From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f70.google.com (mail-pl0-f70.google.com [209.85.160.70]) by kanga.kvack.org (Postfix) with ESMTP id 682DE6B0006 for ; Thu, 22 Feb 2018 20:41:52 -0500 (EST) Received: by mail-pl0-f70.google.com with SMTP id b6so3150305plx.3 for ; Thu, 22 Feb 2018 17:41:52 -0800 (PST) Received: from mga03.intel.com (mga03.intel.com. [134.134.136.65]) by mx.google.com with ESMTPS id g63si955187pfb.52.2018.02.22.17.41.51 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 22 Feb 2018 17:41:51 -0800 (PST) Date: Fri, 23 Feb 2018 09:42:46 +0800 From: Aaron Lu Subject: Re: [PATCH v2 1/2] free_pcppages_bulk: do not hold lock when picking pages to free Message-ID: <20180223014245.GB4338@intel.com> References: <20180124023050.20097-1-aaron.lu@intel.com> <20180124163926.c7ptagn655aeiut3@techsingularity.net> <20180125072144.GA27678@intel.com> <20180215124644.GA12360@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180215124644.GA12360@bombadil.infradead.org> Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox Cc: Mel Gorman , 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 On Thu, Feb 15, 2018 at 04:46:44AM -0800, Matthew Wilcox wrote: > On Thu, Jan 25, 2018 at 03:21:44PM +0800, Aaron Lu wrote: > > When freeing a batch of pages from Per-CPU-Pages(PCP) back to buddy, > > the zone->lock is held and then pages are chosen from PCP's migratetype > > list. While there is actually no need to do this 'choose part' under > > lock since it's PCP pages, the only CPU that can touch them is us and > > irq is also disabled. > > I have no objection to this patch. If you're looking for ideas for > future improvement though, I wonder whether using a LIST_HEAD is the > best way to store these pages temporarily. If you batch them into a > pagevec and then free the entire pagevec, the CPU should be a little > faster scanning a short array than walking a linked list. Thanks for the suggestion. > It would also puts a hard boundary on how long zone->lock is held, as > you'd drop it and go back for another batch after 15 pages. That might > be bad, of course. Yes that's a concern. As Mel reponded in another email, I think I'll just keep using list here. > > Another minor change I'd like to see is free_pcpages_bulk updating > pcp->count itself; all of the callers do it currently. Sounds good, I'll prepare a separate patch for this, thanks! -- 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