From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 4628B90023D for ; Fri, 24 Jun 2011 22:43:06 -0400 (EDT) Received: by pvc12 with SMTP id 12so2606515pvc.14 for ; Fri, 24 Jun 2011 19:43:03 -0700 (PDT) Message-ID: <4E054B0D.9090802@vflare.org> Date: Fri, 24 Jun 2011 19:42:21 -0700 From: Nitin Gupta MIME-Version: 1.0 Subject: Re: frontswap/zcache: xvmalloc discussion References: <4E023F61.8080904@linux.vnet.ibm.com> <4E042A84.5010204@vflare.org> <1308930764.11430.462.camel@nimitz> In-Reply-To: <1308930764.11430.462.camel@nimitz> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: Seth Jennings , linux-mm , Dan Magenheimer , Robert Jennings , Brian King , Greg Kroah-Hartman On 06/24/2011 08:52 AM, Dave Hansen wrote: > On Thu, 2011-06-23 at 23:11 -0700, Nitin Gupta wrote: >> Much of this vpage functionality seems to be already present in mainline >> as "flexible arrays"[1] > > That's a good observation. I don't know who wrote that junk, but I bet > they never thought of using it for this purpose. :) > > FWIW, for flex_arrays, the biggest limitation is that the objects > currently can not cross page boundaries. The current API also doesn't > have any concept of a release function. We'd need those to do the > unmapping after a get(). It certainly wouldn't be impossible to fix, > but it would probably make it quite a bit more complicated. > > The other limitation is that each array can only hold a small number of > megabytes worth of data in each array. We only have a single-level > table lookup, and that first-level table is limited to PAGE_SIZE (minus > a wee bit of metadata). > These limitations really makes them unsuitable for use in the new allocator and I guess "fixing" them is also not a good idea -- if its fundamentally designed to work on small number of objects, it should probably be left as-is. Not sure who really uses flex arrays? So, if and when vpage stuff is introduced, existence of flex_arrays should not become a barrier. Thanks, Nitin -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org