From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from d01relay04.pok.ibm.com (d01relay04.pok.ibm.com [9.56.227.236]) by e1.ny.us.ibm.com (8.12.11/8.12.11) with ESMTP id j94GFCUd012820 for ; Tue, 4 Oct 2005 12:15:12 -0400 Received: from d01av02.pok.ibm.com (d01av02.pok.ibm.com [9.56.224.216]) by d01relay04.pok.ibm.com (8.12.10/NCO/VERS6.7) with ESMTP id j94GFChH104350 for ; Tue, 4 Oct 2005 12:15:12 -0400 Received: from d01av02.pok.ibm.com (loopback [127.0.0.1]) by d01av02.pok.ibm.com (8.12.11/8.13.3) with ESMTP id j94GFBMa018239 for ; Tue, 4 Oct 2005 12:15:11 -0400 Subject: Re: sparsemem & sparsemem extreme question From: Dave Hansen In-Reply-To: <20051004065030.GA21741@osiris.boeblingen.de.ibm.com> References: <20051004065030.GA21741@osiris.boeblingen.de.ibm.com> Content-Type: text/plain Date: Tue, 04 Oct 2005 09:15:02 -0700 Message-Id: <1128442502.20208.6.camel@localhost> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Heiko Carstens Cc: linux-mm List-ID: On Tue, 2005-10-04 at 08:50 +0200, Heiko Carstens wrote: > I'm just wondering why there is all this indirection stuff here and why not > have one contiguous aray of struct pages (residing in the vmalloc area) that > deals with whatever size of memory an architecture wants to support. This is exactly what ia64 does today. Programatically, it does remove a layer of indirection. However, there are some data structures that have to be traversed during a lookup: the page tables. Granted, the TLB will provide some caching, but a lookup on ia64 can potentially be much more expensive than the two cacheline misses that sparsemem extreme might have. In the end no one has ever produced any compelling performance reason to use a vmem_map (as ia64 calls it). In addition, sparsemem doesn't cause any known performance regressions, either. -- Dave -- 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: email@kvack.org