From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id 4E7636B088F for ; Fri, 16 Nov 2018 03:45:59 -0500 (EST) Received: by mail-ed1-f71.google.com with SMTP id h25-v6so11407501eds.21 for ; Fri, 16 Nov 2018 00:45:59 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id q1-v6si5723443ejk.0.2018.11.16.00.45.57 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 16 Nov 2018 00:45:58 -0800 (PST) Date: Fri, 16 Nov 2018 09:45:56 +0100 From: Michal Hocko Subject: Re: [PATCH] mm/swap: use nr_node_ids for avail_lists in swap_info_struct Message-ID: <20181116084556.GB14706@dhcp22.suse.cz> References: <20181115083847.GA11129@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181115083847.GA11129@intel.com> Sender: owner-linux-mm@kvack.org List-ID: To: Aaron Lu Cc: linux-mm , lkml , Vasily Averin , Huang Ying , Andrew Morton On Thu 15-11-18 16:38:47, Aaron Lu wrote: > Since commit a2468cc9bfdf ("swap: choose swap device according to > numa node"), avail_lists field of swap_info_struct is changed to > an array with MAX_NUMNODES elements. This made swap_info_struct > size increased to 40KiB and needs an order-4 page to hold it. > > This is not optimal in that: > 1 Most systems have way less than MAX_NUMNODES(1024) nodes so it > is a waste of memory; > 2 It could cause swapon failure if the swap device is swapped on > after system has been running for a while, due to no order-4 > page is available as pointed out by Vasily Averin. > > Solve the above two issues by using nr_node_ids(which is the actual > possible node number the running system has) for avail_lists instead > of MAX_NUMNODES. > > nr_node_ids is unknown at compile time so can't be directly used > when declaring this array. What I did here is to declare avail_lists > as zero element array and allocate space for it when allocating > space for swap_info_struct. The reason why keep using array but > not pointer is plist_for_each_entry needs the field to be part > of the struct, so pointer will not work. > > This patch is on top of Vasily Averin's fix commit. I think the > use of kvzalloc for swap_info_struct is still needed in case > nr_node_ids is really big on some systems. I haven't seen any system with a huge nr_node_ids but using kvzalloc is not harmfull. > Cc: Vasily Averin > Cc: Michal Hocko > Cc: Huang Ying > Signed-off-by: Aaron Lu Acked-by: Michal Hocko > --- > include/linux/swap.h | 11 ++++++++++- > mm/swapfile.c | 3 ++- > 2 files changed, 12 insertions(+), 2 deletions(-) > > diff --git a/include/linux/swap.h b/include/linux/swap.h > index d8a07a4f171d..3d3630b3f63d 100644 > --- a/include/linux/swap.h > +++ b/include/linux/swap.h > @@ -233,7 +233,6 @@ struct swap_info_struct { > unsigned long flags; /* SWP_USED etc: see above */ > signed short prio; /* swap priority of this type */ > struct plist_node list; /* entry in swap_active_head */ > - struct plist_node avail_lists[MAX_NUMNODES];/* entry in swap_avail_heads */ > signed char type; /* strange name for an index */ > unsigned int max; /* extent of the swap_map */ > unsigned char *swap_map; /* vmalloc'ed array of usage counts */ > @@ -274,6 +273,16 @@ struct swap_info_struct { > */ > struct work_struct discard_work; /* discard worker */ > struct swap_cluster_list discard_clusters; /* discard clusters list */ > + struct plist_node avail_lists[0]; /* > + * entries in swap_avail_heads, one > + * entry per node. > + * Must be last as the number of the > + * array is nr_node_ids, which is not > + * a fixed value so have to allocate > + * dynamically. > + * And it has to be an array so that > + * plist_for_each_* can work. > + */ > }; > > #ifdef CONFIG_64BIT > diff --git a/mm/swapfile.c b/mm/swapfile.c > index 8688ae65ef58..6e06821623f6 100644 > --- a/mm/swapfile.c > +++ b/mm/swapfile.c > @@ -2812,8 +2812,9 @@ static struct swap_info_struct *alloc_swap_info(void) > struct swap_info_struct *p; > unsigned int type; > int i; > + int size = sizeof(*p) + nr_node_ids * sizeof(struct plist_node); > > - p = kvzalloc(sizeof(*p), GFP_KERNEL); > + p = kvzalloc(size, GFP_KERNEL); > if (!p) > return ERR_PTR(-ENOMEM); > > -- > 2.17.2 > -- Michal Hocko SUSE Labs