From mboxrd@z Thu Jan 1 00:00:00 1970 Subject: Re: broken VM in 2.4.10-pre9 References: From: ebiederm@xmission.com (Eric W. Biederman) Date: 19 Sep 2001 15:37:26 -0600 In-Reply-To: Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: owner-linux-mm@kvack.org Return-Path: To: Alan Cox Cc: Daniel Phillips , Rob Fuller , linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: Alan Cox writes: > > On September 17, 2001 06:03 pm, Eric W. Biederman wrote: > > > 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. > > > > What do you suppose is the cost of the reverse map? I get the impression you > > > think it's more expensive than it is. > > We can keep the typical page table cost lower than now (including reverse > maps) just by doing some common sense small cleanups to get the page struct > down to 48 bytes on x86 While there is a size cost I suspect you will notice reverse maps a lot more in operations like fork where having them tripples the amount of memory that you need to copy. So you should see a double or more in the time it takes to do a fork. That I think is a significant cost. 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/