Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754618AbYKQVTY (ORCPT ); Mon, 17 Nov 2008 16:19:24 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752114AbYKQVTM (ORCPT ); Mon, 17 Nov 2008 16:19:12 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:36372 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751997AbYKQVTL (ORCPT ); Mon, 17 Nov 2008 16:19:11 -0500 Date: Mon, 17 Nov 2008 13:18:44 -0800 (PST) From: Linus Torvalds To: Steven Rostedt cc: LKML , Paul Mackerras , Benjamin Herrenschmidt , linuxppc-dev@ozlabs.org, Andrew Morton , Ingo Molnar , Thomas Gleixner Subject: Re: Large stack usage in fs code (especially for PPC64) In-Reply-To: Message-ID: References: User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) 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 Content-Length: 1663 Lines: 43 On Mon, 17 Nov 2008, Steven Rostedt wrote: > > Here's my stack after boot up with CONFIG_IRQSTACKS set. Seems that > softirqs still use the same stack as the process. Yes. > This is still 12K. Kind of big even for a 16K stack. And while that 1kB+ stack slot for block_read_full_page still stands out like a sore thumb, I do agree that there's way too many other functions too with big stack frames. I do wonder just _what_ it is that causes the stack frames to be so horrid. For example, you have 18) 8896 160 .kmem_cache_alloc+0xfc/0x140 and I'm looking at my x86-64 compile, and it has a stack frame of just 8 bytes (!) for local variables plus the save/restore area (which looks like three registers plus frame pointer plus return address). IOW, if I'm looking at the code right (so big caveat: I did _not_ do a real stack dump!) the x86-64 stack cost for that same function is on the order of 48 bytes. Not 160. Where does that factor-of-three+ difference come from? From the numbers, I suspect ppc64 has a 32-byte stack alignment, which may be part of it, and I guess the compiler is more eager to use all those extra registers and will happily have many more callee-saved regs that are actually used. But that still a _lot_ of extra stack. Of course, you may have things like spinlock debugging etc enabled. Some of our debugging options do tend to blow things up. Linus -- 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/