From mboxrd@z Thu Jan 1 00:00:00 1970 Received: by zproxy.gmail.com with SMTP id k1so316775nzf for ; Thu, 20 Oct 2005 18:57:02 -0700 (PDT) Message-ID: Date: Fri, 21 Oct 2005 10:57:02 +0900 From: Magnus Damm Subject: Re: [PATCH 0/4] Swap migration V3: Overview In-Reply-To: <20051020225935.19761.57434.sendpatchset@schroedinger.engr.sgi.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Content-Disposition: inline References: <20051020225935.19761.57434.sendpatchset@schroedinger.engr.sgi.com> Sender: owner-linux-mm@kvack.org Return-Path: To: Christoph Lameter Cc: akpm@osdl.org, Mike Kravetz , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Marcelo Tosatti List-ID: On 10/21/05, Christoph Lameter wrote: > Page migration is also useful for other purposes: > > 1. Memory hotplug. Migrating processes off a memory node that is going > to be disconnected. > > 2. Remapping of bad pages. These could be detected through soft ECC errors > and other mechanisms. 3. Migrating between zones. The current per-zone LRU design might have some drawbacks. I would prefer a per-node LRU to avoid that certain zones needs to shrink more often than others. But maybe that is not the case, please let me know if I'm wrong. If you think about it, say that a certain user space page happens to be allocated from the DMA zone, and for some reason this DMA zone is very popular because you have crappy hardware, then it might be more probable that this page is paged out before some other much older/less used page in another (larger) zone. And I guess the same applies to small HIGHMEM zones. This could very well be related to the "1 GB Memory is bad for you" problem described briefly here: http://kerneltrap.org/node/2450 Maybe it is possible to have a per-node LRU and always page out the least recently used page in the entire node, and then migrate pages to solve specific "within N bits of address space" requirements. But I'm probably underestimating the cost of page migration... / magnus -- 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