From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 4AB9D1552FD for ; Thu, 25 Sep 2025 09:19:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758791981; cv=none; b=IZ4up6Ay4/tnFR29eLzz4RdbEVhLp87/1JoghqoXJCCwhiOW4NKu449lQf83FyGTm8jOwzgONqHKEQDD32gLh8cO5nQQqkMoBKtfJ2bI+cXSHd+h/eA5ga6OqXwth4A3GLio5ror1YDPObbzF8iVby7j2nZlpD231TzOPg5CNY0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758791981; c=relaxed/simple; bh=AQqMJQUBDrq9kxPLr/qGEjxf9utS86NJR0MoZy6d1v4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=CfBj1ZYRjYGnhJfpMppMAJXGKziIJCroXT0xXCuXGGakI0kpToZ6lPaA3PD3tvY+LfY24Oqr3ukMQ+f6sggKWYF14f7sifcprxyCXZ3DEWxdqF48t9QdJudmYtcLgMnvbHW09PzCV26i6izc6T/OxOxgToSK2FYUqBkWth4ihgA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=k0RZZ1Rb; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="k0RZZ1Rb" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C96BDC4CEF0; Thu, 25 Sep 2025 09:19:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1758791980; bh=AQqMJQUBDrq9kxPLr/qGEjxf9utS86NJR0MoZy6d1v4=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=k0RZZ1RbKWAAkwlLtYKHcY7S4z/MVWCM50D//MM7NbnU4x0VQ104OQW68HBeAYRYE Gk60I4tro2JMqe3Qjc8LwqFxAq2mJlq+lKwYDTQWUkX3AkNoBii2ZDZfEvqZN3rEM3 A3jYcewOMAlaG7c+WSx11wDrWKMqV5Bcp+7l8t8kM9isRSp+OuRBU+FwhwS9ueFh46 0/QAkKl2M040I2KBKOwHwNMlJg2blEiveia9uQcZQJmWSKPe2WfUhlSKJLGTLszk2K Fb5QnhvksFC9LTB8hhqUzWg6e7ye1m3pyxoM4nRn+bZFFpXmDoPpHtCOVBTNV3MagN yOB/K5Ig541Lg== Date: Thu, 25 Sep 2025 12:19:30 +0300 From: Mike Rapoport To: Jason Miu Cc: Alexander Graf , Andrew Morton , Baoquan He , Changyuan Lyu , David Matlack , David Rientjes , Jason Gunthorpe , Joel Granados , Marcos Paulo de Souza , Mario Limonciello , Pasha Tatashin , Petr Mladek , "Rafael J . Wysocki" , Steven Chen , Yan Zhao , kexec@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC v1 0/4] Make KHO Stateless Message-ID: References: <20250917025019.1585041-1-jasonmiu@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250917025019.1585041-1-jasonmiu@google.com> Hi Jason, On Tue, Sep 16, 2025 at 07:50:15PM -0700, Jason Miu wrote: > This series transitions KHO from an xarray-based metadata tracking > system with serialization to using page table like data structures > that can be passed directly to the next kernel. > > The key motivations for this change are to: > - Eliminate the need for data serialization before kexec. > - Remove the former KHO state machine by deprecating the finalize > and abort states. > - Pass preservation metadata more directly to the next kernel via the FDT. If we pass the preservation metadata directly between the kernels, it means that any change to that data structure will break compatibility between the new and old kernels. With serialization this is less severe because a more recent kernel can relatively easy have backward compatible deserialization. I'm all for removing KHO state machine, but that does not necessarily mean we must remove the serialization of memory persistence metadata? For example, we can do the serialization at kernel_kexec() time and if we want to avoid memory allocations there we might preallocate pages for khoser_mem_chunk's as amount of bitmaps grow. It also would be interesting to see how much time is saved if we remove the serialization. -- Sincerely yours, Mike.