From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1767115AbXDTOr0 (ORCPT ); Fri, 20 Apr 2007 10:47:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1767116AbXDTOr0 (ORCPT ); Fri, 20 Apr 2007 10:47:26 -0400 Received: from holomorphy.com ([66.93.40.71]:57087 "EHLO holomorphy.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1767115AbXDTOrO (ORCPT ); Fri, 20 Apr 2007 10:47:14 -0400 Date: Fri, 20 Apr 2007 07:47:26 -0700 From: William Lee Irwin III To: Mel Gorman Cc: Christoph Lameter , linux-kernel@vger.kernel.org, Peter Zijlstra , Nick Piggin , Andi Kleen , Paul Jackson , Dave Chinner Subject: Re: [RFC 7/8] Enhance ramfs to support higher order pages Message-ID: <20070420144726.GI31925@holomorphy.com> References: <20070419163504.11948.58487.sendpatchset@schroedinger.engr.sgi.com> <20070419163540.11948.51549.sendpatchset@schroedinger.engr.sgi.com> <20070420134226.GA16878@skynet.ie> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20070420134226.GA16878@skynet.ie> Organization: The Domain of Holomorphy User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 20, 2007 at 02:42:27PM +0100, Mel Gorman wrote: > That's fair enough for the moment but relaxing would make ramfs > potentially usable as a replacement for hugetlbfs so there would be just > one ram-based filesystem instead of two. Careful there. mmap() needs more than this. (1) mapping->order is variable within an fs, so the architectural code would need some vague awareness of the underlying page size being variable unless the fs restricts it properly. (2) by and large even large ptes are assumed to map a single object; where mapping->order exceeds the next smallest TLB entry size some potentially intricate machinations are required unless mapping->order restriction is used to avoid it. (3) a backward compatibility wrapper for expand-on-mmap() semantics is needed, among other things. (4) various odd hugetlb things like quotas are in there (5) There are doubtless several oddities about SHM_HUGETLB to emulate that would not be automatic when substituting such an extended ramfs for hugetlbfs in ipc/shm.c (6) ->get_unmapped_area() horrors. The hugetlbfs fs stub has by and large been a huge embarrassment to me, so I'd welcome the opportunity to foist off the vfs lifting onto ramfs. I'd be happier with real superpages, but it's not my kernel. -- wli