Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S967561Ab2EQScE (ORCPT ); Thu, 17 May 2012 14:32:04 -0400 Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:53467 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S967515Ab2EQScB (ORCPT ); Thu, 17 May 2012 14:32:01 -0400 Date: Thu, 17 May 2012 19:31:39 +0100 From: Catalin Marinas To: Russell King Cc: Peter Zijlstra , Paul Mundt , Andrea Arcangeli , Thomas Gleixner , Rik van Riel , Ingo Molnar , "akpm@linux-foundation.org" , Linus Torvalds , "linux-kernel@vger.kernel.org" , "linux-arch@vger.kernel.org" , "linux-mm@kvack.org" , Benjamin Herrenschmidt , David Miller , Hugh Dickins , Mel Gorman , Nick Piggin , Chris Metcalf , Martin Schwidefsky Subject: Re: [RFC][PATCH 4/6] arm, mm: Convert arm to generic tlb Message-ID: <20120517183139.GA31838@arm.com> References: <20110302175928.022902359@chello.nl> <20110302180259.109909335@chello.nl> <20120517030551.GA11623@linux-sh.org> <20120517093022.GA14666@arm.com> <20120517095124.GN23420@flint.arm.linux.org.uk> <1337254086.4281.26.camel@twins> <20120517160012.GB18593@arm.com> <20120517172215.GB11487@flint.arm.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120517172215.GB11487@flint.arm.linux.org.uk> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3027 Lines: 66 On Thu, May 17, 2012 at 06:22:15PM +0100, Russell King wrote: > On Thu, May 17, 2012 at 05:00:12PM +0100, Catalin Marinas wrote: > > On Thu, May 17, 2012 at 12:28:06PM +0100, Peter Zijlstra wrote: > > > On Thu, 2012-05-17 at 10:51 +0100, Russell King wrote: > > > > On Thu, May 17, 2012 at 10:30:23AM +0100, Catalin Marinas wrote: > > > > > Another minor thing is that on newer ARM processors (Cortex-A15) we > > > > > need the TLB shootdown even on UP systems, so tlb_fast_mode should > > > > > always return 0. Something like below (untested): > > > > > > > > No Catalin, we need this for virtually all ARMv7 CPUs whether they're UP > > > > or SMP, not just for A15, because of the speculative prefetch which can > > > > re-load TLB entries from the page tables at _any_ time. > > > > > > Hmm,. so this is mostly because of the confusion/coupling between > > > tlb_remove_page() and tlb_remove_table() I guess. Since I don't see the > > > freeing of the actual pages being a problem with speculative TLB > > > reloads, just the page-tables. > > > > > > Should we introduce a tlb_remove_table() regardless of > > > HAVE_RCU_TABLE_FREE which always queues the tables regardless of > > > tlb_fast_mode()? > > > > BTW, looking at your tlb-unify branch, does tlb_remove_table() call > > tlb_flush/tlb_flush_mmu before freeing the tables? I can only see > > tlb_remove_page() doing this. On ARM, even UP, we need the TLB flushing > > after clearing the pmd and before freeing the pte page table (and > > ideally doing it less often than at every pte_free_tlb() call). > > Catalin, > > The way TLB shootdown stuff works is that _every_ single bit of memory > which gets freed, whether its a page or a page table, gets added to a > list of pages to be freed. > > So, the sequence is: > - remove pte/pmd/pud/pgd pointers > - add pages, whether they be pages pointed to by pte entries or page tables > to be freed to a list > - when list is sufficiently full, invalidate TLBs > - free list of pages > > That means the pages will not be freed, whether it be a page mapped > into userspace or a page table until such time that the TLB has been > invalidated. > > For page tables, this is done via pXX_free_tlb(), which then calls out > to the arch specific __pXX_free_tlb(), which ultimately then hands the > page table over to tlb_remove_page() to add to the list of to-be-freed > pages. I know that already, not sure why you explained it again (but it's good for future reference). My point was that if we move to HAVE_RCU_FREE_TLB, the other architectures doing this are calling tlb_remove_table() instead of tlb_remove_page() in __p??_free_tlb(). And tlb_remove_table() does not do any TLB maintenance when it can no longer queue pages (batch table overflow). -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/