Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756388Ab0BLNxr (ORCPT ); Fri, 12 Feb 2010 08:53:47 -0500 Received: from fxip-0047f.externet.hu ([88.209.222.127]:43654 "EHLO pomaz-ex.szeredi.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755758Ab0BLNxk (ORCPT ); Fri, 12 Feb 2010 08:53:40 -0500 To: Tejun Heo CC: miklos@szeredi.hu, mszeredi@suse.cz, linux-kernel@vger.kernel.org, fuse-devel@lists.sourceforge.net, polynomial-c@gentoo.org, akpm@linux-foundation.org In-reply-to: <4B7558C1.2060405@kernel.org> (message from Tejun Heo on Fri, 12 Feb 2010 22:33:53 +0900) Subject: Re: [fuse-devel] [PATCH] FUSE/CUSE: implement direct mmap support References: <4B70FBE4.7050700@kernel.org> <4B7296DF.207@kernel.org> <4B729F07.8020704@kernel.org> <4B72A802.6040009@kernel.org> <4B7344A4.1030607@kernel.org> <4B73EE68.4070004@kernel.org> <4B73FE96.2080707@kernel.org> <4B74065D.2000707@kernel.org> <4B740CFB.7060409@kernel.org> <4B749BDF.8000807@kernel.org> <4B7558C1.2060405@kernel.org> Message-Id: From: Miklos Szeredi Date: Fri, 12 Feb 2010 14:53:27 +0100 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2089 Lines: 46 On Fri, 12 Feb 2010, Tejun Heo wrote: > > 3) on the low level API don't make it an offset pointer that is > > adjusted. It's not an offset to be either left alone or changed > > (that would be the case if we wanted to allow adjustment to > > vma->vm_pgoff itself). It's about calclulating a completely new > > offset for the server side mmap. > > And now I'm completely lost. So, we'll assign new offset (no matter > how it is called) but it doesn't have to be aligned? It seems like > we've been having this disconnection from the beginning. Can you > please describe how this can avoid aliasing issues between clients > sharing the same page? So, in 2), whatever it is called, the server > specifies a value, how is that value used? That dev_offset value is used as an offset into the server side mmap address space. And yes, vma->vm_pgoff and dev_offset should be SHMLBA multiples apart. But don't call that _adjustment_. That's totally confusing, these are *two* *different* *offsets*. There's an alignment requirement but that's all. If they are the same that is pure coincidence. And dev_offset (which points into the dmmap address space) is only required if the filesystem/CUSE driver needs server side mmap. > > In fact most of what is required is already there in the form of the > > page cache. What I think would be interesting to be able to > > load/save contents of page cache from the server side, and not > > necessarily using server side mmaps (server side mmap is also a > > possibility, but not an easy one if it has to cooperate with the > > page cache). > > Device mmap use cases might not work very well if the server can't > mmap directly. I understand that, and that's where the interesting part comes in: make the mmap API in a way that it works with and without server side mmap. Thanks, Miklos -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/