From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-f199.google.com (mail-pf1-f199.google.com [209.85.210.199]) by kanga.kvack.org (Postfix) with ESMTP id B172F6B1EA0 for ; Tue, 21 Aug 2018 08:17:40 -0400 (EDT) Received: by mail-pf1-f199.google.com with SMTP id i68-v6so9648249pfb.9 for ; Tue, 21 Aug 2018 05:17:40 -0700 (PDT) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id e3-v6si12509684pgh.385.2018.08.21.05.17.39 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 21 Aug 2018 05:17:39 -0700 (PDT) Date: Tue, 21 Aug 2018 14:17:34 +0200 From: Michal Hocko Subject: Re: [PATCH] mm: Fix comment for NODEMASK_ALLOC Message-ID: <20180821121734.GA29735@dhcp22.suse.cz> References: <20180820085516.9687-1-osalvador@techadventures.net> <20180820142440.1f9ccbebefc5d617c881b41e@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180820142440.1f9ccbebefc5d617c881b41e@linux-foundation.org> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: Oscar Salvador , tglx@linutronix.de, joe@perches.com, arnd@arndb.de, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Oscar Salvador On Mon 20-08-18 14:24:40, Andrew Morton wrote: > On Mon, 20 Aug 2018 10:55:16 +0200 Oscar Salvador wrote: > > > From: Oscar Salvador > > > > Currently, NODEMASK_ALLOC allocates a nodemask_t with kmalloc when > > NODES_SHIFT is higher than 8, otherwise it declares it within the stack. > > > > The comment says that the reasoning behind this, is that nodemask_t will be > > 256 bytes when NODES_SHIFT is higher than 8, but this is not true. > > For example, NODES_SHIFT = 9 will give us a 64 bytes nodemask_t. > > Let us fix up the comment for that. > > > > Another thing is that it might make sense to let values lower than 128bytes > > be allocated in the stack. > > Although this all depends on the depth of the stack > > (and this changes from function to function), I think that 64 bytes > > is something we can easily afford. > > So we could even bump the limit by 1 (from > 8 to > 9). > > > > I agree. Such a change will reduce the amount of testing which the > kmalloc version receives, but I assume there are enough people out > there testing with large NODES_SHIFT values. We do have CONFIG_NODES_SHIFT=10 in our SLES kernels for quite some time (around SLE11-SP3 AFAICS). Anyway, isn't NODES_ALLOC over engineered a bit? Does actually even do larger than 1024 NUMA nodes? This would be 128B and from a quick glance it seems that none of those functions are called in deep stacks. I haven't gone through all of them but a patch which checks them all and removes NODES_ALLOC would be quite nice IMHO. -- Michal Hocko SUSE Labs