From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 13 Jan 2005 03:09:14 +0000 (GMT) From: Hugh Dickins Subject: Re: page table lock patch V15 [0/7]: overview In-Reply-To: <41E5B7AD.40304@yahoo.com.au> Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Sender: owner-linux-mm@kvack.org Return-Path: To: Nick Piggin Cc: Andrew Morton , clameter@sgi.com, torvalds@osdl.org, ak@muc.de, linux-mm@kvack.org, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, benh@kernel.crashing.org List-ID: On Thu, 13 Jan 2005, Nick Piggin wrote: > Andrew Morton wrote: > > Note that this was with my ptl removal patches. I can't see why Christoph's > would have _any_ extra overhead as they are, but it looks to me like they're > lacking in atomic ops. So I'd expect something similar for Christoph's when > they're properly atomic. > > > Look, -7% on a 2-way versus +700% on a many-way might well be a tradeoff we > > agree to take. But we need to fully understand all the costs and benefits. > > I think copy_page_range is the one to keep an eye on. Christoph's currently lack set_pte_atomics in the fault handlers, yes. But I don't see why they should need set_pte_atomics in copy_page_range (which is why I persuaded him to drop forcing set_pte to atomic). dup_mmap has down_write of the src mmap_sem, keeping out any faults on that. copy_pte_range has spin_lock of the dst page_table_lock and the src page_table_lock, keeping swapout away from those. Why would atomic set_ptes be needed there? Probably in yours, but not in Christoph's. Hugh -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: aart@kvack.org