-ip=91.218.175.64 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="mqt6FUuX" X-Envelope-To: linux-kernel@vger.kernel.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: linux-kernel@vger.kernel.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 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: <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?=