From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2912E339389 for ; Wed, 12 Aug 2026 10:32:28 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786530750; cv=none; b=H90v1tRawFlI7M5joMqpYwaC+xWX6fEGg/UgaQBzxJZJkxAQh91JQINLXx96HC07EF13vZ6QWry8IbmFnkrUQ6mr/vDuDZHhA5niAZKggVDY/pMNu3DfnkcKANM6HwfBx/q3n5lr4aHG4+BahPw1uWpdKyxRyDax1zZwK5EZPBQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786530750; c=relaxed/simple; bh=GAZeX5n5rsK/KHxm6gvUo3lHeShHl0BJJymjNppf3TM=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=j9Gq4vsdlixnkpYMLbT6LK5AOAeG1FJgdtaSEdw9AXZHvJcTjxbyaG6zs2FiVUAJ5uISSjpVyYAcprxSmq5yzEGWxQEnxlowk1fO5ZLITqCcWCMpZeZIkt+SlxJ9PVuung9IZE0TxX38aNN1oEt1bDauQ7eEOBb2PepXrA0pz0c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=HeDSLgDM; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="HeDSLgDM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 011DA1F000E9; Wed, 12 Aug 2026 10:32:26 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786530748; bh=7enFee0jAt08OEyw0dUeqUaEU2QqTLX8gKg/GfUdVQo=; h=From:To:Cc:Subject:In-Reply-To:References:Date; b=HeDSLgDM6lV5H3FjBS7R0fKuLaRZlILJlBAykX+QILIl6u593Cn5+YEZ6cP7bAL/z 1hIIuDEvmhvWJe+sAi4nQNciJis5uxa++bY8vAFlUYXmTa16eLXdK8I90EKszZFt+y 6XOWjBn8PaGLWuYCWt7CgHfGYAeXpNUsCB/NYAY+I2Ein1nwAsySA119VYUb3E406d FipOXlUdZIXF4n4qEfdue4yR74U85S59MD2Ej43NemqcvyFM4raZQTHea4HVJxJ49j hP9S9rigy180grTLHjxasl+WKjERwi+MM51yB3PKYnrUuZqGyRbN5KFTJhRK5KMY+c MQwBYbMgjsw0Q== From: Pratyush Yadav To: Mike Rapoport Cc: Pranjal Shrivastava , Pasha Tatashin , Pratyush Yadav , Alexander Graf , Samiullah Khawaja , David Matlack , kexec@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4 0/2] kho: support preserving high-order non-compound pages In-Reply-To: (Mike Rapoport's message of "Tue, 11 Aug 2026 13:27:04 +0300") References: <20260803113944.3694290-1-praan@google.com> Date: Wed, 12 Aug 2026 12:32:25 +0200 Message-ID: <2vxzv79f39za.fsf@kernel.org> User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain On Tue, Aug 11 2026, Mike Rapoport wrote: > Hi Pranjal, > > On Mon, Aug 03, 2026 at 11:39:41AM +0000, Pranjal Shrivastava wrote: >> Introduction >> ============ >> This series is required for the ongoing effort to preserve DMA allocations >> across KHO [1]. It addresses a fundamental mismatch between the current KHO >> restoration logic and the physical reality of high-order buddy allocations. > > I skimmed through the patches, they look fine to me before the in-depth > review :) > > But we are really close to the merge window, so we'll anyway need to > reiterate after v7.3-rc1. > >> The Problem >> =========== >> The current KHO restore implementation treats all multi-page blocks as >> split pages during restoration. Specifically, kho_restore_pages() >> initializes every 4KB sub-page with a refcount of 1. >> >> However, many kernel subsystems, most notably the DMA allocator (via >> dma_alloc_coherent), frequently return high-order non-compound pages. >> In this state, only the head page carries a refcount of 1, while >> all tail pages have a refcount of 0. > > This hints that these patches could be a part of the DMA preservation > series, unless you expect other users of the new API. > > Generally, we don't merge new APIs without the users and if DMA > preservation is the only user, it's better to fold these two patches there. Makes sense I think. We can review the patches here, but then they can go in with the DMA series. -- Regards, Pratyush Yadav