From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-f71.google.com (mail-it0-f71.google.com [209.85.214.71]) by kanga.kvack.org (Postfix) with ESMTP id 9120E83093 for ; Thu, 25 Aug 2016 15:55:45 -0400 (EDT) Received: by mail-it0-f71.google.com with SMTP id e63so5356328ith.2 for ; Thu, 25 Aug 2016 12:55:45 -0700 (PDT) Received: from resqmta-ch2-08v.sys.comcast.net (resqmta-ch2-08v.sys.comcast.net. [2001:558:fe21:29:69:252:207:40]) by mx.google.com with ESMTPS id e123si20000088iof.90.2016.08.25.12.55.44 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 25 Aug 2016 12:55:44 -0700 (PDT) Date: Thu, 25 Aug 2016 14:55:43 -0500 (CDT) From: Christoph Lameter Subject: Re: what is the purpose of SLAB and SLUB (was: Re: [PATCH v3] mm/slab: Improve performance of gathering slabinfo) stats In-Reply-To: <20160825100707.GU2693@suse.de> Message-ID: 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> Content-Type: text/plain; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman 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 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. > 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? 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. > Batching of tree_lock during reclaim for large files and swapping is also > relatively low hanging fruit that also is doable in a week or two. Ok these are good incremental improvement but they do not address the main issue going forward. > A high-order per-cpu cache for SLUB to reduce zone->lock contention is > also relatively low hanging fruit with the caveat it makes per_cpu_pages > larger than a cache line. Would be great to have. > If you want to rework the VM to use a larger fundamental unit, track > sub-units where required and deal with the internal fragmentation issues > then by all means go ahead and deal with it. Hmmm... The time problem is always there. Tried various approaches over the last decade. Could be a massive project. We really would need a larger group of developers to effectively do this. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org