From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail202.messagelabs.com (mail202.messagelabs.com [216.82.254.227]) by kanga.kvack.org (Postfix) with SMTP id 534556B006A for ; Thu, 14 Jan 2010 02:30:59 -0500 (EST) Received: from m3.gw.fujitsu.co.jp ([10.0.50.73]) by fgwmail5.fujitsu.co.jp (Fujitsu Gateway) with ESMTP id o0E7UqNi015897 for (envelope-from kosaki.motohiro@jp.fujitsu.com); Thu, 14 Jan 2010 16:30:53 +0900 Received: from smail (m3 [127.0.0.1]) by outgoing.m3.gw.fujitsu.co.jp (Postfix) with ESMTP id 7510545DE50 for ; Thu, 14 Jan 2010 16:30:52 +0900 (JST) Received: from s3.gw.fujitsu.co.jp (s3.gw.fujitsu.co.jp [10.0.50.93]) by m3.gw.fujitsu.co.jp (Postfix) with ESMTP id 3F29D45DE4E for ; Thu, 14 Jan 2010 16:30:52 +0900 (JST) Received: from s3.gw.fujitsu.co.jp (localhost.localdomain [127.0.0.1]) by s3.gw.fujitsu.co.jp (Postfix) with ESMTP id 242F4E08002 for ; Thu, 14 Jan 2010 16:30:52 +0900 (JST) Received: from ml14.s.css.fujitsu.com (ml14.s.css.fujitsu.com [10.249.87.104]) by s3.gw.fujitsu.co.jp (Postfix) with ESMTP id C177B1DB803B for ; Thu, 14 Jan 2010 16:30:51 +0900 (JST) From: KOSAKI Motohiro Subject: Re: [PATCH v5] add MAP_UNLOCKED mmap flag In-Reply-To: <20100114072210.GK18808@redhat.com> References: <20100114155229.6735.A69D9226@jp.fujitsu.com> <20100114072210.GK18808@redhat.com> Message-Id: <20100114162327.673E.A69D9226@jp.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Date: Thu, 14 Jan 2010 16:30:51 +0900 (JST) Sender: owner-linux-mm@kvack.org To: Gleb Natapov Cc: kosaki.motohiro@jp.fujitsu.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, akpm@linux-foundation.org List-ID: > On Thu, Jan 14, 2010 at 04:02:42PM +0900, KOSAKI Motohiro wrote: > > > On Thu, Jan 14, 2010 at 09:31:03AM +0900, KOSAKI Motohiro wrote: > > > > > If application does mlockall(MCL_FUTURE) it is no longer possible to mmap > > > > > file bigger than main memory or allocate big area of anonymous memory > > > > > in a thread safe manner. Sometimes it is desirable to lock everything > > > > > related to program execution into memory, but still be able to mmap > > > > > big file or allocate huge amount of memory and allow OS to swap them on > > > > > demand. MAP_UNLOCKED allows to do that. > > > > > > > > > > Signed-off-by: Gleb Natapov > > > > > --- > > > > > > > > > > I get reports that people find this useful, so resending. > > > > > > > > This description is still wrong. It doesn't describe why this patch is useful. > > > > > > > I think the text above describes the feature it adds and its use > > > case quite well. Can you elaborate what is missing in your opinion, > > > or suggest alternative text please? > > > > My point is, introducing mmap new flags need strong and clearly use-case. > > All patch should have good benefit/cost balance. the code can describe the cost, > > but the benefit can be only explained by the patch description. > > > > I don't think this poor description explained bit benefit rather than cost. > > you should explain why this patch is useful and not just pretty toy. > > > The benefit is that with this patch I can lock all of my application in > memory except some very big memory areas. My use case is that I want to > run virtual machine in such a way that everything related to machine > emulator is locked into the memory, but guest address space can be > swapped out at will. Guest address space is so huge that it is not > possible to allocated it locked and then unlock. I was very surprised > that current Linux API has no way to do it hence this patch. It may look > like a pretty toy to you until some day you need this and has no way to > do it. Hmm.. Your answer didn't match I wanted. few additional questions. - Why don't you change your application? It seems natural way than kernel change. - Why do you want your virtual machine have mlockall? AFAIK, current majority virtual machine doesn't. - If this feature added, average distro user can get any benefit? I mean, many application developrs want to add their specific feature into kernel. but if we allow it unlimitedly, major syscall become the trushbox of pretty toy feature soon. -- 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