From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757942AbcH3JkP (ORCPT ); Tue, 30 Aug 2016 05:40:15 -0400 Received: from mx2.suse.de ([195.135.220.15]:52653 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757912AbcH3JkK (ORCPT ); Tue, 30 Aug 2016 05:40:10 -0400 Date: Tue, 30 Aug 2016 10:39:55 +0100 From: Mel Gorman To: Christoph Lameter Cc: Michal Hocko , Joonsoo Kim , Aruna Ramakrishna , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mike Kravetz , Pekka Enberg , David Rientjes , Andrew Morton , Jiri Slaby Subject: Re: what is the purpose of SLAB and SLUB (was: Re: [PATCH v3] mm/slab: Improve performance of gathering slabinfo) stats Message-ID: <20160830093955.GV2693@suse.de> References: <1471458050-29622-1-git-send-email-aruna.ramakrishna@oracle.com> <20160818115218.GJ30162@dhcp22.suse.cz> <20160823021303.GB17039@js1304-P5Q-DELUXE> <20160823153807.GN23577@dhcp22.suse.cz> <20160824082057.GT2693@suse.de> <20160825100707.GU2693@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 25, 2016 at 02:55:43PM -0500, Christoph Lameter wrote: > On Thu, 25 Aug 2016, Mel Gorman wrote: > > > Flipping the lid aside, there will always be a need for fast management > > of 4K pages. The primary use case is networking that sometimes uses > > high-order pages to avoid allocator overhead and amortise DMA setup. > > Userspace-mapped pages will always be 4K although fault-around may benefit > > from bulk allocating the pages. That is relatively low hanging fruit that > > would take a few weeks given a free schedule. > > Userspace mapped pages can be hugepages as well as giant pages and that > has been there for a long time. Intermediate sizes would be useful too in > order to avoid having to keep lists of 4k pages around and continually > scan them. > Userspace pages cannot always be mapped as huge or giant. mprotect on a 4K boundary is an obvious example. > > Dirty tracking of pages on a 4K boundary will always be required to avoid IO > > multiplier effects that cannot be side-stepped by increasing the fundamental > > unit of allocation. > > Huge pages cannot be dirtied? I didn't say that, I said they are required to avoid IO multiplier effects. If a file is mapped as 2M or 1G then even a 1 byte write requires 2M or 1G of IO to writeback. > This is an issue of hardware support. On > x867 you only have one size. I am pretty such that even intel would > support other sizes if needed. The case has been repeatedly made that 64k > pages f.e. would be useful to have on x86. > 64K pages are not a universal win even on the arches that do support them. -- Mel Gorman SUSE Labs