From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id 2332A6B004D for ; Sat, 27 Jun 2009 07:27:58 -0400 (EDT) Date: Wed, 24 Jun 2009 17:04:21 +0200 From: Pavel Machek Subject: Re: [RFC] transcendent memory for Linux Message-ID: <20090624150420.GH1784@ucw.cz> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org To: Dan Magenheimer Cc: linux-kernel@vger.kernel.org, xen-devel@lists.xensource.com, npiggin@suse.de, chris.mason@oracle.com, kurt.hackel@oracle.com, dave.mccracken@oracle.com, Avi Kivity , jeremy@goop.org, Rik van Riel , alan@lxorguk.ukuu.org.uk, Rusty Russell , Martin Schwidefsky , akpm@osdl.org, Marcelo Tosatti , Balbir Singh , tmem-devel@oss.oracle.com, sunil.mushran@oracle.com, linux-mm@kvack.org, Himanshu Raj List-ID: Hi! This description (whole mail) needs to go into Documentation/, somewhere. > Normal memory is directly addressable by the kernel, > of a known normally-fixed size, synchronously accessible, > and persistent (though not across a reboot). ... > Transcendent memory, or "tmem" for short, provides a > well-defined API to access this unusual class of memory. > The basic operations are page-copy-based and use a flexible > object-oriented addressing mechanism. Tmem assumes Should this API be documented, somewhere? Is it in-kernel API or does userland see it? > "Preswap" IS persistent, but for various reasons may not always > be available for use, again due to factors that may not be > visible to the kernel (but, briefly, if the kernel is being > "good" and has shared its resources nicely, then it will be > able to use preswap, else it will not). Once a page is put, > a get on the page will always succeed. So when the kernel > finds itself in a situation where it needs to swap out a page, > it first attempts to use preswap. If the put works, a disk > write and (usually) a disk read are avoided. If it doesn't, > the page is written to swap as usual. Unlike precache, whether Ok, how much slower this gets in the worst case? Single hypercall to find out that preswap is unavailable? I guess that compared to disk access that's lost in the noise? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html -- 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