From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932256AbWFMVNS (ORCPT ); Tue, 13 Jun 2006 17:13:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932259AbWFMVNS (ORCPT ); Tue, 13 Jun 2006 17:13:18 -0400 Received: from xenotime.net ([66.160.160.81]:59289 "HELO xenotime.net") by vger.kernel.org with SMTP id S932256AbWFMVNQ (ORCPT ); Tue, 13 Jun 2006 17:13:16 -0400 Date: Tue, 13 Jun 2006 14:16:00 -0700 From: "Randy.Dunlap" To: John Richard Moser Cc: jengelh@linux01.gwdg.de, linux-kernel@vger.kernel.org Subject: Re: Packing data in kernel memory Message-Id: <20060613141600.c736e183.rdunlap@xenotime.net> In-Reply-To: <448F2602.2030402@comcast.net> References: <448F0893.1080706@comcast.net> <20060613133227.1eee4578.rdunlap@xenotime.net> <448F2602.2030402@comcast.net> Organization: YPO4 X-Mailer: Sylpheed version 2.2.5 (GTK+ 2.8.3; x86_64-unknown-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 13 Jun 2006 16:54:26 -0400 John Richard Moser wrote: > Randy.Dunlap wrote: > > On Tue, 13 Jun 2006 22:18:55 +0200 (MEST) Jan Engelhardt wrote: > > > >>> Subject: Packing data in kernel memory > >>> > >> Can't you just use mlock(), if you want to keep it in RAM? > >> > >> Or do you need it in kernel memory, because you need it in the lowmem area? > >> Or for interaction with other kernel code? > >> > >>> Is there a way to pack and store arbitrary data in the kernel, or do I > >>> need to roll my own? > > > > Sounds a bit like a slab cache to me. > > > > OK cool, can I make that non-swappable? kernel (allocated) memory is non-swappable. > I'm going to be trying to do > this between where kernel swaps a page out and swapped page actually is > written to disk. The result will be a "Swap Zone," in-memory storage of > pages that the rest of the kernel thinks have been swapped to disk. > (Code here will use the swap interface, so the rest of the kernel thinks > it's just swapping; I'll handle whether to pull it out of memory or off > disk behind that) > > The need for packing pages comes because eventually (using above > infrastructure) I'll be taking sets of 32KiB of data and compressing it; > I don't want to pad up to 4095 excess unused bytes if that stuff > compresses to 28KiB+1 :) (more likely 16KiB+1 +/-8KiB) > > This is all, of course, assuming I ever figure out how the heck to get > in the middle of the swapping process. I'm looking at mm/page_io.c > swap_writepage() and friends and scratching my head. I have no idea wtf... > > > >> Write a device driver, kmalloc some buffer, and copy data via a write > >> function from userspace to that buffer. Should be trivial. > >> > >>> 1 excess pages, 4 units wasted memory. > >> Of course, kmalloc only works up to some boundary AFIACS. > > > > 128 KB on some arches. More on a few IIRC. --- ~Randy