From mboxrd@z Thu Jan 1 00:00:00 1970 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965403AbeALXhh (ORCPT + 1 other); Fri, 12 Jan 2018 18:37:37 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:58574 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965260AbeALXhg (ORCPT ); Fri, 12 Jan 2018 18:37:36 -0500 Date: Fri, 12 Jan 2018 15:37:34 -0800 From: Andrew Morton To: Pavel Tatashin Cc: steven.sistare@oracle.com, daniel.m.jordan@oracle.com, mgorman@techsingularity.net, mgorman@suse.de, mhocko@suse.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v1] mm: initialize pages on demand during boot Message-Id: <20180112153734.1780ccc00ebced508fad397a@linux-foundation.org> In-Reply-To: <20180112183405.22193-1-pasha.tatashin@oracle.com> References: <20180112183405.22193-1-pasha.tatashin@oracle.com> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Return-Path: On Fri, 12 Jan 2018 13:34:05 -0500 Pavel Tatashin wrote: > Deferred page initialization allows the boot cpu to initialize a small > subset of the system's pages early in boot, with other cpus doing the rest > later on. > > It is, however, problematic to know how many pages the kernel needs during > boot. Different modules and kernel parameters may change the requirement, > so the boot cpu either initializes too many pages or runs out of memory. > > To fix that, initialize early pages on demand. This ensures the kernel > does the minimum amount of work to initialize pages during boot and leaves > the rest to be divided in the multithreaded initialization path > (deferred_init_memmap). > > The on-demand code is permanently disabled using static branching once > deferred pages are initialized. After the static branch is changed to > false, the overhead is up-to two branch-always instructions if the zone > watermark check fails or if rmqueue fails. Presumably this fixes some real-world problem which someone has observed? Please describe that problem for us in lavish detail.