From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 15 Feb 2007 18:48:00 -0800 From: Andrew Morton Subject: Re: [RFC] Remove unswappable anonymous pages off the LRU Message-Id: <20070215184800.e2820947.akpm@linux-foundation.org> In-Reply-To: References: <20070215171355.67c7e8b4.akpm@linux-foundation.org> <45D50B79.5080002@mbligh.org> <20070215174957.f1fb8711.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Christoph Lameter Cc: Martin Bligh , linux-mm@kvack.org, Nick Piggin , Peter Zijlstra , KAMEZAWA Hiroyuki , Rik van Riel List-ID: On Thu, 15 Feb 2007 18:34:12 -0800 (PST) Christoph Lameter wrote: > On Thu, 15 Feb 2007, Andrew Morton wrote: > > > Guys, this page-flag problem is really serious. -mm adds PG_mlocked and > > PG_readahead and the ext4 patches add PG_booked (am currently fighting the > > good fight there). There's ongoing steady growth in these things and soon > > we're going to be in a lot of pain. > > Well is it possible to restrict some of the features to 64 bit only? There > we have lots of page flags. We discussed that a while back and iirc ia64 has gone and gobbled most of the upper 32bits. Someone went and added some ascii art around the PG_uncached definition but it is incomprehensible. It seems to claim that ia64 has gone and used all 32 bits, dammit. If so, some adjustments to ia64 might be called for. > One additional measure that may be possible is to have a page type field > (maybe 3 bits long) that would consolidate a series of page flags that > cannot occur together. But then we have issues with the atomicity of > updates to that field. > > F.e. > > page_type = { SLAB, LRU, MLOCK, RESERVED, BUDDY, } Yeah, maybe. There doesn't seem to be a lot of room for that though - a lot of those flags are quite independent and can occur simultaneously. Maybe PageSwapCache can be worked out by other means. The two swsusp bits can be removed: they're only needed at suspend/resume time and can be replaced by an external data structure. I still reckon there must be a way to avoid PG_buddy but Martin put up stiff-and-squealy resistance when I resisted the addition of that. -- 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