Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753576AbcKGQuv (ORCPT ); Mon, 7 Nov 2016 11:50:51 -0500 Received: from mail-ua0-f174.google.com ([209.85.217.174]:36208 "EHLO mail-ua0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752147AbcKGQus (ORCPT ); Mon, 7 Nov 2016 11:50:48 -0500 MIME-Version: 1.0 In-Reply-To: References: <1477149440-12478-1-git-send-email-hch@lst.de> <1477149440-12478-5-git-send-email-hch@lst.de> <25c117ae-6d06-9846-6a88-ae6221ad6bfe@virtuozzo.com> From: Joel Fernandes Date: Mon, 7 Nov 2016 08:50:46 -0800 Message-ID: Subject: Re: [PATCH 4/7] mm: defer vmalloc from atomic context To: Andrey Ryabinin Cc: Christoph Hellwig , Andrew Morton , Jisheng Zhang , Chris Wilson , John Dias , "open list:MEMORY MANAGEMENT" , linux-rt-users@vger.kernel.org, LKML , Andy Lutomirski Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1719 Lines: 53 On Mon, Nov 7, 2016 at 7:01 AM, Andrey Ryabinin wrote: > On 11/05/2016 06:43 AM, Joel Fernandes wrote: >> On Mon, Oct 24, 2016 at 8:44 AM, Andrey Ryabinin >> wrote: >>> >>> >>> On 10/22/2016 06:17 PM, Christoph Hellwig wrote: >>>> We want to be able to use a sleeping lock for freeing vmap to keep >>>> latency down. For this we need to use the deferred vfree mechanisms >>>> no only from interrupt, but from any atomic context. >>>> >>>> Signed-off-by: Christoph Hellwig >>>> --- >>>> mm/vmalloc.c | 2 +- >>>> 1 file changed, 1 insertion(+), 1 deletion(-) >>>> >>>> diff --git a/mm/vmalloc.c b/mm/vmalloc.c >>>> index a4e2cec..bcc1a64 100644 >>>> --- a/mm/vmalloc.c >>>> +++ b/mm/vmalloc.c >>>> @@ -1509,7 +1509,7 @@ void vfree(const void *addr) >>>> >>>> if (!addr) >>>> return; >>>> - if (unlikely(in_interrupt())) { >>>> + if (unlikely(in_atomic())) { >>> >>> in_atomic() cannot always detect atomic context, thus it shouldn't be used here. >>> You can add something like vfree_in_atomic() and use it in atomic call sites. >>> >> >> So because in_atomic doesn't work for !CONFIG_PREEMPT kernels, can we >> always defer the work in these cases? >> >> So for non-preemptible kernels, we always defer: >> >> if (!IS_ENABLED(CONFIG_PREEMPT) || in_atomic()) { >> // defer >> } >> >> Is this fine? Or any other ideas? >> > > What's wrong with my idea? > We can add vfree_in_atomic() and use it to free vmapped stacks > and for any other places where vfree() used 'in_atomict() && !in_interrupt()' context. Yes, this sounds like a better idea as there may not be that many callers and my idea may hurt perf. Thanks, Joel