From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751377AbXCDBEJ (ORCPT ); Sat, 3 Mar 2007 20:04:09 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751388AbXCDBEJ (ORCPT ); Sat, 3 Mar 2007 20:04:09 -0500 Received: from tomts41.bellnexxia.net ([209.226.175.98]:57469 "EHLO tomts41-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751377AbXCDBEI (ORCPT ); Sat, 3 Mar 2007 20:04:08 -0500 X-Greylist: delayed 2944 seconds by postgrey-1.27 at vger.kernel.org; Sat, 03 Mar 2007 20:04:07 EST Subject: Re: userspace pagecache management tool From: Eric St-Laurent To: Andrew Morton Cc: linux-kernel@vger.kernel.org In-Reply-To: <20070303122935.f1ab0067.akpm@linux-foundation.org> References: <20070303122935.f1ab0067.akpm@linux-foundation.org> Content-Type: text/plain Date: Sat, 03 Mar 2007 19:14:59 -0500 Message-Id: <1172967299.8493.34.camel@perkele> Mime-Version: 1.0 X-Mailer: Evolution 2.9.92 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2007-03-03 at 12:29 -0800, Andrew Morton wrote: > There is much more which could be done to make this code smarter, but I > think the lesson here is that we can produce a far, far better result doing > this work in userspace than we could ever hope to do with an in-kernel > implementation. There are some enhancement suggestions in the > documentation file. While I think that more user space applications should use fadvise() to avoid polluting the page cache with unneeded data, I still think the kernel should be more fair in regard to page cache management. Personally, I've experienced some sluggish performance after copying large files around. Even more when using NFS. It's difficult to file a bug report for "interactive feel", I don't know how to measure it. I just feel it's a weak aspect of the OS. Surely it's possible to make the kernel a little bit better to protect the page cache from abuse, from simple or badly designed applications. Why fairness is provided by the process scheduler with good results, yet it somewhat easy for a process to cause slowdowns from page cache usage. My personal opinion is that the VM seem tuned for database types workloads. Of course, making the page cache more fair to prevent one process to use most of it will most likely slowdown database type applications. Maybe the situation should be reversed, much like the process scheduler. Fairness by default, and the possibility to request for more system resources by asking for them with necessary privileges. Much like SCHED_FIFO policy. - Eric