From mboxrd@z Thu Jan 1 00:00:00 1970 Content-class: urn:content-classes:message MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 8BIT Subject: RE: [RFC/PATCH] pfn_valid() more generic : arch independent part[0/2] Date: Thu, 7 Oct 2004 08:53:32 -0700 Message-ID: From: "Luck, Tony" Sender: owner-linux-mm@kvack.org Return-Path: To: "Martin J. Bligh" , Hiroyuki KAMEZAWA Cc: LinuxIA64 , linux-mm List-ID: >The normal way to fix the above is just to have a bitmap array >to test - in your case a 1GB granularity would be sufficicent. That >takes < 1 word to implement for the example above ;-) In the general case you need a bit for each granule (since that is the unit that the kernel admits/denies the existence of memory). But the really sparse systems end up with a large bitmap. SGI Altix uses 49 physical address bits, and a granule size of 16MB ... so we need 2^25 bits ... i.e. 4MBbytes. While that's a drop in the ocean on a 4TB machine, it still seems a pointless waste. -Tony -- 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