From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Hildenbrand Subject: Re: [RFC 0/2] Reenable might_sleep() checks for might_fault() when atomic Date: Thu, 27 Nov 2014 16:19:05 +0100 Message-ID: <20141127161905.7c6220ee@thinkpad-w530> References: <20141126151729.GB9612@redhat.com> <20141126152334.GA9648@redhat.com> <20141126163207.63810fcb@thinkpad-w530> <20141126154717.GB10568@redhat.com> <5475FAB1.1000802@de.ibm.com> <20141126163216.GB10850@redhat.com> <547604FC.4030300@de.ibm.com> <20141126170447.GC11202@redhat.com> <20141127070919.GA4390@osiris> <20141127090301.3ddc3077@thinkpad-w530> <20141127120441.GB4390@osiris> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Thomas Gleixner Cc: Heiko Carstens , "Michael S. Tsirkin" , Christian Borntraeger , linuxppc-dev@lists.ozlabs.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, benh@kernel.crashing.org, paulus@samba.org, akpm@linux-foundation.org, schwidefsky@de.ibm.com, mingo@kernel.org List-Id: linux-arch.vger.kernel.org > OTOH, there is no reason why we need to disable preemption over that > page_fault_disabled() region. There are code pathes which really do > not require to disable preemption for that. > > We have that seperated in preempt-rt for obvious reasons and IIRC > Peter Zijlstra tried to distangle it in mainline some time ago. I > forgot why that never got merged. > Of course, we can completely separate that in our page fault code by doing pagefault_disabled() checks instead of in_atomic() checks (even in add on patches later). > We tie way too much stuff on the preemption count already, which is a > mightmare because we have no clear distinction of protection > scopes. Although it might not be optimal, but keeping a separate counter for pagefault_disable() as part of the preemption counter seems to be the only doable thing right now. I am not sure if a completely separated counter is even possible, increasing the size of thread_info. I am working on a prototype right now. Thanks! > > Thanks, > > tglx > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e06smtp12.uk.ibm.com ([195.75.94.108]:46961 "EHLO e06smtp12.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751169AbaK0PTM (ORCPT ); Thu, 27 Nov 2014 10:19:12 -0500 Received: from /spool/local by e06smtp12.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 27 Nov 2014 15:19:11 -0000 Date: Thu, 27 Nov 2014 16:19:05 +0100 From: David Hildenbrand Subject: Re: [RFC 0/2] Reenable might_sleep() checks for might_fault() when atomic Message-ID: <20141127161905.7c6220ee@thinkpad-w530> In-Reply-To: References: <20141126151729.GB9612@redhat.com> <20141126152334.GA9648@redhat.com> <20141126163207.63810fcb@thinkpad-w530> <20141126154717.GB10568@redhat.com> <5475FAB1.1000802@de.ibm.com> <20141126163216.GB10850@redhat.com> <547604FC.4030300@de.ibm.com> <20141126170447.GC11202@redhat.com> <20141127070919.GA4390@osiris> <20141127090301.3ddc3077@thinkpad-w530> <20141127120441.GB4390@osiris> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Thomas Gleixner Cc: Heiko Carstens , "Michael S. Tsirkin" , Christian Borntraeger , linuxppc-dev@lists.ozlabs.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, benh@kernel.crashing.org, paulus@samba.org, akpm@linux-foundation.org, schwidefsky@de.ibm.com, mingo@kernel.org Message-ID: <20141127151905.PqewDf6KMo6St0Cja_XWr04_gSOnC43Y5nkac4ITtcM@z> > OTOH, there is no reason why we need to disable preemption over that > page_fault_disabled() region. There are code pathes which really do > not require to disable preemption for that. > > We have that seperated in preempt-rt for obvious reasons and IIRC > Peter Zijlstra tried to distangle it in mainline some time ago. I > forgot why that never got merged. > Of course, we can completely separate that in our page fault code by doing pagefault_disabled() checks instead of in_atomic() checks (even in add on patches later). > We tie way too much stuff on the preemption count already, which is a > mightmare because we have no clear distinction of protection > scopes. Although it might not be optimal, but keeping a separate counter for pagefault_disable() as part of the preemption counter seems to be the only doable thing right now. I am not sure if a completely separated counter is even possible, increasing the size of thread_info. I am working on a prototype right now. Thanks! > > Thanks, > > tglx >