From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx153.postini.com [74.125.245.153]) by kanga.kvack.org (Postfix) with SMTP id 201196B00EC for ; Thu, 17 May 2012 13:23:49 -0400 (EDT) Date: Thu, 17 May 2012 18:22:15 +0100 From: Russell King Subject: Re: [RFC][PATCH 4/6] arm, mm: Convert arm to generic tlb Message-ID: <20120517172215.GB11487@flint.arm.linux.org.uk> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120517160012.GB18593@arm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Catalin Marinas 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 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. -- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of: -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org