From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf0-f200.google.com (mail-pf0-f200.google.com [209.85.192.200]) by kanga.kvack.org (Postfix) with ESMTP id AE2B528089F for ; Thu, 9 Feb 2017 01:22:58 -0500 (EST) Received: by mail-pf0-f200.google.com with SMTP id 201so223134413pfw.5 for ; Wed, 08 Feb 2017 22:22:58 -0800 (PST) Received: from out0-136.mail.aliyun.com (out0-136.mail.aliyun.com. [140.205.0.136]) by mx.google.com with ESMTP id x5si9220733pgf.20.2017.02.08.22.22.57 for ; Wed, 08 Feb 2017 22:22:57 -0800 (PST) Reply-To: "Hillf Danton" From: "Hillf Danton" References: <20170208152200.ydlvia2c7lm7ln3t@techsingularity.net> In-Reply-To: <20170208152200.ydlvia2c7lm7ln3t@techsingularity.net> Subject: Re: [PATCH] mm, page_alloc: only use per-cpu allocator for irq-safe requests -fix v2 Date: Thu, 09 Feb 2017 14:22:52 +0800 Message-ID: <00d201d2829c$f233b630$d69b2290$@alibaba-inc.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Content-Language: zh-cn Sender: owner-linux-mm@kvack.org List-ID: To: 'Mel Gorman' , 'Andrew Morton' Cc: 'Thomas Gleixner' , 'Peter Zijlstra' , 'Michal Hocko' , 'Vlastimil Babka' , linux-mm@kvack.org, linux-kernel@vger.kernel.org, 'Ingo Molnar' On February 08, 2017 11:22 PM Mel Gorman wrote: > > preempt_enable_no_resched() was used based on review feedback that had > no strong objection at the time. The thinking was that it avoided adding > a preemption point where one didn't exist before so the feedback was > applied. This reasoning was wrong. > > There was an indirect preemption point as explained by Thomas Gleixner where > an interrupt could set_need_resched() followed by preempt_enable being > a preemption point that matters. This use of preempt_enable_no_resched > is bad from both a mainline and RT perspective and a violation of the > preemption mechanism. Peter Zijlstra noted that "the only acceptable use > of preempt_enable_no_resched() is if the next statement is a schedule() > variant". > > The usage was outright broken and I should have stuck to preempt_enable() > as it was originally developed. It's known from previous tests > that there was no detectable difference to the performance by using > preempt_enable_no_resched(). > > This is a fix to the mmotm patch > mm-page_alloc-only-use-per-cpu-allocator-for-irq-safe-requests.patch > > Signed-off-by: Mel Gorman > --- Thanks for fixing it. Acked-by: Hillf Danton > mm/page_alloc.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index eaecb4b145e6..2a36dad03dac 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -2520,7 +2520,7 @@ void free_hot_cold_page(struct page *page, bool cold) > } > > out: > - preempt_enable_no_resched(); > + preempt_enable(); > } > > /* > @@ -2686,7 +2686,7 @@ static struct page *rmqueue_pcplist(struct zone *preferred_zone, > __count_zid_vm_events(PGALLOC, page_zonenum(page), 1 << order); > zone_statistics(preferred_zone, zone); > } > - preempt_enable_no_resched(); > + preempt_enable(); > return page; > } > -- 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