From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 6D785B6F7B for ; Mon, 21 Mar 2011 13:23:19 +1100 (EST) Subject: Re: mmotm threatens ppc preemption again From: Benjamin Herrenschmidt To: Hugh Dickins In-Reply-To: References: <1300665188.2402.64.camel@pasglop> <1300672207.2402.205.camel@pasglop> Content-Type: text/plain; charset="UTF-8" Date: Mon, 21 Mar 2011 13:22:30 +1100 Message-ID: <1300674150.2402.207.camel@pasglop> Mime-Version: 1.0 Cc: Jeremy Fitzhardinge , linuxppc-dev@lists.ozlabs.org, Andrew Morton , Peter Zijlstra List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sun, 2011-03-20 at 19:20 -0700, Hugh Dickins wrote: > > As long as the races to avoid are between map/unmap vs. access, yes, it > > -should- be fine, and we used to not do demand faulting on kernel space > > (but for how long ?). I'm wondering why we don't just stick a ptl in > > there or is there a good reason why we can't ? > > We can - but we usually prefer to avoid unnecessary locking. > An arch function which locks init_mm.page_table_lock on powerpc, > but does nothing on others? That still means gratuitous differences between how the normal and kernel page tables are handled. Maybe that's not worth bothering ... Cheers, Ben.