Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759315AbWLDTbI (ORCPT ); Mon, 4 Dec 2006 14:31:08 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1759421AbWLDTbH (ORCPT ); Mon, 4 Dec 2006 14:31:07 -0500 Received: from smtp.osdl.org ([65.172.181.25]:58809 "EHLO smtp.osdl.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759315AbWLDTbG (ORCPT ); Mon, 4 Dec 2006 14:31:06 -0500 Date: Mon, 4 Dec 2006 11:30:51 -0800 From: Andrew Morton To: mel@skynet.ie (Mel Gorman) Cc: clameter@sgi.com, Linux Memory Management List , Linux Kernel Mailing List Subject: Re: [PATCH] Add __GFP_MOVABLE for callers to flag allocations that may be migrated Message-Id: <20061204113051.4e90b249.akpm@osdl.org> In-Reply-To: <20061204140747.GA21662@skynet.ie> References: <20061130170746.GA11363@skynet.ie> <20061130173129.4ebccaa2.akpm@osdl.org> <20061201110103.08d0cf3d.akpm@osdl.org> <20061204140747.GA21662@skynet.ie> X-Mailer: Sylpheed version 2.2.7 (GTK+ 2.8.6; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2253 Lines: 43 On Mon, 4 Dec 2006 14:07:47 +0000 mel@skynet.ie (Mel Gorman) wrote: > o copy_strings() and variants are no longer setting the flag as the pages > are not obviously movable when I took a much closer look. > > o The arch function alloc_zeroed_user_highpage() is now called > __alloc_zeroed_user_highpage and takes flags related to > movability that will be applied. alloc_zeroed_user_highpage() > calls __alloc_zeroed_user_highpage() with no additional flags to > preserve existing behavior of the API for out-of-tree users and > alloc_zeroed_user_highpage_movable() sets the __GFP_MOVABLE flag. > > o new_inode() documents that it uses GFP_HIGH_MOVABLE and callers are expected > to call mapping_set_gfp_mask() if that is not suitable. umm, OK. Could we please have some sort of statement pinning down the exact semantics of __GFP_MOVABLE, and what its envisaged applications are? My concern is that __GFP_MOVABLE is useful for fragmentation-avoidance, but useless for memory hot-unplug. So that if/when hot-unplug comes along we'll add more gunk which is a somewhat-superset of the GFP_MOVABLE infrastructure, hence we didn't need the GFP_MOVABLE code. Or something. That depends on how we do hot-unplug, if we do it. I continue to suspect that it'll be done via memory zones: effectively by resurrecting GFP_HIGHMEM. In which case there's little overlap with anti-frag. (btw, I have a suspicion that the most important application of memory hot-unplug will be power management: destructively turning off DIMMs). I'd also like to pin down the situation with lumpy-reclaim versus anti-fragmentation. No offence, but I would of course prefer to avoid merging the anti-frag patches simply based on their stupendous size. It seems to me that lumpy-reclaim is suitable for the e1000 problem, but perhaps not for the hugetlbpage problem. Whereas anti-fragmentation adds vastly more code, but can address both problems? Or something. IOW: big-picture where-do-we-go-from-here stuff. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/