From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: broken VM in 2.4.10-pre9 References: <878A2048A35CD141AD5FC92C6B776E4907BB98@xchgind02.nsisw.com> From: ebiederm@xmission.com (Eric W. Biederman) Date: 17 Sep 2001 10:03:06 -0600 In-Reply-To: <878A2048A35CD141AD5FC92C6B776E4907BB98@xchgind02.nsisw.com> Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org Return-Path: To: Rob Fuller Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: "Rob Fuller" writes: > One argument for reverse mappings is distributed shared memory or > distributed file systems and their interaction with memory mapped > files. For example, a distributed file system may need to invalidate a specific > page of a file that may be mapped multiple times on a node. To reduce the time for an invalidate is indeed a good argument for reverse maps. However this is generally the uncommon case, and it is fine to leave this kinds of things on the slow path. From struct page we currently go to struct address_space to lists of struct vm_area which works but is just a little slower (but generally cheaper) than having a reverse map. Since Rik was not seeing the invalidate or the unmap case as the bottleneck this reverse mappings are not needed simply something with a similiar effect on the VM. In linux we have avoided reverse maps (unlike the BSD's) which tends to make the common case fast at the expense of making it more difficult to handle times when the VM system is under extreme load and we are swapping etc. Eric -- 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/