From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1750883AbVJKNj0 (ORCPT ); Tue, 11 Oct 2005 09:39:26 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751205AbVJKNjZ (ORCPT ); Tue, 11 Oct 2005 09:39:25 -0400 Received: from smtp208.mail.sc5.yahoo.com ([216.136.130.116]:51805 "HELO smtp208.mail.sc5.yahoo.com") by vger.kernel.org with SMTP id S1750883AbVJKNjZ (ORCPT ); Tue, 11 Oct 2005 09:39:25 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com.au; h=Received:Message-ID:Date:From:User-Agent:X-Accept-Language:MIME-Version:To:CC:Subject:References:In-Reply-To:Content-Type:Content-Transfer-Encoding; b=MguW/qttmHDEV310DdeeC3ZE1V4N/iv7JqpeFnNjSDhNvX3UwatnqJxoewmouEzfo3NipSKmqqGZe4+jA3cBNTJ/CsWWOgHgXnvC2NSVCTofDXbbWmLT8FDZSyTkWTdBq1pQukXIzKyBJESCrH9I5MysA2P9MkSuDGEra7J2sco= ; Message-ID: <434BC095.4050305@yahoo.com.au> Date: Tue, 11 Oct 2005 23:39:33 +1000 From: Nick Piggin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.7.11) Gecko/20050914 Debian/1.7.11-1 X-Accept-Language: en MIME-Version: 1.0 To: Alan Cox CC: Andrew Morton , Hugh Dickins , linux-kernel Subject: Re: [PATCH 2.6.14-rc2-mm2] core remove PageReserved References: <434B7F19.5040808@yahoo.com.au> <1129035883.23677.48.camel@localhost.localdomain> In-Reply-To: <1129035883.23677.48.camel@localhost.localdomain> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Alan Cox wrote: > On Maw, 2005-10-11 at 19:00 +1000, Nick Piggin wrote: > >>A last caveat: the ZERO_PAGE is now refcounted and managed with rmap >>(and thus mapcounted and count towards shared rss). > > > 32000 processes each with 2G mapped as zero pages appears to allow the > refcount to overflow ? > That's right (though I count only 8192 required with 4K page size) - close to impossible on 32-bit architectures, though not so the 64-bit ones, which still use 32-bits for count and mapcount. I was a bit worried about this too, but Hugh didn't think it was a really big a deal - I guess because the real solution for the refcount overflow on 64-bit is to expand the refcount type. Note also that we can exclude ZERO_PAGE from being refcounted, which may be desirable for a scalability perspective on big NUMA machines. The aim with this patch is to provide a patch which is as simple as possible in order to get the mechanism right. But you raise a valid concern and we do need to discuss these peripheral issues and sort them out before it gets merged upstream. Thanks, Nick -- SUSE Labs, Novell Inc. Send instant messages to your online friends http://au.messenger.yahoo.com