From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yh0-f53.google.com (mail-yh0-f53.google.com [209.85.213.53]) by kanga.kvack.org (Postfix) with ESMTP id EC01A6B0039 for ; Fri, 27 Jun 2014 08:20:56 -0400 (EDT) Received: by mail-yh0-f53.google.com with SMTP id b6so2934369yha.40 for ; Fri, 27 Jun 2014 05:20:56 -0700 (PDT) Received: from cam-admin0.cambridge.arm.com (cam-admin0.cambridge.arm.com. [217.140.96.50]) by mx.google.com with ESMTP id t15si2896549yha.5.2014.06.27.05.20.55 for ; Fri, 27 Jun 2014 05:20:56 -0700 (PDT) Date: Fri, 27 Jun 2014 13:20:32 +0100 From: Will Deacon Subject: Re: [PATCH 6/6] arm64: mm: Enable RCU fast_gup Message-ID: <20140627122032.GN26276@arm.com> References: <1403710824-24340-1-git-send-email-steve.capper@linaro.org> <1403710824-24340-7-git-send-email-steve.capper@linaro.org> <20140625165003.GI15240@leverpostej> <20140626075605.GB12054@laptop.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140626075605.GB12054@laptop.lan> Sender: owner-linux-mm@kvack.org List-ID: To: Peter Zijlstra Cc: Mark Rutland , Steve Capper , "linux-arm-kernel@lists.infradead.org" , Catalin Marinas , "linux@arm.linux.org.uk" , "linux-arch@vger.kernel.org" , "linux-mm@kvack.org" , "anders.roxell@linaro.org" , "gary.robertson@linaro.org" , "akpm@linux-foundation.org" , "christoffer.dall@linaro.org" , Thomas Gleixner On Thu, Jun 26, 2014 at 08:56:05AM +0100, Peter Zijlstra wrote: > On Wed, Jun 25, 2014 at 05:50:03PM +0100, Mark Rutland wrote: > > Hi Steve, > > > > On Wed, Jun 25, 2014 at 04:40:24PM +0100, Steve Capper wrote: > > > Activate the RCU fast_gup for ARM64. We also need to force THP splits > > > to broadcast an IPI s.t. we block in the fast_gup page walker. As THP > > > splits are comparatively rare, this should not lead to a noticeable > > > performance degradation. > > > > > > Some pre-requisite functions pud_write and pud_page are also added. > > > > > > Signed-off-by: Steve Capper > > > --- > > > arch/arm64/Kconfig | 3 +++ > > > arch/arm64/include/asm/pgtable.h | 11 ++++++++++- > > > arch/arm64/mm/flush.c | 19 +++++++++++++++++++ > > > 3 files changed, 32 insertions(+), 1 deletion(-) > > > > [...] > > > > > diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c > > > index e4193e3..ddf96c1 100644 > > > --- a/arch/arm64/mm/flush.c > > > +++ b/arch/arm64/mm/flush.c > > > @@ -103,3 +103,22 @@ EXPORT_SYMBOL(flush_dcache_page); > > > */ > > > EXPORT_SYMBOL(flush_cache_all); > > > EXPORT_SYMBOL(flush_icache_range); > > > + > > > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE > > > +#ifdef CONFIG_HAVE_RCU_TABLE_FREE > > > +static void thp_splitting_flush_sync(void *arg) > > > +{ > > > +} > > > + > > > +void pmdp_splitting_flush(struct vm_area_struct *vma, unsigned long address, > > > + pmd_t *pmdp) > > > +{ > > > + pmd_t pmd = pmd_mksplitting(*pmdp); > > > + VM_BUG_ON(address & ~PMD_MASK); > > > + set_pmd_at(vma->vm_mm, address, pmdp, pmd); > > > + > > > + /* dummy IPI to serialise against fast_gup */ > > > + smp_call_function(thp_splitting_flush_sync, NULL, 1); > > > > Is there some reason we can't use kick_all_cpus_sync()? > > Yes that would be equivalent. But looking at that, I worry about the > smp_mb(); archs are supposed to make sure IPIs are serializing. Agreed; smp_call_function would be hopelessly broken if that wasn't true (at least, everywhere I've used it ;) Will -- 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/ . Don't email: email@kvack.org