From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx146.postini.com [74.125.245.146]) by kanga.kvack.org (Postfix) with SMTP id 59F486B0032 for ; Thu, 9 May 2013 11:41:51 -0400 (EDT) Message-ID: <518BC3BD.30005@sr71.net> Date: Thu, 09 May 2013 08:41:49 -0700 From: Dave Hansen MIME-Version: 1.0 Subject: Re: [RFC PATCH 00/22] Per-cpu page allocator replacement prototype References: <1368028987-8369-1-git-send-email-mgorman@suse.de> In-Reply-To: <1368028987-8369-1-git-send-email-mgorman@suse.de> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Mel Gorman Cc: Linux-MM , Johannes Weiner , Christoph Lameter , LKML On 05/08/2013 09:02 AM, Mel Gorman wrote: > So preliminary testing indicates the results are mixed bag. As long as > locks are not contended, it performs fine but parallel fault testing > hits into spinlock contention on the magazine locks. A greater problem > is that because CPUs share magazines it means that the struct pages are > frequently dirtied cache lines. If CPU A frees a page to a magazine and > CPU B immediately allocates it then the cache line for the page and the > magazine bounces and this costs. It's on the TODO list to research if the > available literature has anything useful to say that does not depend on > per-cpu lists and the associated problems with them. If we don't want to bounce 'struct page' cache lines around, then we _need_ to make sure that things that don't share caches don't use the same magazine. I'm not sure there's any other way. But, that doesn't mean we have to _statically_ assign cores/thread to particular magazines. Say we had a percpu hint which points us to the last magazine we used. We always go to it first, and fall back to round-robin if our preferred one is contended. That way, if we have a mixture tasks doing heavy and light allocations, the heavy allocators will tend to "own" a magazine, and the lighter ones would gravitate to sharing one. It might be taking things too far, but we could even raise the number of magazines only when we actually *see* contention on the existing set. > 24 files changed, 571 insertions(+), 788 deletions(-) oooooooooooooooooohhhhhhhhhhhhh. The only question is how much we'll have to bloat it as we try to optimize things. :) BTW, I really like the 'magazine' name. It's not frequently used in this kind of context and it conjures up a nice mental image whether it be of stacks of periodicals or firearm ammunition clips. -- 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