From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758597AbYBFTsr (ORCPT ); Wed, 6 Feb 2008 14:48:47 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753974AbYBFTsi (ORCPT ); Wed, 6 Feb 2008 14:48:38 -0500 Received: from extu-mxob-1.symantec.com ([216.10.194.28]:37738 "EHLO extu-mxob-1.symantec.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751824AbYBFTsh (ORCPT ); Wed, 6 Feb 2008 14:48:37 -0500 Date: Wed, 6 Feb 2008 19:48:22 +0000 (GMT) From: Hugh Dickins X-X-Sender: hugh@blonde.site To: "H. Peter Anvin" cc: Tomasz Chmielewski , LKML , Mika Lawando Subject: Re: What is the limit size of tmpfs /dev/shm ? In-Reply-To: <47AA0A2E.30701@zytor.com> Message-ID: References: <47A9CA0E.3030507@wpkg.org> <47AA0A2E.30701@zytor.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 6 Feb 2008, H. Peter Anvin wrote: > Hugh Dickins wrote: > > > > Don't forget that tmpfs overflows into swap, so you could save money > > by adding adding more swap and cutting down on the RAM: though of > > course that will perform very poorly once it's actually using the > > swap, probably not the direction you want to go in. > > It can still outperform conventional disk filesystems, however, mostly because > it doesn't have to worry one iota about consistency. In theory, yes, and should be true in practice before it hits swap. But I think you'll find our swap handling is too primitive for tmpfs to perform well once we hit swap. Most filesystems pay considerable attention to good performance within their constraints of correctness. Whereas with tmpfs we've just never worried about the performance once swapping. It's used so you don't lose your data, but if you're really expecting to be going to disk very much, better start with a filesystem really designed for that. Hugh