From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id 1914C6B1EB1 for ; Tue, 21 Aug 2018 08:30:27 -0400 (EDT) Received: by mail-wm0-f69.google.com with SMTP id c14-v6so2180215wmb.2 for ; Tue, 21 Aug 2018 05:30:27 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id p65-v6sor4202147wrc.66.2018.08.21.05.30.25 for (Google Transport Security); Tue, 21 Aug 2018 05:30:25 -0700 (PDT) Date: Tue, 21 Aug 2018 14:30:24 +0200 From: Oscar Salvador Subject: Re: [PATCH] mm: Fix comment for NODEMASK_ALLOC Message-ID: <20180821123024.GA9489@techadventures.net> References: <20180820085516.9687-1-osalvador@techadventures.net> <20180820142440.1f9ccbebefc5d617c881b41e@linux-foundation.org> <20180821121734.GA29735@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180821121734.GA29735@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrew Morton , tglx@linutronix.de, joe@perches.com, arnd@arndb.de, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Oscar Salvador On Tue, Aug 21, 2018 at 02:17:34PM +0200, Michal Hocko wrote: > 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. No, maximum we can get is 1024 NUMA nodes. I checked this when writing another patch [1], and since having gone through all archs Kconfigs, CONFIG_NODES_SHIFT=10 is the limit. NODEMASK_ALLOC gets only called from: - unregister_mem_sect_under_nodes() (not anymore after [1]) - __nr_hugepages_store_common (This does not seem to have a deep stack, we could use a normal nodemask_t) But is also used for NODEMASK_SCRATCH (mainly used for mempolicy): struct nodemask_scratch { nodemask_t mask1; nodemask_t mask2; }; that would make 256 bytes in case CONFIG_NODES_SHIFT=10. I am not familiar with mempolicy code, I am not sure if we can do without that and figure out another way to achieve the same. [1] https://patchwork.kernel.org/patch/10566673/#22179663 -- Oscar Salvador SUSE L3