From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Wilcox Date: Thu, 02 Sep 2004 15:05:56 +0000 Subject: Re: Problem with no mem_map arg to init functions change? Message-Id: <20040902150556.GJ642@parcelfarce.linux.theplanet.co.uk> List-Id: References: <20040902053659.GG21873@cse.unsw.EDU.AU> In-Reply-To: <20040902053659.GG21873@cse.unsw.EDU.AU> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org On Wed, Sep 01, 2004 at 11:10:30PM -0700, William Lee Irwin III wrote: > You don't thave CONFIG_DISCONTIGMEM set? Why are you bothering with > virtual mem_map if not? If the core helpers are insufficiently > lightweight in the CONFIG_DISCONTIGMEM=n case we are very well going > to have whatever sanction we need to repair it, as this is the common > case among end users of the most predominant hardware and architectures. Ah, basic lack of understanding of what VIRTUAL_MEM_MAP is used for and why it exists. It should be exclusive with DISCONTIGMEM as they both solve the same problem, but in wildly different ways. At the time VIRTUAL_MEM_MAP was put in, the DISCONTIGMEM code was utterly broken and nobody was interested in fixing it ("we have a version in the LSE patch that doesn't suck as much" doesn't help). Both should address the memory map on zx1: 0-1 GB 257-260GB 4-256GB (in practice, the maximum memory you can put in any zx1 box at the moment is 128GB because 4GB DIMMs aren't supported in the rx5670) Without VIRTUAL_MEM_MAP or DISCONTIGMEM, a 2GB zx1 machine would have a 13GB mem_map. So DISCONTIGMEM does away with the global mem_map and VIRTUAL_MEM_MAP constructs a mem_map in vmalloc space rather than the kernel's fixed mapping. If DISCONTIGMEM now works properly, I think VIRTUAL_MEM_MAP can disappear. -- "Next the statesmen will invent cheap lies, putting the blame upon the nation that is attacked, and every man will be glad of those conscience-soothing falsities, and will diligently study them, and refuse to examine any refutations of them; and thus he will by and by convince himself that the war is just, and will thank God for the better sleep he enjoys after this process of grotesque self-deception." -- Mark Twain