From mboxrd@z Thu Jan 1 00:00:00 1970 From: =?utf-8?B?SsO2cm4=?= Engel Subject: Re: [00/41] Large Blocksize Support V7 (adds memmap support) Date: Sun, 16 Sep 2007 19:53:52 +0200 Message-ID: <20070916175352.GB2393@lazybastard.org> References: <20070911060349.993975297@sgi.com> <200709110452.20363.nickpiggin@yahoo.com.au> <20070911121225.GE13132@lazybastard.org> <20070915014449.4f9cdb51.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: =?utf-8?B?SsO2cm4=?= Engel , Nick Piggin , Christoph Lameter , andrea@suse.de, torvalds@linux-foundation.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Christoph Hellwig , Mel Gorman , William Lee Irwin III , David Chinner , Jens Axboe , Badari Pulavarty , Maxim Levitsky , Fengguang Wu , swin wang , totty.lu@gmail.com, hugh@veritas.com To: Andrew Morton Return-path: Received: from lazybastard.de ([212.112.238.170]:38853 "EHLO longford.lazybastard.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752125AbXIPR6H (ORCPT ); Sun, 16 Sep 2007 13:58:07 -0400 Content-Disposition: inline In-Reply-To: <20070915014449.4f9cdb51.akpm@linux-foundation.org> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Sat, 15 September 2007 01:44:49 -0700, Andrew Morton wrote: > On Tue, 11 Sep 2007 14:12:26 +0200 J=C3=B6rn Engel = wrote: >=20 > > While I agree with your concern, those numbers are quite silly. Th= e > > chances of 99.8% of pages being free and the remaining 0.2% being > > perfectly spread across all 2MB large_pages are lower than those of= SHA1 > > creating a collision. >=20 > Actually it'd be pretty easy to craft an application which allocates = seven > pages for pagecache, then one for , then seven for pagecac= he, then > one for , etc. >=20 > I've had test apps which do that sort of thing accidentally. The res= ult > wasn't pretty. I bet! My (false) assumption was the same as Goswin's. If non-movable pages are clearly seperated from movable ones and will evict movable ones before polluting further mixed superpages, Nick's scenario would b= e nearly infinitely impossible. Assumption doesn't reflect current code. Enforcing this assumption would cost extra overhead. The amount of effort to make Christoph's approach work reliably seems substantial and I have no idea whether it would be worth it. J=C3=B6rn --=20 Happiness isn't having what you want, it's wanting what you have. -- unknown - To unsubscribe from this list: send the line "unsubscribe linux-fsdevel= " in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html