From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f69.google.com (mail-pl0-f69.google.com [209.85.160.69]) by kanga.kvack.org (Postfix) with ESMTP id A5A076B0006 for ; Mon, 26 Feb 2018 20:55:17 -0500 (EST) Received: by mail-pl0-f69.google.com with SMTP id l5-v6so3114035pli.8 for ; Mon, 26 Feb 2018 17:55:17 -0800 (PST) Received: from mga11.intel.com (mga11.intel.com. [192.55.52.93]) by mx.google.com with ESMTPS id t18si7718122pfg.246.2018.02.26.17.55.15 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 26 Feb 2018 17:55:16 -0800 (PST) Date: Tue, 27 Feb 2018 09:56:13 +0800 From: Aaron Lu Subject: Re: [PATCH v3 1/3] mm/free_pcppages_bulk: update pcp->count inside Message-ID: <20180227015613.GA9141@intel.com> References: <20180226135346.7208-1-aaron.lu@intel.com> <20180226135346.7208-2-aaron.lu@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: David Rientjes Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Huang Ying , Dave Hansen , Kemi Wang , Tim Chen , Andi Kleen , Michal Hocko , Vlastimil Babka , Mel Gorman , Matthew Wilcox On Mon, Feb 26, 2018 at 01:48:14PM -0800, David Rientjes wrote: > On Mon, 26 Feb 2018, Aaron Lu wrote: > > > Matthew Wilcox found that all callers of free_pcppages_bulk() currently > > update pcp->count immediately after so it's natural to do it inside > > free_pcppages_bulk(). > > > > No functionality or performance change is expected from this patch. > > > > Suggested-by: Matthew Wilcox > > Signed-off-by: Aaron Lu > > --- > > mm/page_alloc.c | 10 +++------- > > 1 file changed, 3 insertions(+), 7 deletions(-) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index cb416723538f..3154859cccd6 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -1117,6 +1117,7 @@ static void free_pcppages_bulk(struct zone *zone, int count, > > int batch_free = 0; > > bool isolated_pageblocks; > > > > + pcp->count -= count; > > spin_lock(&zone->lock); > > isolated_pageblocks = has_isolate_pageblock(zone); > > > > Why modify pcp->count before the pages have actually been freed? When count is still count and not zero after pages have actually been freed :-) > > I doubt that it matters too much, but at least /proc/zoneinfo uses > zone->lock. I think it should be done after the lock is dropped. Agree that it looks a bit weird to do it beforehand and I just want to avoid adding one more local variable here. pcp->count is not protected by zone->lock though so even we do it after dropping the lock, it could still happen that zoneinfo shows a wrong value of pcp->count while it should be zero(this isn't a problem since zoneinfo doesn't need to be precise). Anyway, I'll follow your suggestion here to avoid confusion. > Otherwise, looks good. Thanks for taking a look at this. -- 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