Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752495AbYKRH0S (ORCPT ); Tue, 18 Nov 2008 02:26:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751197AbYKRH0G (ORCPT ); Tue, 18 Nov 2008 02:26:06 -0500 Received: from gate.crashing.org ([63.228.1.57]:58823 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751058AbYKRH0G (ORCPT ); Tue, 18 Nov 2008 02:26:06 -0500 Subject: Re: Large stack usage in fs code (especially for PPC64) From: Benjamin Herrenschmidt To: Linus Torvalds Cc: Steven Rostedt , LKML , Paul Mackerras , linuxppc-dev@ozlabs.org, Andrew Morton , Ingo Molnar , Thomas Gleixner In-Reply-To: References: <1226963596.7178.254.camel@pasglop> Content-Type: text/plain Date: Tue, 18 Nov 2008 18:25:20 +1100 Message-Id: <1226993120.7178.287.camel@pasglop> Mime-Version: 1.0 X-Mailer: Evolution 2.24.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1191 Lines: 30 > > It makes some sort of sense I suppose on very static embedded workloads > > with no swap nor demand paging. > > It makes perfect sense for anything that doesn't use any MMU. To a certain extent. There's two different aspects to having an MMU and in embedded space it's useful to have one and not the other, ie, protection & address space isolation vs. paging. Thus, it does make sense for those embedded devices with few files (mostly a statically linked busybox, a few /dev entries and some app stuff) to use large page sizes. Of course, as soon as they try to populate their ramfs with lots of small files they lose... but mostly, the idea is that the entire working set fits in the TLB and thus the cost of TLB miss becomes irrelevant. Now, regarding the shortcomings of the powerpc server MMU, well, we know them, we know your opinion and mostly share it, and until we can get the HW to change we are stuck with it. Cheers, Ben. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/