From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f200.google.com (mail-pg1-f200.google.com [209.85.215.200]) by kanga.kvack.org (Postfix) with ESMTP id 69AEB6B0007 for ; Mon, 5 Nov 2018 01:10:20 -0500 (EST) Received: by mail-pg1-f200.google.com with SMTP id o17so7285656pgi.14 for ; Sun, 04 Nov 2018 22:10:20 -0800 (PST) Received: from mga14.intel.com (mga14.intel.com. [192.55.52.115]) by mx.google.com with ESMTPS id i13-v6si42073056pgd.311.2018.11.04.22.10.18 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 04 Nov 2018 22:10:19 -0800 (PST) Date: Mon, 5 Nov 2018 14:10:16 +0800 From: Aaron Lu Subject: Re: [PATCH 1/2] mm: use kvzalloc for swap_info_struct allocation Message-ID: <20181105061016.GA4502@intel.com> References: <37b60523-d085-71e9-fef9-80b90bfcef18@virtuozzo.com> <87wopsbb5v.fsf@yhuang-dev.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: Vasily Averin Cc: "Huang, Ying" , linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org On Mon, Nov 05, 2018 at 07:59:13AM +0300, Vasily Averin wrote: > > > On 11/5/18 3:50 AM, Huang, Ying wrote: > > Vasily Averin writes: > > > >> commit a2468cc9bfdf ("swap: choose swap device according to numa node") > >> increased size of swap_info_struct up to 44 Kbytes, now it requires > >> 4th order page. > > > > Why swap_info_struct could be so large? Because MAX_NUMNODES could be > > thousands so that 'avail_lists' field could be tens KB? If so, I think > > it's fair to use kvzalloc(). Can you add one line comment? Because > > struct swap_info_struct is quite small in default configuration. > > I was incorrect not 44Kb but 40kb should be here. > We have found CONFIG_NODES_SHIFT=10 in new RHEL7 update 6 kernel, > default ubuntu kernels have the same setting too. > > crash> struct swap_info_struct -o > struct swap_info_struct { > [0] unsigned long flags; > [8] short prio; > ... > [140] spinlock_t lock; > [144] struct plist_node list; > [184] struct plist_node avail_lists[1024]; <<<< here So every 'struct plist_node' takes 40 bytes and 1024 of them take a total of 40960 bytes, which is 10 pages and need an order-4 page to host them. It looks a little too much, especially consider most of the space will left be unused since most systems have nodes <= 4. I didn't realize this problem when developing this patch, thanks for pointing this out. I think using kvzalloc() as is done by your patch is better here as it can avoid possible failure of swapon. Acked-by: Aaron Lu BTW, for systems with few swap devices this may not be a big deal, but according to your description, your workload will create a lot of swap devices and each of them will likely cause an order-4 unmovable pages allocated(when kvzalloc() doesn't fallback). I was thinking maybe we should convert avail_lists to a pointer in swap_info_struct and use vzalloc() for it. Thanks, Aaron > [41144] struct swap_cluster_info *cluster_info; > [41152] struct swap_cluster_list free_clusters; > ... > [41224] spinlock_t cont_lock; > } > SIZE: 41232 > > struct swap_info_struct { > ... > RH_KABI_EXTEND(struct plist_node avail_lists[MAX_NUMNODES]) /* entry in swap_avail_head */ > ... > } > > #define MAX_NUMNODES (1 << NODES_SHIFT) > > #ifdef CONFIG_NODES_SHIFT > #define NODES_SHIFT CONFIG_NODES_SHIFT > #else > #define NODES_SHIFT 0 > #endif > > /boot/config-4.15.0-38-generic:CONFIG_NODES_SHIFT=10 >